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6.7.1 Defining turbulence and wind shear Turbulence It is usual to classify all the changes in atmospheric motion that significantly disturb aircraft flight as turbulence, but in some wind shear events there may be no air turbulence involved. It is difficult to define the degree of turbulence or the load effects of shear in a way that is meaningful to a recreational and sport aviation pilot. Measuring by the airflow velocity change or the gust velocity measured in feet per second doesn't really enable the pilot to judge how turbulent the conditions are in their circumstances, particularly so if the instrument panel is not equipped with an accelerometer or variometer. The following is based on an old ICAO turbulence scale which, though classifying by the induced positive or negative accelerations (only as measured near the aircraft cg), does provide a descriptive definition of sorts that is appropriate for three-axis aircraft, but perhaps not so meaningful for flexible-wing weight-shift aircraft (powered or unpowered) and certainly not meaningful for powered-parachutes or paragliders. Very low — below 0.05g; light pitch, yaw and roll oscillations are experienced. Low — 0.05 to 0.2g; aircraft might experience light to moderate 'chop', i.e. slight, rapid, rhythmic bumps and oscillations but any without significant changes in altitude or attitude. Like driving a boat through a choppy sea. Also known as 'cobblestoning' — like driving at moderate speed on a corrugated gravel road. Moderate — 0.2 to 0.5g; turbulence is becoming significant and the ride produces strong, intermittent, uncomfortable jolts with attitude upsets and indicated airspeed variations, but the aircraft remains in control. The occupants' heads may hit the cockpit roof structure if the clearance is small or the harness is not tight enough. Severe — 0.5 to 1.5g; the aircraft handling in all axes is made difficult but not dangerous except at lower alitudes — if occupants and objects properly secured.There are large, abrupt changes in altitude and attitude, and significant variations in indicated airspeed. Cockpit instruments are difficult to read. Very severe — above 1.5g; the aircraft is violently tossed about, with extreme handling difficulty. Aircraft may be out of control for short periods. Structural damage is possible. The wake vortices from aeroplanes and helicopters add another form of turbulence that is extremely hazardous to all recreational aircraft, particularly because of the strong rotational effects that lead to sudden height loss. Such vortices must be anticipated and avoided. Wind shear In aviation terms, wind shear is a sudden but sustained "variation in wind along the flight path of a pattern, intensity and duration, that displaces the aircraft abruptly from its intended path and sufficiently that substantial and timely control action is needed". Wind shear is probably the greatest hazard to flight at low levels in visual meteorological conditions, but its effect is short-lived. Displacement in the flight path is initiated by a substantial change in lift generation associated with the aircraft's inertia (see Note 1 following). The shearing action between air layers with substantially differing velocities — or vertical gusts and their surrounds — may also induce strong turbulent eddies or breaking waves at the shearing level or interface. Note: inertia is the property of resisting any change in motion, or continuing in the same state of rest or state of motion relative to the Earth's cg. The mass of a body is a measure of its inertia; i.e. its resistance to being accelerated or decelerated by an applied force (such as a change in aerodynamic lift) increases with mass. An aircraft in flight is 'airborne' and its true airspeed is relative to the surrounding air, not the Earth's surface. However, when the aircraft encounters a sudden change in the ambient air energy/velocity — even just a transient gust, horizontal or vertical — inertia comes into play and momentarily maintains the aircraft motion relative to the Earth or — more correctly — relative to space. This changes aoa and airspeed, and imparts other forces (e.g. drag and pitching moments) to the aircraft. A heavier aircraft has more inertia than a lighter one, so is more resistant to irregular, random displacement forces — atmospheric turbulence. The fact that inertia momentarily overrides the physics of aerodynamics is sometimes a cause of confusion. As long as an aircraft's mass remains unchanged so will its inertia whether it is at rest or moving; i.e. motion or pulling g has absolutely no effect on an aircraft's inertia but speed does affect momentum, which is mass (or inertia) × velocity. Wind shear can be induced by the terrain, constructed obstructions, passage of cold fronts, convective downbursts, thermals, temperature inversions, low-level jets and other sources; all of which will be described later. The closer to the surface that the shear occurs the more hazardous for aircraft — and particularly so for very light aircraft. For an aircraft taking off, landing or going around, the shear may be large enough and rapid enough to exceed the airspeed safety margin and the aircraft's capability to accelerate or climb; or the pilot just may not be able to recover an uncommanded roll due to a crosswind gust, before a ground strike occurs. The shear is the rate of change of wind speed and/or direction experienced by the aircraft, Such events tend to be classified as 'vertical' or 'horizontal' shear, though many, perhaps most, shear encounters are a combination of both. There is a third classification — 'vertical gust' shear — which has the greatest potential to produce extreme structural loads and which we will examine first. 6.7.2 Vertical gust shear Gust categorisation Vertical gust shear, chiefly associated with updrafts and downdrafts, is the change in the predominantly vertical air motion with horizontal distance flown. Thermals can produce very severe updraft shear when flying in the unstable, high-temperature superadiabatic boundary layer conditions endemic to inland Australia, though their vertical speed near the surface may be relatively low but accelerating with height. There is a noticeable transition gradient between the surrounding air and a well-ordered updraft/downdraft core; also the ascending/descending column tends to entrain some surrounding air, creating a turbulent interface around it. It is possible that a cruising aircraft suddenly encounters an area of substantial vertical motion. The sudden entry (an aircraft cruising at just 60 knots is moving at 100 feet per second) into such a strong vertical gust is a hazardous form of shear. Apart from fast-rising thermals, such events are also associated with downdrafts from large, vertically developed convective clouds. Note: the categorisation of vertical gusts is not the same as the usual atmospheric turbulence. The meteorological categories for wind gusts in general (as measured with an anemometer) are: Category 1: weak — ≥ 5 m/s to <10 m/s Category 2: moderate — ≥ 10 m/s to <15 m/s Category 3: strong — ≥ 15 m/s to <25 m/s Category 4: severe — ≥ 25 m/s The meteorological categorisation restated for vertical gust measurement might be: Weak — ≥ 16 fps to <25 fps Moderate to strong — ≥ 25 fps to <50 fps Strong to severe — ≥ 50 fps to <80 fps Extreme — ≥ 80 fps (or 66 fps [20 m/s] might be used) Speed conversion table (values rounded) Metres per second Feet per second Feet per minute Knots 5 m/s 16 fps 1000 fpm 10 7.5 m/s 25 fps 1500 fpm 15 10 m/s 33 fps 2000 fpm 20 15 m/s 50 fps 3000 fpm 30 20 m/s 66 fps 4000 fpm 40 25 m/s 80 fps 5000 fpm 50 It is probable that 60% of vertical gusts associated with thunderstorms have velocities of 10 fps or less, while 35% are in the 10 to 25 fps range. An encounter with a gust over 50 fps would be rare — but of course it does happen and always when you don't expect it; see this recreational pilot's report. Vertical gust shear effects On entering a gust, inertia will momentarily maintain the aircraft's flight path relative to the Earth's cg. For a very short period the 'effective airstream' around the wings will no longer be aligned with the flight path but will have acquired a vertical component. So, the aircraft's effective angle of attack [aoa] must alter — with a consequent change in the lift and drag coefficients, plus a change in wing loading. The combination of updraft/downdraft velocity with the aircraft's forward speed also produces a change in the effective airspeed relative to the wing, which also affects the wing loading. But in purely vertical gust encounters, this is very slight in comparison to the aoa change and can be ignored. The reverse happens in encounters with purely horizontal gusts — the aoa change is slight in comparison to effective airspeed change. Most turbulence or shear encounters incorporate vertical, horizontal and lateral components, and will affect aoa, airspeed and attitude. Table 7.1 shows the approximate addition to, or subtraction from, the original aoa experienced by four imaginary aircraft each in level flight at a cruise speed where the aoa is 4° and encountering vertical updrafts or downdrafts of the speed shown. Such angles are readily calculated using the 1-in-60 rule; i.e. angular change = gust speed/aircraft speed × 60. The values in red indicate where the stalling aoa, presumed to be 16°, would be exceeded and thus any gust-induced loading is alleviated (with a momentary delay due the aircraft inertia), but the stall indication is applicable only to updrafts and not downdrafts. I have used these reasonably close approximations: (a) to convert knots to metres per second, divide by 2; (b) to convert knots to feet per minute, multiply by 100; (c) to convert feet per minute to metres per second, divide by 200. Table 7.1: increment or decrement in aoa due to vertical gusts encountered at the cruising airspeeds shown and aoa 4° Vertical component of air current 60 knots (6000 fpm) 75 knots (7500 fpm) 100 knots (10 000 fpm) 120 knots (12 000 fpm) 500 fpm (8 fps) 5° 4° 3° 2.5° 1000 fpm (17 fps) 10° 8° 6° 5° 1500 fpm (25 fps) 15° 12° 9° 7.5° 1750 fpm (29 fps) 17.5° 14° 10.5° 9° 2000 fpm (33 fps) 20° 16° 12° 10° Encounter with an updraft For example let's look at a two-seat aeroplane (we'll call it 'Model A') with a wing area of 10 m², cruising at 50 m/s (100 knots TAS) at its MTOW of 540 kg and at an altitude where the air density is 1 kg/m³ — about 6000 feet. The lift force being produced must equal the gross aircraft weight (mass multiplied by the acceleration of gravity, which is near enough to 10 m/s²), thus the weight is 540 × 10 = 5400 newtons [N] and the lift from the wing must be the same — ignoring the tailplane/canard balance needs. The lift equation in level flight is: lift = CL × ½rV² × S = weight where CL is the non-dimensional lift coefficient, r is the air density in kg/m³, V is the true airspeed in m/s and S is the wing area in m². Substituting the Model A values in the equation, then CL × ½ × 1 × 50 × 50 × 10 = 5400 so the value of CL in the cruise with zero flap must be 0.43 and aoa would be around 4°. The 'lift coefficient — aoa curve' diagram is a generalisation of the relationship between CL and aoa for a normally cambered wing, which reaches the zero lift aoa at around 2° negative, and the critical aoa at 16° where CLmax is 1.3. The slope of the 'lift curve' is such that each 1° aoa change, within the 2° to 12° range, increases/decreases CL by around 0.1. Now suppose our Model A aeroplane cruising at 50 m/s encounters a sharp-edged thermal that has a velocity of 7.5 m/s (1500 fpm or 25 fps), then the aircraft aoa will increase by 9° to about 13°. (Using the 1-in-60 rule: 7.5/50 × 60 = 9.) In addition, the speed of the airflow relative to the wing will increase very slightly to 50.5 m/s as shown in the diagram 'Effect of updraft encounter on aoa' below. (The diagram is much the same as the wind triangle plot you might use in navigation — the 'effective change in aoa' is comparable to the drift angle, and the 'effective airspeed' is comparable to the ground speed.) The lift coefficient increases by around 0.1 per 1° aoa change so the value of CL will now be around 1.3, the 'CL — aoa curve' indicates 1.2. Ignoring the very slight airspeed change we can calculate the lift force produced under the changed conditions: i.e. lift force = 1.2 × ½ × 1 × 50 × 50 × 10 = 15 000 N. Thus entry to the gust has increased CL from 0.43 to 1.2 (i.e. 2.8 times) and induced a momentary increase in total wing loading from 5400 to 15 000 N. This applies a rapid bending moment to the wings, flexing them up but well within the design limit load for normal category aircraft of +3.8g, or 20 520 N (5400 × 3.8) total wing loading for our aircraft. (Design limit loads were discussed in the module 'Don't fly real fast', but be aware that the extension of flaps reduces the limit load factors by as much as 50%.) A very short time after that initial entry into the gust, the inertial effects are overcome, the +2.8g load (15 000/5400) accelerates the aircraft upwards — felt by the occupants as a very severe jolt pushing the seat up under them but also 'felt' as a sudden 2.8g load by all other parts of the aircraft's structure — and the wings' elastic reaction also adds some impetus to the fuselage. The acceleration alleviates the gust loads on the wing while the aircraft restores itself to its trimmed angle of attack and flight continues normally; except that the new flight path will incorporate a rate of ascent relative to the Earth, equivalent to the updraft speed. When the aircraft flies out of the updraft it will again momentarily maintain its flight path relative to the Earth. During that time the effective airflow around the wings will no longer be directly aligned with the flight path but will have acquired a vertical component opposite to that at entry. The aoa and consequently CL will decrease, producing a momentary decrease in wing loading. The airframe will experience a negative g load, and perhaps the occupants will feel the shoulder harness stopping them being thrown out of the seat, before the aircraft is finally restored to level, unaccelerated flight. Encounter with a strong updraft Now let's consider the Model A aircraft cruising at 120 knots (60 m/s) with CL of 0.3 encountering a 2000 fpm (10 m/s or 33 fps) gust. The encounter would increase aoa by 10° and CL to about 1.15, so: lift produced = 1.15 × ½ × 1 × 60 × 60 × 10 = 20 700 N. Thus entry to the gust has produced a momentary increase in total wing loading from 5400 to 20 700 N imparting a +3.8g load (20 700/5400), which is around the 20 520 N wing load limit as well as the 3.8g airframe load limit. The change in load is from +1g to +3.8g, which will impart a 2.8g acceleration. Note that if our aircraft had been cruising at less than 50 m/s, when the 10 m/s gust was encountered the aoa change would exceed 12° and consequently the critical aoa. The airflow over the wing would separate instantly and alleviate the gust load; this is relevant to Va, the design manoeuvre speed. It is also assumed above that the aircraft is in unaccelerated flight when the gust is encountered. If the aircraft were in a 40° banked turn then the manoeuvring load factor would be 1.3g rather than 1g, and the gust-induced load would be added to the basic manoeuvring load. If it were in a 60° banked turn then the basic load would be 2g, and the manoeuvre plus gust acceleration would be 4.8g; this is getting very close to the ultimate load factor and in the zone where component fatigue could cause premature structural failure. Effect of lower aircraft weight If an aircraft is well below MTOW there is a significant effect on structural loads developed in a vertical gust. Let's take our Model A with only one person on board and less fuel so that weight is reduced to 450 kg or 4500 N, again cruising at 60 m/s and still at an altitude where the air density is 1 kg/m³. So substituting those values in the equation then CL × ½ × 1 × 60 × 60 × 10 = 4500 and the value of CL in the cruise must now be reduced to 0.25 and the aoa reduced to about 1°. Now suppose that aircraft encounters the same 2000 fpm (10 m/s) updraft. Then the aircraft aoa will again increase by 10° but to about 11° and CL of 1.05. We can calculate the lift force produced under the changed conditions: lift produced = 1.05 × ½ × 1 × 60 × 60 × 10 = 18 900 N. Thus entry to the gust at the lower weight has increased CL from 0.25 to 1.05 (i.e. 4.2 times) and induced a momentary increase in total wing loading from 4500 to 18 900 N (4.2g). This is well within the 20 520 N (5400 × 3.8) total wing loading limit for this aircraft but outside the 3.8g design load limit for the structural parts — the mounting structures for the engine, battery and occupant seats, for example. So when operating at significantly lower weight (and thus lower wing loading) an encounter with a vertical gust at a particular flight speed will induce greater accelerations than when operating near MTOW, which obviously affects choice of speed in turbulent conditions. Effect of speed From the foregoing we could deduce that the faster a particular aircraft's speed is when encountering vertical gust shear, the lesser the structural loads developed. This is because the change in effective angle of attack will lessen as forward speed increases. However, angles of attack at higher speeds are much lower, so the effective CL change from a gust encounter is then proportionately greater. (But it depends to some extent on the slope of the lift curve and the wing loading.) For example, take our fully laden Model A flying at both 80 knots and 120 knots at 6000 feet; CL at the slower speed would be 0.7 and 0.3 at the faster speed. If, in both cases, the aircraft encountered a 500 fpm thermal the aoa changes would be about 4° and 2.5°, increasing CL to 1.0 and 0.5 respectively. The acceleration would be about 1.4g (1.0/0.7) at the slower speed but 1.7g (0.5/0.3) at the faster, so acceleration loads increase as airspeed increases and that increase is amplified by increasing gust velocity. This doesn't alter the fact that a high wing-loading aircraft will provide a better ride in turbulence than a low wing-loading [W/S] aircraft, at the same high speed. Imagine two different aircraft types having the same weight but different wing area; if they are flying at the same speed and encounter the same vertical gust, the change in aoa and thus CL will be roughly the same for both. However, the low W/S aircraft will experience a higher acceleration because its wing area is greater and thus the total induced load is greater. We will discuss speed to fly in turbulence later in this module. Encounter with a downdraft Now suppose the Model A aircraft cruising at 50 m/s (4° aoa) encounters a sharp-edged downdraft that has a velocity of 7.5 metres/second (1500 fpm). Then the aircraft aoa will decrease by 9° to about 5° negative where, from the CL – aoa curve, CL will perhaps be around 0.2 negative. The airspeed relative to the wing will change slightly but can be ignored. We can calculate the lift force produced under the changed conditions: lift force produced = –0.2 × ½ × 1 × 50 × 50 × 10 = −2500 N A negative value means the lift force is acting opposite to the norm. Thus the entry to the downdraft has produced a momentary change in total wing loading from 5400 N positive to 2500 N negative, producing a 0.5 negative g load (–2500/5400) and resulting in a 1.5g negative acceleration from +1g to –0.5g. The occupants will be restrained by their harnesses while the seat drops away from them. Following initial entry into the downdraft the inertial effects are overcome and the aircraft will restore itself to its trimmed angle of attack and flight will continue normally — except that the new flight path will incorporate a rate of sink relative to the Earth and equivalent to the atmospheric downflow. Note the difference in the acceleration between the 1500 fpm updraft and 1500 downdraft encounter at the same cruise speed — the updraft produced a 2.8g acceleration, the downdraft only a 1.5g acceleration. When the aircraft flies out of the downflow it will again momentarily maintain its flight path relative to the Earth. During that time the effective airflow around the wings will no longer be directly aligned with the flight path but will have acquired a vertical component opposite to that at entry. The aoa and consequently CL will increase producing a momentary increase in wing loading, and the airframe will experience a positive g load before the aircraft is finally re-established in level flight. Thus encountering changes in vertical flow induces momentary changes in aoa and wing loading. The gust accelerations and the variation in the vertical profile of the flight path will be considerable if extensive and higher-speed vertical gusts are encountered. But it's a bit more complex! The foregoing assessments of aircraft reaction to updraft/downdraft shear is simplified, but aircraft reactions are much more complex. For example: the calculations have been done assuming a 'sharp-edged gust' which probably doesn't exist; aircraft designers include a 'gust alleviation factor' in their calculations; the gust-induced aoa change also changes the wing pitching moments; the tailplane is flying perhaps 50 milliseconds behind the wing and will also be affected by the gust loads, so the stabiliser pitching moment will be out of sync with the wing pitching moment and the aircraft will pitch up or down accordingly; air velocity within the gust will not be smooth and constant, yawing and rolling forces will be applied, and buffeting may occur; changes in aoa must result in momentary changes in induced drag but the aircraft's inertia will probably maintain its motion; and a canard aircraft will be affected differently from a tailplane aircraft. The accelerations calculated in the foregoing are those measured at the aircraft's cg. Accelerations at the aircraft's extremities may be much greater due to added yawing, rolling and/or pitching motions and they will also affect the control surfaces. 6.7.3 Surface gusts or low-level wind shear Gust ratios In normal flying weather the velocity of any near-surface wind is changing constantly. Due to the eddies that usually exist within the flow, fluctuations in direction of 20° or so and in speed perhaps 25% either side of the mean, occur every minute. In other than very light wind conditions these variations are evident in the form of wind gusts. In stronger wind conditions, gust ratios (maximum gust to mean wind speed) are typically 1.6:1 over open country and 2:1 or greater over rough terrain, adding more turbulence to the flow. In an unstable atmospheric boundary layer the rising air in thermals is complemented by colder air sinking from the top of the layer, where the wind velocity approximates the gradient flow; i.e. the direction may be backed by 20–30° from the wind at the surface, and the speed is greater. The descending air retains most of these characteristics when it arrives at the surface as a strong gust, thus backing (i.e. shifting anticlockwise around the compass) and increasing in speed. Very light aircraft are of course more susceptible than others to low-level gusts. Such gusts figure in light aircraft accidents perhaps ten times more often than all other forms of windshear or turbulence combined. However, such upsets don't often result in serious injury to the occupants, and coping with such conditions in take-off and landing is an everyday part of pilot development. This module is concerned with more unusual events. Horizontal shear effects Horizontal shear is the change in horizontal wind velocity (speed and/or direction — gusts and lulls) with horizontal distance flown; i.e. a substantial change in the ambient energy state of the air mass in which the aircraft is borne. Horizontal shear is particularly dangerous when landing, taking off or going around as headwinds can suddenly disappear or change to strong crosswind gusts. These can last anywhere from a few seconds to several minutes. Crosswinds can change to tailwinds, resulting in loss of control and ground collision. There are two general classifications for horizontal shear. Increasing-performance shear. If a low-flying aircraft suddenly encounters an increase in the headwind component of wind speed (or a decrease in a tailwind) then due to its inertia the aircraft will momentarily maintain its speed (and flight path) relative to the Earth. Thus there will be a brief increase in speed of flow over the wings with consequent increase in lift. The aircraft will rise, gaining potential energy, until the inertial effects are overcome and the aircraft restores itself to the previous flight state at a higher altitude than previously; but at a changed ground speed and track — if the changed wind velocity is maintained. Decreasing-performance shear. Similarly should the aircraft encounter a decrease in the headwind component (a lull, or a gust from the rear) then airspeed and lift will decrease, and the aircraft will sink until the inertial effects are overcome. In recreational light aircraft flight conditions (and in accordance with the lift equation) the percentage increase or decrease in lift will be about double the percentage increase or decrease in airspeed; i.e. if airspeed dropped by 10% then lift will drop by 20% and the aircraft will sink very quickly. The worst situations to encounter such shear are where loss of airspeed and/or a sudden loss of height, take-off or climb performance could be critical — on the final approach to landing, on take-off or during a go-around . The time taken for the aircraft to restore itself to the original airspeed will be much the same as that taken to gain — in normal conditions — the same increase in airspeed by increasing power. Usually increasing-performance shear should not present any problem to an aircraft on approach or take-off, as long as the pilot continues to maintain the appropriate attitude in pitch, ignoring the speed increase(s), and is prepared for a possible decreasing-performance shear encounter to follow. On the other hand decreasing-performance shear will be very dangerous if the aircraft has insufficient height to clear obstacles while the pilot takes action to accelerate the aircraft through the shear and minimise height loss. If the aircraft's initial airspeed was less than the safe speed near the ground, including the normal 50% gust estimate allowance, then the shear effect is exacerbated and the rate of sink could be extremely high. Wind shear occurring just after wheels-off can cause the aircraft to stop accelerating. Wind shear events are usually a combination of wind speed variations and variations in three-dimensional direction, which will affect aircraft speed, angle of attack and attitude in the three axes. Thus encountering changes in horizontal flow within the airmass causes momentary changes in lift. There are consequent variations in the vertical profile of the flight path plus — with significant wind direction changes — diversions from the planned ground path and uncommanded motions in roll, yaw and pitch. Increasing-performance shear could even stall the aircraft: imagine an aircraft in slower level flight encountering a 20-knot gust vector at 45° to the horizontal. The effect would be like encountering a 14-knot head-on gust combined with a 25 fps updraft — the airspeed would be increased but the vertical gust component could take aoa past critical, so we have an accelerated stall. Something you can be sure of is that no matter what scientists and aviators may do to place wind shear and turbulence events into tidy boxes, the atmosphere has never been a party to such classification and will, on occasion and literally out of the blue, produce a demonstration of staggering power that just confounds our experience and expectations. Various scenarios were outlined in the 'Don't stall and spin in from a turn' module where the aircraft could be flying with little margin between effective and critical aoa; it is on occasions like these that Murphy's Law springs into action. What can and will go wrong at those worse possible times is an encounter with wind shear or turbulence that suddenly increases the effective aoa of the wing and instantly switches on a stall/spin event or a high sink rate at the worst possible time. Vertical shear (unrelated to vertical gust shear) is the term used for the change in the roughly horizontal wind velocity with change in height; i.e. as the aircraft is climbing or descending. As the vertical component of a light aircraft's velocity during climb or descent is probably no more than 12% of its horizontal velocity, the outcome of vertical shear is much the same as that for horizontal shear so we'll ignore the term and talk about the wind gradient. The wind gradient The Earth's surface has a frictional interaction with the atmosphere. Its effect decreases with height, until between 1500 and 3000 feet agl the gradient wind (i.e. the wind more or less is aligned with the isobars on the meteorological surface chart) dominates. The stability of that 'friction' or 'boundary' layer between the surface and the gradient wind level affects the strength of the friction force. A very stable layer suppresses turbulence and friction is weak except near the surface. In a superadiabatic layer convective turbulence is very strong and the friction force will be strong. In a typically neutral layer, with a moderately strong gradient wind of about 30 knots at 2500 feet, the wind speed might be 20 knots at 750 feet but only 10 knots at the surface. There is also a change in wind direction within the layer, perhaps as much as 40°. The rate of change in the gradient wind speed is generally more pronounced within the lower 300 feet, while the change in direction in that first 300 feet is negligible in strong winds but greatest in light winds, perhaps as much as 15–20° if the surface wind is less than 5 knots. The profile of the wind velocity change between the gradient wind and the surface wind is called the wind gradient. The greatest change in wind gradient velocities occurs at night and early morning. If the gradient wind speed is 30 knots at 2500 feet agl and reduces uniformly to 10 knots at the surface then, although the 20-knot change is relatively high, the time taken for a light aircraft to descend for landing through that wind profile is measured in minutes; thus there is no shear because the rate of change is slow. Remember in aviation terms wind shear is a sudden but sustained 'variation in wind along the flight path of a pattern, intensity and duration, that displaces the aircraft abruptly from its intended path and sufficiently that substantial and timely control action is needed.' So the average recreational light aircraft is not adversely affected by the normal (see Note 3) wind gradient provided that the minimum safe speed is maintained during take-off and landing, and the pilot remains aware of the gradient effects on the flight path/speed profile, adjusting the usual piloting techniques accordingly. (Note: 'normal' for the average recreational light aircraft implies a surface wind no more than 'moderate'; i.e. less than 16 knots or the point at which a dry '15 knot' windsock becomes horizontal. Greater surface wind speed could indicate a more pronounced gradient and thus possible shear conditions within the gradient.) 6.7.4 The speed to fly in turbulence Vno — maximum structural cruise speed In light aircraft the green arc on the airspeed indicator should indicate the 'normal operating' range between Vs1 at the lower limit, and Vno, or perhaps Vc, at the upper limit. Vno is the maximum structural cruise speed and, when cruising at and below Vno, the airframe would not be put at risk of overstressing in an encounter with turbulence in the upper end of the moderate range. Flight in the yellow arc speed range between Vno/Vc and Vne should only be conducted using controls cautiously and in reasonably smooth atmospheric conditions. Vc — design cruising speed Vc is normally not a limiting speed — it is a value chosen by the designer as a basis for stress calculations. In the FAR Part 23 regulation normal category, Vc in knots may not be less than 33 times the square root of the aircraft wing loading in pounds/square feet. For example 'minimum' Vc for an aircraft with 9 lb/ft² weight/wing area ratio (about 45 kg/m²) would be 33 × 3 = 99 knots. Alternatively the designer is allowed to obtain a lower speed value by setting Vc at 90% of Vh — the maximum level flight speed attainable at sea level whilst utilising maximum continuous engine power. Vno must not be less than the minimum Vc and for light aircraft Vc and Vno can be considered synonymous. The representative gust envelope, below, for a normal category aircraft superimposes positive and negative vertical gust load lines over a manoeuvring V-n diagram similar to that shown in the 'Airspeed and properties of air' tutorial. The horizontal light blue line indicates airspeed increasing from zero. The calculated gust load lines originate at the normal flight load condition of +1g, the strong 50 fps (30 knot) gust line extending to Vc and the moderate 25 fps (15 knot) line extending to Vd (the design diving speed). You can see that the moderate line intersects with Va at about 2g (i.e. a 1g acceleration) and with Vc at about 2.8g (a 1.8g acceleration). The strong gust line intersects with Va at about 3g and with Vc at something in excess of the 3.8g limit load. The brown arrow shows the 2.5g load — added to the normal 1g load — when the aircraft, flying at a speed about 30% higher than Va, encounters a 50 fps updraught. The total load factor is then about 3.5g; within the limit load factor, even though the gust is at the low end of the strong gust category. The pink arrow shows the resultant 2g load when the aircraft, flying at a speed about 30% higher than Vc, encounters a 25 fps updraught. Adding the normal 1g load the total load factor is then 3g. So even when flying at a speed somewhat greater than Vc/Vno in a certified light aircraft, an encounter with a vertical gust at the low end of the moderate gust range would be no problem. The calculations designers use to establish the gust load lines is similar to those used in the preceding section 'Vertical gust effects' but more refined; e.g. using a 'gust alleviation factor' rather simplifying the calculation with the concept of a 'sharp-edged gust'. FAR 23 Appendix A provides simplified design load criteria and allows designers of many conventional single-engine monoplanes weighing less than 2700 kg to take advantage of the simplification. That same appendix is generally duplicated in the design regulations of most other countries. One advantage of interest to us is that it is not necessary to specify Vno; instead, Vc is designated in the flight manual as the maximum structural cruise speed (i.e. Vno = Vc) and that Vc is probably set at 90% of Vh, as mentioned above. Va — design manoeuvring speed Almost all recreational light aircraft are built to simplified design standards that may not include rational consideration of gust loads — and there is no requirement for designers to publish a 'turbulence penetration' speed. For such aircraft, the maximum speed in anything approaching rough air is the design manoeuvring speed, so aircraft flight manuals or Pilot's Operating Handbooks nominate Va, which is usually considerably lower than Vc, as the speed to fly in 'turbulence'. There are other advantages in nominating the lower speed; e.g. most pilots have difficulties in classifying the turbulence being experienced (one pilot's 'moderate' may be another's 'extreme') and in controlling an aircraft in even moderate turbulence without experiencing considerable variation in speed. So rather than nominating a 'rough air' speed or a 'turbulence penetration' speed, manufacturers specify Va as the 'speed to fly' in turbulence. Before going further, we should examine how Va is derived. At higher speeds the wing lift coefficient (i.e. the aoa plus flap/slat/spoiler configuration) is relatively low, with much of the lift being provided by the dynamic pressure due to the airspeed — so the lifting force potential of the wing is very high. In these circumstances the wing loading might be readily tripled or quadrupled through abrupt and excessive elevator movement. For example if the aircraft was flying with CL = 0.25 and the pilot suddenly pulled back hard on the stick then CL might increase to 0.75 applying a momentary 3g load made up of the pre-existing 1g normal load plus the 2g acceleration. So it is unwise to make full or abrupt applications of any one primary flight control if flying at a speed greater than Va. This is because at the higher speeds it is easy to apply forces that could exceed the airframe structural limitations, and particularly so if you apply non-symmetrical loads; e.g. apply lots of elevator and rudder together. Misuse of controls in light aircraft at high speed can generate greater structural loads than those likely to be encountered in turbulence, so Va is also useful as a 'turbulent air operating speed'. At this compromise speed the aircraft will produce an accelerated stall, and thus alleviate the aerodynamic load on the wings, if it encounters a vertical gust imparting an acceleration sufficient to exceed the load limit factor. Aircraft design rules generally state that the minimum acceptable manoeuvring speed is a fixed calculation relative to Vs1 for all aircraft within the same category; for a normal category light aircraft (whose certificated vertical load limit factor is +3.8g) minimum Va = Ö3.8 Vs1 or 1.95 × Vs1. Of course the aircraft designer may specify a Va speed that is greater than the minimum requirement. The sample gust envelope diagram indicates that particular aircraft at Va could handle a vertical gust speed greater than 50 fps without reaching the load limit. All the preceding assumes the airspeed indicator has been properly calibrated and Va is stated as a calibrated airspeed. If it has not been accurately calibrated each one knot error in IAS around Va speeds will make a 0.1g difference in wing loading; i.e. if the ASI is understating airspeed by 10 knots then the load is 1g greater than thought. For more Va information see 'Critical limiting speeds'. What speed then? Follow the recommendations in the manufacturer's approved documentation. However, if that lacks substance then the following is relevant. If in cruising flight at speeds at or below Vno/Vc and 'very low' to 'low' turbulence is encountered, speed could be maintained without detriment, but be prepared to slow down if you suspect it may become rougher or if conditions suit the development of fast-rising thermals. If turbulence is in the moderate to severe category, reduce speed to the weight-adjusted Va. If flight at this speed is still worrying then speed could be reduced further. But when flying in moderate to severe turbulence at speeds below the weight-adjusted Va, then although the potential for exceeding load limits is no longer a problem, the potential for loss of control is much increased. As speed is reduced below Va updraft encounters produce increasing changes in aoa. This increases the potential for stall and in rough conditions even transient stalls may lead to longer-term loss of control with possible spin entry — and spins in severe turbulence may not be quickly recoverable. Loss of control may also lead to airspeed exceeding Va and thus restoring the potential to exceed load limits. Normal minimum safe speed in fairly smooth air is 1.5 × Vs1, but in very rough conditions the lower limit should be perhaps 1.7 × Vs1. You can see from the V-n diagram that the intersection of the 50 fps gust line and the Cna curve corresponds with a load factor of about 2.8g. The stall speed is escalated by the square root of the load factor and the square root of 2.8 = 1.7. If there is no manufacturer's documentation or instrument panel placard indicating manoeuvring speed, or a speed to fly in turbulence, then assume maximum weight Va is twice Vs1 CAS. If weight is below MTOW reduce Va by one half of the percentage weight reduction; e.g. if weight is 16% below MTOW, reduce Va by 8%. In addition it should be recognised that some sport and recreational light aircraft are ageing, the strength of their airframe components is not 'as new' and the designed ultimate load limit factor is no longer achievable. 6.7.5 Coping with shear and turbulence Prudent actions The action to take in encounters with turbulence or shear very much depends on your interpretation of events. For example if, in cruising flight, you believe you have entered just a limited layer of turbulence then you would initiate a shallow descent or climb to find smoother air. At the other extreme is a cruising flight encounter with a severe vertical gust or other severe turbulence, where your actions might be: set and tighten the engine control(s) to provide power appropriate to the Va target and then try to hold a straight and level attitude — if it's really rough you might need both hands on the control column tighten harnesses; you should not have any loose objects in the aircraft. don't chase the airspeed indicator (which may well be giving transient erroneous indications anyway), just hold the attitude as much as possible. (If turbulence is really rough it may be impossible to read the instruments, not least perhaps because your eyes are not able to refocus quickly enough.) don't over-react to changes in altitude avoid adding any manoeuvring loads such as those that are applied if you attempt a 180° turn; and certainly don't make abrupt asymmetric manoeuvres. Do not extend flaps, as in most light aircraft the effect is to reduce the structural limit load factor, full flap usually by about 50% to around 2g. If controllability is becoming difficult and the aircraft has retractable undercarriage then lower it — the drag reduces higher speed excursions and the lower drag line seems to reduce yaw. After escaping turbulence do not retract the undercarriage; inspect the area for damage immediately after landing. In excessive uplift, rather than going with the flow it may be prudent to reduce power and lower the nose somewhat to maintain target speed. It depends on what is above you — a towering cumulus or Class C airspace for example. If you are likely to violate controlled airspace notify Flight Service on the area frequency and ensure the transponder, if available, is operating. If you have the ability, then inform Flight Service of the turbulence encounter and location — the pilot report may help others to avoid it. Generally an aircraft will not run into a severe downdraft at low levels, more likely it will meet the turbulent low-level horizontal outflow from the downdraft. However, if you encounter a severe downdraft at lower levels, the only option is to immediately apply full power and either adopt the attitude for best rate of climb or allow airspeed to increase even beyond Va and trust you will fly out of the downdraft quickly. Whichever way the pilot is in a hazardous situation, and the aim should be to recognise and avoid extreme shear conditions. Upset recovery Many windshear or turbulence encounters will result in an uncommanded roll perhaps combined with strong yaw, pitch-up or pitch-down. The result may well be an aircraft in a most abnormal attitude and losing height fast. Such events are very dangerous at low level. Most light aircraft don't have much roll capability, perhaps 15–30° per second is the norm. If a condition such as a curl-over, a lee wave rotor or the wing tip vortices from a preceding larger aircraft (for example when turning base to final following a larger aircraft landing from a straight-in approach), is encountered, the resulting induced roll may well exceed the countering capability of the ailerons. As mentioned in the 'Engine failure after take-off' module under the sub-heading 'Unloading the wings is a good practice to practise' a light aircraft (but not a trike) can be better controlled for at least a few seconds, even at sub-Vs speeds, by pushing forward to unload the wings so that the aircraft is operating in the reduced-g zone (between perhaps +0.25g and +0.75g) but not in the negative-g zone'. In the 'Don't stall and spin in from a turn' module under the sub-heading 'When I recognise a stall with wing drop what's the best way to recover?' a stall recovery technique was presented. That same technique is applicable to recovery from an abnormal attitude (where the primary aim is to get all lift force directed away from the ground), except that the initial forward stick movement should unload the wings rather than just reducing aoa below critical. Centralise the ailerons and unload the wings to a reduced-g level, even if steeply banked or inverted. This may be a difficult decision if the nose is already pitched down and not much height is available, but certainly keep the stick forward of neutral. Increase power smoothly, up to maximum if low and slow, but if the nose is pitched down and speed is above or accelerating towards Va then reduce power. Don't wait for the engine to fully respond before moving to the next actions. If the aircraft is inverted, then close the throttle to improve subsequent responsiveness. Cancel any yaw with rudder, and centre the slip ball. This and the two preceding items should be near-simultaneous actions. While maintaining the low wing loading, roll the wings level with aileron so that all the lift force will be directed away from the ground, and use coordinated rudder to assist the ailerons. If near inverted, choose the roll direction that provides quicker return to a wings-level attitude but if the ailerons can't counter the induced roll then you might take advantage of the roll momentum and continue to roll through. As the wings are nearing level, ease the stick back to the neutral position, or just aft of it, to correct the attitude in pitch. When safe, adjust attitude and power as necessary for the climb-out. If on an approach to landing, then go around — and take your time starting the next approach. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

6.6.1 Why the high fatality rate? Loss of control The primary causal factor for the generally high fatality/severe injury rate is loss of control in a mistimed/poorly executed initial turn, perhaps being intimidated by terrain/obstructions; or, following a successful 180° turn, realising too late the airfield can't be reached resulting in an unplanned, perhaps desperate, reaction. The factors involved in loss of control events were discussed in the article 'Don't stall and spin in from a turn'. Here's an extract from an RA-Aus accident report compiled by a qualified witness on behalf of the severely injured pilot. At the time, the pilot had a CPL and RA-Aus Pilot Certificate but only 2 hours experience in his Supercat CAO 95.10 aircraft. The crash occurred from a 900-metre runway at an airfield in mountainous terrain, at an elevation of 3300 feet. At the time, wind was light and variable with no turbulence, and temperature corresponded to the ISA norm. Apparently partial loss of thrust was experienced on take-off. " The aircraft took off normally ... climbed to 150–200 feet near the end of the runway ... then appeared to sink and turn left ...(there is a power line 300 m past the runway end, below runway level in a ravine)... the angle of bank increased rapidly until it appeared to be almost 90°. The aircraft descended rapidly and disappeared behind some trees followed by a surprisingly soft 'crump'." The aircraft hit the ground almost vertically. 6.6.2 Opting for the turn-back The need for a properly derived decision The conventional and generally long-accepted wisdom in the event of a low-level off-field failure is for a properly controlled landing — hopefully into wind, more or less straight ahead, but certainly somewhere within 60° either side of the initial path. Factors involved were examined in the three preceding modules of this series. If the engine fails well into the climb-out one of the possible options is to turn back and land on the departure field. If the take-off and climb was into wind and a height of perhaps 1500 feet agl had been attained (and the rate of sink is less than the rate of climb) then there would be every reason to turn back and land on that perfectly good airfield. There may be sufficient height in hand to manoeuvre for a normal, but close, circuit; or otherwise a crosswind, rather than a difficult downwind, contra-traffic landing. On the other hand there will be a minimum 'decision height' below which a turn-back for a landing in any direction could clearly not be accomplished; and of course there will be an associated maximum distance. The only logical basis for opting for a turn-back, rather than landing somewhere within that 120° arc ahead of you, is a properly derived decision that it is by far the safest choice. This requires knowledge of the dynamics involved in the turn-back and of the relevant characteristics of the aircraft being flown. Knowledge of the latter can only be gained by practising accurate, low-speed, fully banked gliding turns at a safe height and measuring the height lost in the turn plus the distance:height ratio at Vbg. 6.6.3 Turning back — procedure and dynamics The repositioning manoeuvre Turning back to land on, or parallel to, the departure runway is a two-stage procedure. This comprises a repositioning manoeuvre, turning through maybe 210°, so that the aircraft is positioned as close as possible to the extended runway line at sufficient height to then glide directly back to the planned touchdown point at Vbg — the speed that provides the best L/D ratio and thus optimum distance in a straight glide. A small turn will be needed to finally align with the selected landing path. If the take-off has a crosswind component, the initial turn should be conducted into the crosswind so that the aircraft will drift towards the extended runway line and also reduce the ground diameter of the turn a little. If the take-off has been downwind because of runway slope then the minimum height for a turn-back would be greatly increased; if there are any doubts don't turn back — except as needed for an into-wind off-field landing. Of course there is no need to opt just for a runway if you have departed from a larger airfield with ample cleared area available for an emergency landing. While repositioning, it is important to minimise the time spent in the turn and thus the height loss, so gliding at Vbg or even Vmp is not a requirement; but choice of an optimum turn speed is vital. Turn speed, diameter and rate of turn The air radius of a turn is directly proportional to the true airspeed squared and indirectly proportional to the angle of bank. The rate of turn is directly proportional to the angle of bank and indirectly proportional to the speed. Table 5.1 shows some calculations for various bank angles at speeds of 40, 50, 60 and 70 knots. The calculations are based on two slightly simplified but accurate equations applicable to all light aircraft: The turn diameter (metres) = the airspeed (metres per second) squared divided by 5 × the tangent of the bank angle. Example: airspeed 60 knots (30 m/sec), bank angle 30° and tangent 30° is close to 0.6. Turn diameter = 30 × 30/5 × 0.6 = 900/3 = 300 metres. The rate of turn (degrees per second) = the tangent of the bank angle × 1100 divided by the airspeed in knots. Example: bank angle 45°, tangent 45° is 1.0 and airspeed 40 knots. Rate of turn = 1.0 × 1100/40 = 1100/40 =28°/sec. So time to turn through 210° = 8 seconds. Note 1: a rate 1 turn is 3°/sec, a rate 2 turn is 6°/sec, a rate 3 turn is 9°/sec, and a rate 4 turn is 12°/sec. Very heavy transport aircraft normally turn at 1.5°/sec. Table 5.1 Turn diameters and turn times Airspeed (knots CAS) Bank angle Tangent Turn diameter (metres) Turn rate (°/sec) Time to turn through 210° (seconds) 40 10° 0.2 400 m 5 42 s (20 m/s) 20° 0.4 200 m 11 19 s 30° 0.6 135 m 16 13 s 45° 1.0 80 m 28 8 s 60° 1.7 45 m 48 4 s 50 10° 0.2 625 m 4 53 s (25 m/s) 20° 0.4 310 m 9 23 s 30° 0.6 210 m 13 16 s 45° 1.0 125 m 22 10 s 60° 1.7 73 m 38 6 s 60 10° 0.2 900 m 3.7 57 s (30 m/s) 20° 0.4 450 m 7.4 28 s 30° 0.6 300 m 11 19 s 45° 1.0 180 m 18 12 s 60° 1.7 105 m 32 7 s 70 10° 0.2 1225 m 3.1 67 s (35 m/s) 20° 0.4 610 m 6.3 33 s 30° 0.6 410 m 9 23 s 45° 1.0 245 m 16 13 s 60° 1.7 140 m 27 8 s It can be seen that both a greatly reduced turn diameter and a very fast turn rate are achieved at the lowest speed coupled with the highest bank angle, with the bank angle being more significant than the airspeed. So the stall speed of the aircraft has some importance; the ultralight with a very low Vs1 can produce a very fast small diameter turn. Note from the table that at all speeds the time to turn through 210° and the air diameter of the turn are around four times better with 60° bank than with 20°. However, the third factor to be considered when selecting the bank angle and airspeed is the rate of sink relative to the bank angle. Bank angle, stall speed in the turn and rate of sink The 'turn forces' diagram shows the relationships between total lift force, bank angle, weight and the centripetal force required to make the turn. In the turn, the vertical component [Lvc] of the total lift force just about balances aircraft weight, and the horizontal component of lift [Lhc] provides the centripetal force to minimise the turn radius. At 30° bank angle Lhc = 0.6 Lvc while at 60° Lhc = 1.7 Lvc. So to provide the centripetal force for a sustained turn, the wing loading must be increased by pulling g as angle of bank increases; rather slowly up to a bank angle of 30° — where it is 15% greater than normal level flight loading — after which it escalates. The diagram is for a powered level turn, but the principles are much the same for a gliding turn. Except that in the level turn, the airspeed is generally held constant and the increase in total lift force is gained by increasing angle of attack; the consequent increase in induced drag is countered by increasing thrust. In a gliding turn the increase in total lift force is obtained by both increasing the angle of attack (pulling g) as bank increases and increasing the airspeed by lowering the nose; the rate of sink accelerates as airspeed and aoa (thus induced drag) increase. Table 5.2 is a sample profile of the increase in sink rate in a sustained gliding turn at particular bank angles. The base sink rate is the minimum sink achievable in a straight glide at Vmp. The fourth column shows the increase in turn stall speed and the last column is a representative estimate of the increase in rate of sink in the turn if the airspeed chosen was about 10% higher than the turn stall speed [i.e. for 45° bank airspeed = 1.3 Vs1]. Note: L/D or glide ratio [actually Lvc/D] deteriorates markedly as bank angle increases because of the escalating induced drag as more g is pulled. Table 5.2: stall speed/sink rate in a sustained gliding turn Bank angle Cosine Load factor (=1/cos angle) Vs1 multiplier (increase) Sink rate multiplier (See note 1 below) 10° 0.98 1.02g 1.01 (+1%) 1.05 (+5%) 20° 0.94 1.06g 1.03 (+3%) 1.15 (+15%) 30° 0.87 1.15g 1.07 (+7%) 1.3 (+30%) 45° 0.71 1.41g 1.19 (+19%) 1.9 (+90%) 60° 0.50 2.00g 1.41 (+41%) 3.5 (+250%) Note 2: the comparative sink rates shown in the right-hand column will vary substantially with each aircraft type/model. The late Tony Hayes of the Thruster Operations Support Group kindly produced some Thruster T300 trial data, which showed that in a 45° bank gliding turn at 55 knots (1.3 Vs1) the sink rate was 900 fpm, or 3 times the Vmp sink rate of 300 fpm. If the turn was conducted at 59 knots (1.4 Vs1) the sink rate increased to 1050 fpm or 3.5 times minimum sink in a straight glide. The sink rate in a straight glide at Vbg (48 knots) was 400 fpm. The trials were conducted soon after sunrise in a calm, stable atmosphere thereby providing best results. Sink rates would be worse in normal everyday conditions. Choosing the bank angle Obviously the height lost in the turn is a function of the rate of sink and the time spent in the turn. Table 5.3 is a calculation for a hypothetical ultralight that has a Vs1 of 40 knots and a minimum rate of sink in a straight glide of 420 fpm or 7 feet per second. The airspeed selected for the turn is just 10% greater than the stall speed (Vs[turn]) at those bank angles. Table 5.3 Height lost in a 210° turn. (Vs1=40 knots, minimum sink =420 fpm or 7 fps) Bank angle Vs (turn) +10% (knots) Turn diameter (metres) Turn time (seconds) Sink rate (fps) Height lost in turn (feet) 10° 44 540 m 46 7+ 330 ft 20° 45 280 m 24 8 190 ft 30° 47 190 m 15 9 135 ft 45° 52 135 m 10 13 130 ft 60° 62 110 m 7 24 170 ft It can be seen that a 45° bank angle, where Lhc = Lvc — i.e. the wing loading is equally distributed between countering gravity and providing the centripetal force — allows the least height loss. The height loss at a 30° bank angle is much the same but the lesser bank gives a larger turn diameter. Bank angles less than 30° or greater than 45° are not as efficient in terms of height loss. Similar relationships are found for other light aircraft, so 45° is the usually accepted optimum bank angle for least height loss and smaller diameter. The POH may recommend otherwise if high-lift devices are fitted. There is a problem with choosing and maintaining a particular bank angle, in that if the aircraft is not equipped for flight in instrument meteorological conditions there is no reliable instrumental means of accurately assessing the bank angle — though fortunately pilots tend to overestimate (rather than underestimate) the steepness of the bank by perhaps 10°, i.e. they believe they have 45° bank but in reality it is perhaps only 35°. The angle can only be confidently established by comparing the horizon with ascertained structural or cockpit angles. 6.6.4 Turning-back A possible scenario Imagine a competent aviator who has practised for steep turn-backs (at a safe height and maximum weight) and can hold the aircraft at constant speed with a constant bank angle known to be 45° and, by trial, has established the average rate of sink in such a turn. Vsi for the aircraft is 40 knots CAS and Vbg is 60 knots CAS. As a result, the pilot feels comfortable using an airspeed that is only 10% greater than the stall speed in a 45° banked turn — that speed is 52 knots and thus the average turn diameter is 135 metres, rate of turn is 21°/sec, and rate of sink is 900 fpm or 15 feet per second. Suppose that pilot takes off towards the north on a 600-metre north-south strip sited in rough terrain; there is nil wind and smooth ISA sea level conditions. The aircraft lifts off 200 metres from the southern end, climbing away at 60 knots (30 m/sec) and 500 fpm. The engine fails 60 seconds after wheels-off when the aircraft is 500 feet above airstrip level and 1800 m from the lift-off point, or 1400 m from the northern threshold. The pilot takes 4 seconds to react to the engine failure (see 'Engine failure after take-off') and decides on a turn-back. A further 5 seconds passes before the aircraft is established in the glide at the speed appropriate for the turn, i.e. 52 knots. The slow speed roll rate is around 15–20°/sec, so another 2 seconds passes before the turn is established. Thus about 10 seconds elapses between engine failure and start of turn. During this time the aircraft moves about 250 m further from the airstrip and loses perhaps 50 feet of altitude, so at start of turn the aircraft is 450 feet above runway level and 1650 m from the northern threshold. With a turn rate of 21°/sec and sink rate of 15 feet/sec, the 210° turn takes 10 seconds during which the aircraft loses 150 feet. So after straightening up and establishing descent at Vbg, the aircraft is 300 feet above strip level and a bit less than 1650 metres from the airstrip. So the elapsed time from engine failure to being in a position to start the straight line return glide is about 20 seconds, during which 200 feet of altitude is lost while the aircraft has moved nearly 250 m further from the runway. Let's presume the aircraft's L/D is 10:1, so to glide 1650 metres after straightening up it would have to start from a height of 165 m or 540 feet. Starting from only 300 feet it will hit the ground about 750 m short of the runway, so in this scenario the distance to glide after the end of the turn is of more importance than height lost in the turn. If the aircraft had taken off into a 10-knot (5 m/sec) headwind, then the end-of-turn point would be displaced 80 seconds × 5 m/sec = 400 m closer to the threshold, with then 1250 m to run. At the 60-knot Vbg and 70-knot (35 m/sec) ground speed descent the 1250 m would be covered in 36 seconds. The aircraft's L/D is 10:1 so the Vbg sink rate is 6 knots or 10 feet/second. Thus the aircraft will lose 360 feet during the glide indicating that, even with the favourable 10-knot wind, it will hit the terrain 200 m or so short of the threshold. The aircraft might just scrape in for a successful turn-back in nil wind conditions if the initial climb rate was such that it is 750 feet agl at 60 seconds after wheels-off, in which case it would be at 550 feet at end-of-turn. Choosing a safe speed Obviously you shouldn't conduct a low-level turn near the point of stall and any mishandling or turbulence during turns at high bank angles and low speeds may result in a stall-spin event, so a minimum safety factor for the turn must be considered. For a recreational light aircraft a factor of 10% above Vs[turn] may not be enough, so perhaps the turn speed should be 20% greater; i.e. 1.2 times Vs[turn]. For the example in the preceding scenario, that safer airspeed at the required 45° bank would then be 58 knots CAS — which might increase rate of sink from 15 to 17 feet/sec, the turn time from 10 to 11 seconds and thus the height loss in the turn from 150 to 190 feet; acceptable, considering the added safety. However, the stall speed at 45° bank is 1.2 × Vs1 CAS and multiplying that by 1.2 provides an airspeed of 1.44 × Vs1 CAS — close to our normally recognised safe speed of 1.5 × Vs1. So then considering all the inaccuracies inherent in flight we come back to 1.5 × Vs1 CAS (60 knots in the scenario) as the optimum speed in the 45° banked turn-back manoeuvre. Extract from an RA-Aus fatal accident report: 'Following the loss of power at approximately 300 feet, the pilot apparently attempted a turn to the left in an attempt to return to the runway that he had just departed from. At a position approximately 200 metres to the left of the extended centre line of runway 30 and 400 metres from the upwind threshold of that runway, the aircraft entered a spin and impacted the ground in a near vertical attitude. Note 3: In the preceding tables and text I have used the calibrated airspeed but the velocity in the equations should be the true airspeed, so the turn diameter will be greater than shown, the rate of turn will be less and consequently the height lost during the turn will be greater. 6.6.5 So what's the verdict? From the foregoing you might conclude that it would be foolish to state (though many do) that a return to the runway is possible if a particular aircraft type is above a certain height when EFATO occurs. The main factors to be considered/estimated in the very few seconds available for an informed decision are these: The distance you are from the nearest runway/airstrip threshold and the distance you will be when the 45° bank re-positioning turn, flown at 1.5 × Vs1 CAS, is completed and the aircraft established at Vbg. The estimated height still in hand after the repositioning turn is completed and whether that will be sufficient for the glide approach to the threshold. The effect wind and turbulence will have on the result. Although EFATO operations are near ground level the effect density altitude will have on the result must be taken into account. For example, as TAS increases with density altitude then the height loss during the turn at a particular CAS must increase. The existence of obstructions along the glide path. Possible collision avoidance risks in the contra-traffic landing — emergency, low-level, non-powered manoeuvring may lead to a stall/spin event. If very close to the airfield, can sufficient height be lost to land reasonably safely, taking wind effect into account. All of this indicates that the possibility of success is very difficult to assess quickly when airborne time remaining is rapidly counting down to zero. You must know your aircraft and your capabilities, and have previously established the safe turn-back performance under varying conditions. Also you must be a very good judge of distance (few pilots are) and be able to maintain absolute control at rather low energy levels and higher wing loadings; otherwise — it is most unwise to turn back! STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

Once airborne, naturally any engine failure is a failure after take-off even if the aircraft is 100 nm from the take-off point. However, the EFATO term is usually accepted to mean a significant loss of thrust occurring while the aircraft and pilot are still in 'take-off or go-around mode'. For example, haven't yet set course, or raised take-off flap, or haven't yet reached 1000 feet agl if intending to operate above that height, or, if doing circuits have not yet completed the crosswind turn; i.e. a 'thrust deterioration at take-off' that occurs while climbing soon after lift-off or during a go-around when the aircraft has little energy to trade. This module presumes the reader is familiar with the contents of the earlier 'Don't stall and spin in from a turn' and 'Don't land too fast in an emergency' modules, which are pertinent to this document. 6.5.1 What happens when the engine or propeller fails in the initial climb? Pilot and aircraft reaction times A recreational light aircraft established in the climb attitude at Vy (best rate of climb speed) has an aoa perhaps around 6–8°. At such angles there is significant induced drag so when thrust is lost, for any of a multitude of reasons, the aircraft may rapidly decelerate to stall speed — worse if the airframe also has much parasitic drag. The immediate action required is to convert the potential energy of height to a safer speed. When climbing at Vx (best angle or emergency climb speed) aoa could be around 8–12°, so deceleration following power loss is a greater hazard. Of course recreational light aircraft Pilot Certificate holders are aware of this and take immediate action to lower the nose to a position consistent with their estimate of the approach or glide attitude in pitch. Or do they? Material developed by the late Mike Valentine, the former RA-Aus Operations Manager and prestigious GFA stalwart, is included in this section. Mike conducted considerable research into pilot and aircraft reaction times following cable breaks in winched glider launches and engine failure after take-off in recreational light aircraft. Some research results — which were very similar for both aircraft categories — were published in the June 2004 issue of the RA-Aus journal, and are summarised as follows. Following an engine/propeller failure in the climb, there is an initial delay while the pilot's brain adjusts to the shock of the event and then she/he pushes the control column forward. This reaction time appears to average around three to five seconds, much longer than might be imagined, but similar results are obtained in tests by other aviation bodies. Mental paralysis/disbelief, i.e. 'this can't be happening?', is the main contributor to that delayed reaction; meanwhile the aircraft is slowing at perhaps 2 to 4 knots per second. It can be exacerbated by slight panic if the power loss is accompanied by very unusual engine noises, smoke and/or violent shaking. A quiet breakdown in the propeller speed reduction unit results in the unloaded engine's rpm increasing while the propeller is 'freewheeling' — producing no thrust — and it may take a little longer for the pilot to realise what has happened. If the aircraft is equipped with an effective elevator trim system and the pilot has trimmed for the climb speed — which is generally similar to the best glide speed — then the aircraft will of course try to regain its trimmed speed when thrust decreases; however, this takes too long to stabilise, and the pilot must take firm control and push the stick forward. As the pilot pushes over into the glide attitude the aircraft follows a curved flight path. During this manoeuvre, pitch attitude and wing loading are changing, and the aircraft still slows for two or three seconds before accelerating. When the desired attitude is eventually attained, the pushover is terminated and the aircraft is then apparently stable in its glide attitude. Apparently? Yes because, although the aircraft is in the required nose low attitude, it has just been through an energy-changing manoeuvre without the benefit of thrust to sustain it. Its inertia, aided and abetted by its drag, prevents it from immediately attaining the airspeed appropriate to the glide attitude; some seconds must be allowed for the aircraft to build to that speed. Gravity alone can't instantly accelerate an aircraft to a safe speed through a 10 or 15 degree pitch attitude change. The real EFATO event will be noticeably different from that experienced in a simulated EFATO because there is no residual thrust from an idling engine. If the propeller is windmilling there will be additional drag and thus a bit steeper descent path. Also the lack of a cohesive propeller slipstream over the tailplane will make the elevators feel different — and less effective. Any attempt to start manoeuvring the aircraft without allowing sufficient time for the indicated airspeed to build to, and stabilise at, a safe speed will risk loss of control — and don't think there is a discernible lag in the ASI; there isn't if it is in good condition and the pitot-static system is unobstructed. If the pilot lowers the nose to the glide attitude and immediately performs just a moderate 'bank and yank' manoeuvre, the aircraft may stall and spin. At least five seconds will elapse from the moment the pilot pushes the stick forward to the time the airspeed margin over stall is safe enough to carry out a gentle manoeuvre. The diagram below represents the result of Mike's tests in a simulated (and placid) EFATO when climbing at 55 knots (about 1.3 Vs of 42 knots). Similar results were found in other tests. The diagram doesn't show the 3–5 seconds reaction time for the average pilot, as the pilot for the test series was conditioned to an expectation of the throttle being pulled by the observer. During the pushover, the control column was pushed forward smartly enough and far enough to unload the wings to perhaps 0.5g or less, so that the aircraft is still totally controllable even if the airspeed reduces below the normal Vs1 of 42 knots. At 0.5g the airspeed will build relatively quickly because the lift will be nearer zero and thus induced drag is reduced to nearer zero. Unloading the wings is a good practice to practise As mentioned in the flight envelope section of the 'Don't fly real fast' article a light aircraft can be safely held at sub-Vs speeds for several seconds by unloading the wings so that the aircraft is operating in the reduced-g band between zero g and +1g, but not in negative g. The stall speed between +1g and 0g is still proportional to the square root of the wing loading g ratio, as indicated in Table 4.1. Table 4.1: stall speeds at positive loads below +1g Load factor Square root Stall speed knots +1g 1 42 +0.75g 0.86 36 +0.5g 0.70 30 +0.25g 0.5 21 0g 0 0 Note: when the wings are unloaded, ailerons and rudder can be used in ways that would be regarded as excessive at 1g loads. This unloading technique also has value as a stall recovery exercise (at a safe height) for pilots to really comprehend what is going on. It involves unloading the wings to perhaps 0.25g by pushing sufficiently forward on the control column so that you feel very light in the seat but not yet constrained in the harness as you would be if imposing negative g — or if dirt and dust start floating up from the floor. When unloaded — which takes an instant — roll the wings level (holding near zero g of course) using full aileron and whatever rudder is necessary (often quite a lot), and centre the aileron and rudder as soon as the wings are level. As drag at that minimum aoa is much reduced, speed will build more quickly and thus dive recovery is started earlier. With practice, the total height loss by taking such decisive action may be less than in a gentle reaction, and the speed will stay well within the allowable envelope in most recreational light aircraft. There will not be any fuel system problems as long as negative g is not applied. However, if forward pressure is slightly relaxed and the aircraft allowed to return to its normal 1g state while airspeed is below Vs1, the wing will promptly stall. 6.5.2 Practice good energy management in the take-off! Planned energy management during the initial climb Following engine failure in the climb, the total energy available is the sum of kinetic energy and potential energy of height. As shown above, a lot of that kinetic energy is lost to drag in the 6–8 seconds following loss of power. The potential gravitational energy must be converted to kinetic energy so that the total energy level of the aircraft is maintained, albeit at a lower level than that immediately prior to the power loss. There may not be enough time available to regain enough speed within the remaining height to have sufficient energy to arrest the rate of sink (i.e. flare) for a normal landing. A heavy or very heavy landing is then almost inevitable. For example, the low-momentum Thrusters and Drifters have thick high-lift wings that give their best climb rate [Vy] at about 50 knots. They probably need about 150 feet to build enough airspeed to enable the aircraft to be flared for a normal landing; obviously, more slippery aircraft need less height. The solution to this potential problem is planned energy management during the initial climb. Don't use the recommended speed for best rate of climb, use a climb speed perhaps 10–20% higher until at 200–250 feet, then steepen the climb a little to maintain Vy. The loss of initial climb performance won't be particularly significant but the additional speed in hand will make a difference if you lose thrust at a critical height. Of course, you may prefer to maintain the higher speed as a cruise-climb speed, particularly if there is a reasonable headwind or a tendency to overheat. What about using the best angle of climb speed for initial climb? Vx should not be used in normal operations — it should be regarded as an emergency climb speed. The high pitch attitude, high aoa and low speed provide a very limited safety margin if power is lost. If an airstrip is so marginal that you consider you must use Vx to clear obstructions at the end of the strip — or worse, out-climb rising terrain — then you should not be using that airstrip. If you absolutely have to use Vx for obstacle clearance then lower the nose to a safer climb speed as soon as possible. 6.5.3 Always be ready to implement plan B! Have a mental 'what if?" action plan Pilots must always be prepared for the possibility that the engine/propeller will lose thrust during the take-off and climb out (or at any other time during flight), and have simple pre-formulated mental action plans for the particular airfield/strip/runway conditions and various failure modes — remembering that, depending on height if the engine fails, there may be little time to do much else but keep your eyes outside the office, select the landing run and fly the aeroplane. One thing though — it is important to close the throttle early enough to avoid the engine suddenly regaining full power at an inopportune time; e.g. just as you are about to flare, thus driving the aircraft into the ground — which has happened on occasion. If there is any thought that something is not quite right during taxying, run-up or the take-off ground roll, the flight should be abandoned immediately. A surprising number of pilots disregard indications/warnings that something is not as it should be and press on to an inevitably expensive reminder that engine/fuel/propeller problems cannot fix themselves. It'll be okay? Not likely! On-field landing If the aircraft is very low when the engine fails the only option is to keep the wings reasonably level, the slip ball centred and land more or less straight ahead. So the minimum action plan would be: If loss of thrust or other problem is evident, immediately push over into the approach attitude while keeping the slip ball centred. If loss of thrust is accompanied by extreme vibration or massive shaking of the aircraft (possibly due to a propeller blade failure), it is important to immediately shut down the engine to avoid it departing from its mountings. Do nothing else while waiting the few seconds for the aircraft to stabilise at a safe speed — except hold that attitude, keep your eyes outside and decide the landing run; probably there will be little time or opportunity to conduct any cockpit or radio drills prior to touchdown. Ensure the throttle is closed, lower full flap or sideslip if height permits, then land the aircraft. Be careful to avoid wheelbarrowing. Brake hard and/or ground loop if necessary to avoid collision. The groundloop is induced by booting in full rudder (and brake) on the side to which you want to swing and will probably result in some wing tip, undercarriage and propeller damage, unless you impact something other than the ground. Running it into long grass will help slow the aircraft. There have been occasions, even at small airfields, where a recreational light aircraft losing power at 200 feet or less had sufficient height to safely turn 60–90° and land on, or parallel with, an intersecting strip. Of course, the pilot in those reported cases has been quite familiar with the aircraft's capabilities and had commenced take-off with little or no runway behind. Off-field landing If some height has been gained but there is no possibility of landing on the airfield, then an off-field landing is mandatory. Look for somewhere to put it down but don't immediately fix on the first likely landing site spotted straight ahead of you — there may be a more suitable site closer. However, you have to rapidly assess your height and airspeed (i.e. your energy level), and the turn possibilities available; i.e. can you safely turn through 30° or 45°, perhaps 60°, and still make it to that much better looking site? Will the wind assist or hinder? How much height will be lost in the turn? It has to be a quick decision because at best you have just a few seconds available to plan the approach. If any doubt go for 'into wind' and remember you can't stretch the glide! Do not choose the site at marginal distance, even if it's perfect. Close by is better because the height in hand can be used for manoeuvring the aircraft into the best approach position. Because you have no power available you must always have an adequate height margin to allow for distractions, misjudgements, additional loss of height in turns, adverse wind shifts, sinking air, turbulence and other unforeseen events — and you can dump excess height quickly using full flap or sideslipping. Remember that the rate of sink whilst sideslipping is high and the slip must be arrested before the flare. Some major factors affecting the outcome of a forced landing are highlighted in the previous module 'Don't land too fast in an emergency' and it is not my intention to list all factors that might be assessed in the decision making process following EFATO. Suffice to say, it is impossible to assess everything in the few seconds available, hence the need for prior knowledge of the airfield environs, plus a pre-established plan B and intuitive procedures for any situation that may occur before you are established at a safer height. Apart from being clearly within range the choice of landing site is affected by: wind strength and direction ground run availability and direction; a short into-wind site may be preferable to a longer but crosswind/downwind site for an aircraft with a low stall speed; the reverse applies for an aircraft with a high stall speed. It all relates to kinetic energy and stopping distance approach obstructions; final approach may require some diversion around/over trees, under/over power-lines plus avoidance of other obstructions. Can the near-ground turns be handled safely? Is there sufficient margin for misjudgement and/or wind gusts? ground surface and obstructions, including livestock, during the ground roll. Can you steer to avoid them? Are livestock or kangaroos likely to take fright and run into your path? the energy absorbing properties of the vegetation ground slope: the possibilities of landing downslope may range from difficult to impossible; moderate upslope is good if the pre-touchdown flare is well judged. There is a much greater change in the flight path during the flare; for example, if the upslope has a one in six gradient (about 15°) and the aircraft's glide slope is 10° then the flight path has to be altered by 25° so that the aircraft is flying parallel to the upslope surface before final touchdown. A higher approach speed is needed because the increased wing loading during the flare (a turn in the vertical plane) increases stall speed. If the wind is upslope then a crosswind landing may be feasible if a rural road is chosen can you avoid traffic, larger trees, drainage ditches, wires and poles, particularly in a crosswind situation? a final approach into a low sun should be avoided so that vision is not obscured. All of this is impossible to assess in the few seconds available, hence the need for prior knowledge of the airfield environs and a pre-established emergency procedure for any situation that may occur before you are established at a safe height. As height increases, the options increase for turning towards and reaching more suitable landing areas, making a short distress call and doing some quick trouble shooting. Trouble-shooting When trouble-shooting full or partial power loss remember the first edict — constantly 'fly the aeroplane!'. If the engine is running very roughly or died quietly (i.e. without obviously discordant sounds associated with mechanical failure) and time is available, then apart from the engine gauges, the obvious things to check or do are: Fuel supply: switch tanks (making sure you haven't inadvertently switched to the 'fuel off' position), fuel booster pump on, check engine primer closed. Air supply/mixture: throttle position and friction nut, throttle linkage connection and mixture control position. Apply and maintain carburettor heat (while engine is still warm), setting the throttle opening at the normal starting position. Apply carburettor heat or select alternate air to bypass the air intake filter — which could be blocked by grass seeds or a bird strike. Ignition: position of ignition switches — and try alternating switches in case one magneto is operating out of synchronisation. Or: reverse the last thing you did before the engine packed up. And then: try a restart. There is no point in continuing with a forced landing if the engine is really okay. Cockpit check prior to touchdown Pilot and passenger harnesses must be tight and maybe remove eyeglasses. Seats should be slid back and re-locked in place (if that is possible without adding to the risk) but be aware of the cg movement. Advise the passenger of intentions, warn to brace for impact and advise evacuation actions after coming to a halt. Unlatch the doors so that they will not jam shut on impact. If the aircraft has a canopy or hatch take similar safety action, if that is possible without the canopy affecting controllability or detaching and damaging the empennage. If equipped with a retractable undercarriage, leave the wheels down unless surface conditions indicate otherwise. To minimise fire risk turn the ignition, fuel and electrics off. It is important to research and develop your own safety plan, including the cockpit and radio drills, so that it is more deeply ingrained and appropriate to your capabilities and the aircraft being flown. Don't just adopt a plan published by someone else. Before moving onto the runway for take-off, do a mental rehearsal of plan B; such rehearsal is a powerful safety aid. As height achieved before engine failure increases, the options increase for trouble-shooting, turning towards and reaching more suitable landing areas; making a distress call on a selected frequency; properly securing the fuel, ignition and electrical systems; and for an adequate cockpit check prior to touchdown — but all in accordance with the plan. Partial thrust loss If the engine/propeller does not fail completely but is producing sufficient thrust to enable level flight at a safe speed then, if you can't determine the fault, it may be possible to return to the airfield. Make only moderate turns, maintaining height if possible without the airspeed decaying, and choose a route that provides potential landing sites in case the engine loses further power. It's a judgement call whether you should take advantage of a possible landing site along the way because the off-field landing may damage the aircraft and perhaps injure the occupants. But that must be weighed against the chance of further power loss producing a more hazardous situation; it is usually considered best to put the aircraft down at the first reasonable site. If there is insufficient power to maintain height, then of course you must set up an off-field landing. Intermittent power If the engine is producing intermittent power, and you can't determine the cause using your Plan B trouble-shooting schedule, it is probably best to use that intermittent availability to get to a position where a glide approach can be made to a reasonable off-field site. Intermittent power negates the ability to conduct a controlled approach and could get you into a dangerous situation. So having achieved a position where you can start a final approach, then secure the engine by shutting down the fuel, ignition and electrical systems. Securing the engine early means it will be colder at touchdown, reducing fire risk, but it mainly gets that job out of the way so you can concentrate on flying. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

Forced landings in recreational aircraft — due to engine/propeller failure or fuel starvation, exhaustion or contamination — are certainly not uncommon; but our pilots cope well and, in terms of injury, recreational aviation forced landings are generally uneventful. But occasionally something goes wrong. Light aircraft accident statistics from the US indicate that the most prevalent cause of a forced landing gone wrong is because the approach is too fast, leading to a heavy impact perhaps followed by a bounce and capsize. Could this happen to you? While flying at 3000 feet near Rochester, Vic in the company of two other aircraft, the pilot of the Corby Starlet reported that his engine had stopped. The landing area selected was a flat irrigation bay 40 metres wide extending 575 metres north-south and covered with short [50 mm] grass on a firm base. There was an east-west fence line across the bay approximately 175 metres in from the north boundary leaving 400 metres unrestricted for the landing. It would have been difficult to see this fence from a distance, however the aircraft had not made contact with it. Landing was from the north on a heading of 180 degrees. At about 410 metres from the northern boundary of the bay or 235 metres into the available landing area (165 metres remaining) were the start of the fresh wheel markings on the ground. They continued south for about 48 metres. It appeared that the plane may have then lifted off the ground for a short distance and then touched again. The wheel marks then continued for about 54 metres to an impact point where the plane hit a mound beside an irrigation drain. It was flung into the air, striking a fence and landing inverted on an internal farm road. The witnesses to the fatal accident, including two people on the ground, described the final approach of the aircraft's emergency landing, as "looking too fast" and again, the aircraft "flying and descending to about half a metre above the ground and maintaining that height above the ground". The touch down was made two thirds of the way along the available field . "His speed did not seem to drop in the length of the field." Ground level wind was reported to be nil. 6.4.1 Kinetic energy The safe outcome of a forced landing depends greatly on controlling the landing, which then depends on an approach that minimises the vertical velocity and the forward (ground) velocity at the selected touch-down position. This is followed by a ground run that dissipates all kinetic energy and minimises the risk of the aircraft hitting something large and unyielding. Note: the kinetic energy of a body is due to its spatial motion and equals ½ mass × speed squared ( ½Mv² — I have used the uppercase M as the symbol for mass to distinguish it from the metre). In aviation when we discuss energy management the aircraft speed (in the equation KE=½Mv²) is that which is relative to the air; i.e. the true airspeed. For the purpose of measuring the work that has to be done to bring the aircraft to a halt on the ground — which equals the kinetic energy relative to the ground — the speed is not airspeed but the velocity that is the resultant of groundspeed and rate of descent. So, touching down into wind will make a big difference to the kinetic energy level of the horizontal component of the aircraft's velocity. In nil wind conditions the kinetic energy of a 270 kg gross weight aircraft touching down at a speed of 30 knots (15 m/s) is ½ × 270 × 15 × 15 = 30 000 newton-metres [N-m or joules]. Whereas that of a 540 kg gross weight aircraft touching down at 45 knots (22.5 m/s) is 137 000 N-m, nearly five times greater. This underlines the fairly obvious expectation that very light aircraft landing at slow speeds have very much less kinetic energy to be dissipated. Correct touchdown is the most important survival skill in a forced landing and the touchdown velocity is a critical factor. For example, if the 270 kg aircraft's ground speed was reduced by 7 knots (25% reduction) to 11.5 m/s, because of landing into wind, then the kinetic energy would be reduced by 40% to 18 000 N-m. On the other hand if that aircraft was landed downwind then ground speed would be 37 knots (18.5 m/s) and the kinetic energy to be subsequently dissipated would be 46 000 N-m — 2.5 times greater than landing into wind. The landing ground roll, on a smooth unobstructed surface, would also be about 2.5 times greater. So, there is a very significant advantage in landing into wind but perhaps other conditions, such as the clear landing distance available, may negate this. Light aircraft accident statistics in the US indicate that the most prevalent cause of a forced landing gone wrong is because the approach is too fast and too high, leading to a hard touchdown followed by a bounce and capsize. This is probably because of a tendency to add a 'safety' margin (5–10 knots) to the optimum glide speed. The second most common factor is the natural tendency, when faced with some unexpectedly hostile terrain or the inability to clear an obstacle, to 'stretch' the glide distance by raising the nose — this may then lead to an uncontrolled impact in a most unfavourable attitude. Similarly when faced with an obstacle such as a powerline many pilots choose to pull up over it rather than taking a possibly safer path under it. Keep in the forefront of your mind, a controlled collision with an object is far preferable to an uncontrolled stall 50 feet above the surface — the latter generally results in total destruction. 6.4.2 Minimising impact energy in a forced landing The problem with always using the best glide speed for distance Following power loss the importance of establishing the aircraft at the best glide speed for distance [Vbg], appearing in the aircraft flight manual or pilot's operating handbook [POH], is emphasised in training and in the text books. This emphasis is valid to the extent it provides a reasonably safe initial flight speed to attain and hold whilst ascertaining the situation, planning appropriate actions and subsequent manoeuvring into the final approach position. In simulated engine failure procedures Vbg is often used throughout the approach simply because it is safer to do so; but it may not be best practice for the real thing. See 'V-speeds' for an explanation of the various codes. Note: the Vbg stated in the POH is for MTOW and should be decreased by half the percentage reduction in aircraft weight from MTOW — and of course the Vs1 and Vso stall speeds decrease in the same way. For example when there is no passenger in a two-place aircraft gross weight might be 16% below MTOW thus Vs1/Vso and Vbg (and Vmp below) are all reduced by 8%. So if the POH states Vs1 is 40 knots and Vbg is 60 knots but actual operating weight is 16% below MTOW then adjusted Vs1 and Vbg are 37 knots and 55 knots respectively. There is often an impression that in an emergency the pilot should peg Vbg and stay with it otherwise the consequences may be dire. (This concept possibly pre-supposes that a reasonable landing site is always at extreme range and that Vbg is a fixed value.) What may not be mentioned is though Vbg provides the lowest glide angle (the flattest path and hence the longest air distance), it provides neither the lowest forward speed nor the lowest rate of sink i.e. the lowest kinetic energy. (The term 'rate of sink' is synonymous with 'negative rate of climb'.) Airspeeds lower than Vbg should generally be used when in the final approach stages in a real forced landing. Vmp — the speed for minimum rate of sink When close to a possible landing site, Vmp — the minimum power (i.e. drag × speed) or minimum rate of sink airspeed — is the speed that will provide the greatest time to survey possibilities. It is also the speed providing minimum kinetic (i.e. impact) energy conditions. The airspeed/sink rate polar curve diagram at the left is a generalised plot of the relationship between rate of sink and airspeed when gliding an erect light aircraft in still air with the propeller stationary (a windmilling propeller increases drag); it is essentially an inverted power curve. Stall point is shown at Vs1. Vmp is at the highest point of the curve. The best distance glide speed is ascertained by drawing the red line from the zero coordinate origin tangential to the curve (i.e. just touching); the point of contact is where the ratio of rate of sink to airspeed is at a minimum and Vbg is directly above that contact point. Also the angle between the red line and the horizontal is allied to the angle of descent and it is obvious that Vbg occurs at the smallest possible descent angle, though it can be seen that even in nil wind conditions Vbg is not a clearly defined point value; rather, it's the mid-point of a speed range for maximum glide distance. It is apparent from the curve that any glide speed between Vmp and Vbg will provide a lower forward speed than Vbg, together with a slight reduction in rate of sink. Of course the glide path will be steeper, thus distance achieved from any particular height will be less than that achievable at Vbg. For example with Vbg of 60 knots (30 m/s) and a sink rate of 3 m/s an aircraft at a height of 60 metres would remain airborne for 20 seconds and travel forward 600 metres in nil wind. At Vmp of 50 knots (25 m/s) and a sink rate of 2.75 m/s the same aircraft would remain airborne for 22 seconds and travel forward 550 metres. (To convert feet per minute to metres per second divide by 200.) At speeds greater than Vmp there is the possibility of converting glide momentum into height maintenance for a period. However, at Vmp or lower, there is no possibility of converting glide momentum into short-period maintenance of height; any control change will result in an increased sink rate. In the diagram the Vmp is shown at around 1.2 times Vs1 and Vbg around 1.4 Vs1. The angle of attack at Vbg may be around 4–5° and perhaps 7–8° at Vmp. The increasing aoa at the sub-Vbg speeds reduces the safety margin between flight speed and stall speed so, at low altitudes, airspeed should only be reduced to Vmp in a stabilised approach after all significant manoeuvring is complete and surface obstructions are apparent. Descent at Vmp in poor visibility lessens impact a little if surface or obstruction contact is inadvertently made before flaring. In turbulent conditions the pilot must balance the possible safety of a higher airspeed against the higher impact forces brought about by that extra speed. We discuss the effects of low-level turbulence and wake vortices in 'Wind shear and turbulence'. Also pilots, particularly of low-momentum recreational light aircraft, should be aware that if a wing tip is first to make contact at low forward speed there is a possibility of cartwheeling. The penetration speed Much is said about the importance of maintaining the 'best gliding speed' during the descent but what is important is to maintain an optimum glide speed; a penetration speed that takes atmospheric conditions into account; for example, sinking air or a headwind. The gliding community refers to this as the speed to fly so that the ratio of rate of sink to ground speed is at a minimum. The normal recommendation for countering a headwind is to add one third to one half of the estimated wind speed to Vbg, which increases the rate of sink but also increases the ground speed so the ratio will again approach the minimum. For a tailwind, deduct one third to one half the estimated wind speed from Vbg, which will reduce both the rate of sink and the groundspeed, and of course there is a limit to any airspeed reduction. Bear in mind that, for safety, it is better to err towards higher rather than lower airspeeds. To illustrate the speed to fly, the polar curve on the left indicates the optimum glide speed when adjusted for headwind, tailwind or sinking air. For a tailwind the starting point on the horizontal scale has been moved a distance to the left corresponding to the tailwind velocity. Consequently the green tangential line contacts the curve at an optimal glide speed that is lower than Vbg with a slightly lower rate of sink. This is the opposite for a headwind — shown by the purple line. For sinking air the starting point on the vertical scale has been moved up a distance corresponding to the vertical velocity of the air. Consequently the pink tangential line contacts the curve at a glide speed higher than Vbg. 6.4.3 Kinetic energy can really hurt! Kinetic energy increases exponentially You may find pencil and paper a helpful back-up from here. The kinetic energy [KE] of a body is due to its motion and equals ½ mass × speed squared [½Mv²], thus as speed changes linearly KE changes exponentially. For example a 540 kg aircraft with a stall speed of 42 knots CAS might have a Vmp around 50 knots CAS, so in nil wind conditions the KE when touching down at 50 knots (about 25 m/s) is ½ × 540 × 25 × 25 = 169 000 newton-metres [N-m]. Vbg for the same aircraft might be 60 knots CAS (near enough to 30 m/s) and touchdown KE at that speed would be ½ × 540 × 30 × 30 = 243 000 N-m; a 44% increase in energy at touchdown because of a 20% increase in speed. The distance required to bring the aircraft to a safe stop is directly proportional to the touchdown energy, as is the impact energy, if the aircraft and occupants come to a premature halt. The pilot of a low-momentum recreational light aircraft is exposed to much less KE. For example consider a 270 kg aircraft with a stall speed of 28 knots, Vmp 34 knots (17 m/s) and Vbg 40 knots (20 m/s). At Vmp touchdown KE = ½ × 270 × 17 × 17 = 39 000 N-m, while at Vbg touchdown KE = ½ × 270 × 20 × 20 = 54 000 N-m. The aircraft weight is half that of the heavier aircraft but impact KE is one-fifth. Kinetic energy is substantially affected by wind velocity Usually when we discuss in-flight energy management the aircraft speed (in the equation KE=½Mv²) is that which is relative to the air — the true airspeed. However, for the purpose of measuring impact energy or the work that has to be done — i.e. the energy expended — to bring the aircraft and occupants to a stop, the speed is not true airspeed but the velocity resultant of ground speed and rate of sink; thus touching down into wind with a low sink rate will make a very favourable difference to energy level. If the 270 kg aircraft's Vmp ground speed is reduced by 6 knots (18% reduction) to 28 knots (14 m/s) by landing into a 6-knot wind then KE is reduced 33% to 26 500 N-m. In the same conditions if that aircraft was landed downwind then ground speed would be 40 knots or 20 m/s, and the KE to be subsequently dissipated would be 54 000 N-m — the possible impact would be twice as great as landing into wind — and 6 knots is just a pleasant light breeze. The figures for the 540 kg aircraft landing at Vmp with a 6-knot headwind and tailwind are 131 000 N-m and 212 000 N-m respectively; quite a difference from the nil wind impact of 169 000 N-m even with just that light breeze. (It also underlines the fairly obvious expectation that low-momentum recreational light aircraft landing into wind at minimum speeds don't have a lot of energy.) There is a very significant advantage in a low-speed into-wind forced landing, but other conditions — such as clear landing distance available — may modify this. A worse case is when the aircraft touches down both fast and downwind. For example if our 540 kg aircraft touches down somewhat fast, say 65 knots CAS, with a 6-knot tailwind then the KE at touchdown is ½ × 540 × 35.5 ×35.5 = 340 000 N-m; twice the energy at 50 knots in nil wind conditions. It also reinforces the point that, with the ever-present possibility of engine stoppage or degraded performance, it's a silly decision to take off downwind, no matter how long the distance available — unless it's a one-way downhill strip. But let's look at the case where only the pilot is on board, our aircraft weight is 16% below MTOW at 454 kg, and the pilot lands at a Vmp reduced by 8% to 46 knots into a 6-knot headwind. Then the KE at touchdown is ½ × 454 × 20 ×20 = 91 000 N-m, a very significant decrease from the previous 340 000 N-m. High density altitude adds kinetic energy Density altitude also affects KE because TAS is about 1.5% higher than CAS for each 1000 feet of density altitude. For example the density altitude at Armidale, New South Wales (elevation 3500 feet) with temperature of 30 °C would be around 6000 feet, which means that the TAS will be about 9% greater than CAS. So using the preceding example of 540 kg touching down at 65 knots CAS, the TAS at 6000 feet density altitude would be 71 knots. So adding the 6-knot tailwind for a touchdown groundspeed of 77 knots the KE is then ½ × 540 × 38.5 ×38.5 = 400 000 N-m. The density altitude adds 60 000 N-m; quite a lot of energy that you need to be aware of. Always bear in mind that Australian climatic conditions are significantly warmer than the latitude 40°– 45° N climate on which the International Standard Atmosphere (and consequently airspeed indicator dial calibration) is based. In summer day temperatures the airfield density altitude would be from 2000 feet to 3500 feet greater than the airfield elevation. See The Civil Aviation Safety Authority declared density altitude charts. You must expect that TAS is significantly greater than IAS. Doing the KE calculations for the aircraft you fly Kinetic energy calculation is easy if you first halve airspeeds and windspeeds to convert from knots to metres per second and express the operating weight (mass really) in kilograms; i.e. KE= ½ operating weight × groundspeed squared — the result is in newton-metres or joules if you prefer. 6.4.4 Plan and control the potential crash! Be well prepared There is some element of chance in every emergency landing (Murphy's Law suggests that what can go wrong will go wrong, and at the worst possible time), but being well prepared and keeping cool (but not so cool that you freeze up) are by far the most important factors in deciding the outcome. A safe outcome greatly depends on placing occupant safety before airframe loss, knowing your aircraft, and on fully controlling the approach and landing/crash. The latter depends, firstly, on carefully flying an approach (having selected the best readily attainable landing site) that finally minimises the forward speed and the sink rate at a nose up/wings level touchdown; thus minimising impact angles and better distributing the initial impact forces. It is best to dissipate excess energy as drag while still in the approach by using full flaps or side-slipping; both together if acceptable, though some aircraft are downright dangerous if side-slipped with full flap. Secondly, plan the direction of the subsequent ground travel so the remaining energy is substantially dissipated before the occupant enclosure hits something large and unyielding, or a barbed wire cattle fence, or the aircraft overturns. In short; you must plan and totally control the flight all the way into the potential crash. So what final approach speed should be chosen? Comment from CAR 35 engineer Dafydd Llewellyn: "It is often difficult to hold a steady speed on short final, even if there is no wind shear; it is not commonly appreciated that most aeroplanes have considerably degraded longitudinal stability in the landing configuration. Firstly, they have a greatly increased pitching moment coefficient due to flaps etc and secondly, they are close to or below the minimum drag speed — and both of these effects tend to make them speed-unstable. This is reflected in FAR 23.175, which requires a positive stick-force gradient in the landing configuration, with power off or only with sufficient power to maintain a 3 degree angle of descent. Try it with more power that this, and you will often find — especially if the cg is somewhat aft — that the thing cannot be trimmed to any given speed; it's actually negatively stable (this is the reason such care is needed in a baulked landing). If disturbed in speed, by turbulence for example, it will continue to slow down or speed up. The stick force versus speed gradient may be positive below this power, but it's usually pretty small, so the thing is a lot less stable than in cruise. This is why it's so critical to keep an eye on the ASI, in those phases of flight, and almost certainly the root cause of the high proportion of accidents that occur in the landing and aborted landing phases. Most pilots are not aware of this." After considering the trade-off between adequate controllability, margin from stall, and excess kinetic energy the optimum speed over the fence is probably 1.3 times Vso (the stalling speed in the landing configuration at the particular operating weight); it will be 3– 4 knots faster than the corresponding Vmp. Add no more than 5 knots in gusty conditions and resist any compulsion to add any additional 'safety' margin. Make sure Vso and the approach speed are both determined in terms of CAS rather than IAS, as the ASI may have significant, but not comparable, position error corrections at Vso and 1.3 × Vso. Flare with care! In the final approach, the aircraft aoa may be somewhere between 5° and 8°, and the flare to arrest the rate of descent may raise aoa close to critical, and the increased drag will slow the aircraft quickly — thus a rapid increase in rate of sink will follow. It is usually essential that the aircraft is flared gently, smoothly and at the height appropriate for a consequent near-stalled or fully stalled touchdown — but see 'Alighting in tree tops'. In some aircraft the loss in slipstream (compared with that from an idling engine in a normal landing) may significantly reduce the elevator authority and thus the stick must be pulled back further to flare successfully. If possible, correct crosswind drift before touchdown so that side-impact forces are reduced. (The term 'dead-stick landing' — an 'in-word' used to describe a forced landing following complete loss of power (or a training exercise where the engine is shutdown on approach) — originated during World War I. It is thought to describe the decreased elevator authority following loss of the slipstream in some of those early aircraft. Nowadays the use of the term is deprecated — no one describes a normal sailplane landing as 'dead-stick'.) The possibilities of landing safely downslope may range from difficult to impossible. A strong headwind may make a downslope landing feasible though it is difficult to judge the degree of slope until you are close to the surface and thus committed. Moderate upslope is good if the pre-touchdown flare is well judged. There is a much greater change in the flight path during the flare; for example if the upslope has a one-in-six gradient (about 10°) and the aircraft's glide slope is 6° then the flight path has to be altered by 16° so that the aircraft is flying parallel to the upslope surface before final impact. A higher approach speed is needed because the increased wing loading during the very pronounced roundout/flare (a turn in the vertical plane) increases stall speed. If the wind is upslope then a crosswind landing may be feasible. 6.4.5 Deceleration forces and energy absorption Load factors The KE of a 540 kg aircraft touching down at 45 knots groundspeed is 137 000 N-m. If, in a normal landing on a prepared airstrip, the aircraft is uniformly decelerated to stop 100 metres from touchdown then the deceleration force — the total forces applied to stop the aircraft — is KE/distance (N-m/m) = 137 000/100 = 1370 newtons. The deceleration forces place a load on the aircraft and the airframe transfers a load to its occupants. It is usual to compare such load factors in terms of the non-dimensional 'g ratio' calculated, in this case, by dividing the uniform deceleration force by the aircraft's weight in newtons (its mass in kg multiplied by the acceleration of gravity — close to 10 metres per second per second) which, in the example, would be 540 × 10 = 5400 N. Thus the horizontal deceleration factor is 1370/5400 = 0.25g — just a slight load which probably wouldn't register with the occupants; it can also be seen that the aircraft is decelerating at the rate of 2.5 m/s² (i.e. 10 × 0.25). If the family sedan is brought to a controlled stop under heavy, sustained braking the occupants would be unlikely to experience more than a 1g deceleration. If the aircraft, under uniform deceleration, came to rest in 10 metres then the deceleration force is 13 700 newtons and the load factor is 13 700/5400 = 2.5g. But if uniformly brought to a halt in 5 metres by landing in dense, light scrub then the deceleration force is 27 400 newtons and the forward deceleration load factor is 27 400/5400 = 5g. Of course the aircraft's velocity at impact includes a vertical component, but we will look at that later. It is unlikely that in the early stages of ground travel, after a planned and controlled forced landing approach, a light aircraft would slam head-on into a large unyielding object, such as a large tree trunk or a very large boulder. On the other hand, it is also unlikely that an aircraft will be uniformly decelerated — the surface conditions may be such that varying impact loads (from contact with brush, saplings, stumps, roots, stones, holes, furrows) are intermittently applied to the airframe and occupants from near touch-down until coming to a stop, making it impossible to control direction, or even keep feet on the rudder controls. These multiple impacts result in a series of peak deceleration loads applied for very short periods, probably a few hundredths of a second, and felt as severe jolts; many of these will have a sideward load component. A note of caution. A firm touchdown with no float in ground effect is the aim but if you are forced into dissipating excess airspeed by holding off half a metre above the surface and the undercarriage strikes a rock or stump then the consequences are likely to be more traumatic than if you had pegged it down earlier at the higher speed and then run on into the object. Ground-assisted deceleration is better than ground effect float. The consequences may also not be good if you are holding off and pull back on the stick to avoid tripping over an obstruction. So if the terrain is cluttered with unavoidable obstructions of that nature then it may be best to place the main wheels on the ground earlier even though the velocity, and thus kinetic energy, is higher. If the distance between relatively high obstructions is less than the wing span try to steer a course that will equally distribute the impact forces on each wing so that the cockpit enclosure is not spun around into something unyielding. Of course if landing on a clear surface the aircraft will slow faster with its wheels on the ground than if held in ground effect, but the faster the speed at touchdown the greater the possibility of bouncing. Airmanship is about making and implementing the wisest choice in such difficult situations. For example, when faced with an obstacle such as a rural powerline many pilots might choose to pull up over it rather than taking the possibly safer path under it. That natural tendency, when faced with some unexpectedly hostile surface or the inability to clear a previously unseen obstacle, to 'stretch' the glide distance by raising the nose excessively, may lead to an uncontrolled impact in a most unfavourable attitude. A controlled collision is far preferable to control loss 50 feet above the surface — the latter generally results in severe injury or worse. It is probably better to put it between obstacles that are closer together than the wingspan, than to stretch the glide and then drop-in nose first. Protect the occupant zone by sacrificing the wing structure. It is best to avoid higher-speed impact with a strong, barbed-wire fence by ground looping, if possible. The following is an extract from a detailed incident report by a Boorabee pilot who did everything right when the engine packed up: "... the positioning and timing seemed to come together almost at a crawling pace, but it must have been just a few seconds. The turn onto final had to be made at low level so I made a definite intent to ensure good speed into the turn. Turned onto the final approach high enough to clear the barbed wire fence and fast enough to have full control and touched down beyond the fence parallel with the ploughed furrows ... recall pushing the nose down just enough to ensure longest distance possible for ground roll as the dirt paddock would retard the motion a lot faster than flaring and easing onto the ground halfway up the paddock ... noisy and bumpy ride with underside of pod sliding along top of furrow ... ground looped to halt the aircraft when getting close to the end fence and into cross ploughing ..." Tailwheel aircraft have an advantage over nosewheel aircraft on rough ground. The tailwheel is likely to be pulled over obstacles but even if it is knocked off, the aircraft remains stable and is converted into a true 'taildragger' with its built-in arresting effect. On the other hand recreational light aircraft nosewheel structures are not very strong and if a nosewheel can't be held off then it tends to be pushed into holes and may not ride across or over obstacles — the consequences may be loss of the nosewheel strut and of aircraft ground stability. In the worst case the aircraft nose may dig in and the aircraft flip onto its back; in which case ensure you are in an aircraft where the design includes a structure that rests on itself rather than the occupants heads, and there is an escape route from the inverted cockpit. Some aesthetically pleasing bubble canopies with unobstructed views may be death traps; steel roll-cages/bars or high-wing aircraft are safer. The accident/incident reports indicate a surprising number of aircraft end up inverted following a forced landing or other landing mishap, but certainly for the high-wing aircraft the damage to the airframe is generally not total and injuries are low. If your heart is set on a low-wing or mid-wing aircraft first figure how you and your passenger will escape when it's inverted. Energy absorption From the foregoing it is evident that very little distance is required to bring the aircraft to a safe halt IF the kinetic energy can be dissipated uniformly during ground travel. For example the occupants of the 540 kg aircraft touching down at 45 knots and uniformly brought to a stop over 20 metres would experience about 1.25g deceleration. (In the days of heavy piston-engined aircraft conducting carrier landings the arresting load was 2–3g, which was not uncomfortable when well strapped in.) So where there is no clear, open space to land the aircraft, more or less normally, then an option is to choose an area where the vegetation is of sufficient height and density to absorb much of the kinetic energy and retard the aircraft. If that vegetation is weaker than the aircraft structure so much the better, but the primary consideration is occupant safety so energy absorption by sacrifice of non-vital aircraft structure — i.e. all that outside the occupant zone — is warranted. The requirement of course is to set up the touchdown so the aircraft is moving in a direction where the vital structure is unlikely to slam into an unyielding obstruction at speed. High and dense crops, sugar cane, brush and light scrub all provide good energy-absorbing properties and good cushioning is provided if the aircraft is put down in the proper nose-high attitude so the impact forces have more spread over the aircraft's under-surfaces, rather than just catching at the undercarriage and overturning the aircraft. But even an unfavourable impact angle may not be particularly dramatic; e.g. here is an extract from a forced landing incident report: "The Jabiru impacted the sugar cane in a 20 degree left wing low attitude and came to rest upright after sliding 20 metres." Again — the emphasis is on controlling the crash and spreading the impact loads " ... I decided to land in a cane field ... the Jabiru was held off until it stalled when full left rudder was applied to slew the aircraft sideways to prevent it from going over on its back ... the event was successful and neither of us were injured. Impact forces are less if you touchdown at Vmp or a little higher and then run on into obstructions at the far side of a clearing rather than stall/spin at the near end. The aircraft structure will withstand longitudinal impact forces much better than concentrated lateral impact forces (such as side-swiping a tree trunk), so generally avoid touchdown with substantial drift or slip towards the lower wing, unless you are in a position where the impact loads will be widely spread, as in the cane field landing above. 'Alighting' in tree tops is certainly extremely hazardous and always results in total aircraft write-off. But if the aircraft is flown into a selected, dense crown in a reasonably nose-high attitude (and into wind) — so that some of the initial impact is absorbed by the under-surfaces of the fuselage, tailplane and wings — then the hazard to occupants may be reduced. It is important that the aircraft is not stalled above the tree crowns, because of the possibility of the nose and/or wing dropping into the crown before impact; rather, it should be flown into the canopy at the minimum sink glide speed. The greatest hazard may come from a subsequent slide, of the fuselage remains, from the tree. Easier said than done, but certainly the aircraft must be flown all the way into the crash. The following is a summary of an accident report; the aircraft was a Skyfox CA22, the pilot had 16 000 hours experience and rescue was fast: 'While on cruise at 1100 feet agl the engine failed completely. The pilot set the aircraft for a forced landing into heavily timbered terrain and transmitted two mayday calls. The second call was answered and he gave details of his situation and position. He then maintained control of the aircraft until it touched the top of the tree canopy where he flared steeply, as the aircraft entered the trees, to present the underside of the aircraft for speed reduction and impact damage minimisation. The pilot suffered bruising to one knee and was transported to hospital by an RAAF helicopter. The aircraft was severely damaged.' The following is a report from a Jabiru passenger in another treetop alighting. The pilot, using a runway downslope advantage, took off toward the north with a five to eight knot south-east wind. The pilot had just turned crosswind at about 350 feet agl to avoid a noise-sensitive residential area when the engine died. There was no clear area within gliding distance — only a full expanse of mature eucalyptus trees some 20 to 40 feet high. The pilot lowered the nose to maintain 65 knot best glide speed and turned the aircraft slowly into wind for the landing. The passenger (an RA-Aus CFI along for a ride home) takes up the story. "The trees were rapidly getting closer. They changed from a mass blur to individually defined trees and I prepared myself for the worst. The pilot tried the engine again unsuccessfully, then turned fuel and magnetos off. He started making a mayday broadcast, but before the transmission was complete, there were sounds of trees and aircraft breaking bits off each other as first contact was made. Full marks to my pilot as he unerringly and unhesitatingly flew us right into the tree canopy, our only survival option. This went by the book. The pilot flew us onto a selected tree top, raised the nose a little to slow down our forward airspeed and then expertly used the top of the tree to slow us down still further from an estimated 60 to 40 knots, yet left us with sufficient forward speed to prevent the deadly vertical fall to the awaiting ground immediately below. Seemingly incredible deceleration forces tried to rip me out of my seat — thank goodness for seat belts. We hit a sapling trunk with the inboard section of the starboard wing and decelerated rapidly as we were flung violently to the right. The engine cowling disappeared, exposing the engine which ripped outwards right in front of my field of view, dragging the firewall and windscreen area with it. Next I was aware that we were bouncing backwards, then falling vertically some 10 to 15 feet. We hit the ground with an almighty thud. I became aware of smoke and electrical zapping noises coming from the distorted centre console/instrument panel, which lay on its back with the gauges pointed to the sky. "Get out! Get out!" I yelled to the pilot, who was still sitting in the left hand seat looking a little stunned. I couldn't exit my right-hand side door as something was jamming it. I was keen to get out as quickly as possible as sparks, smoke and arcing were coming from the damaged central instrument console and we had at least 30 litres of fuel sitting in the cockpit right behind us. I followed the pilot out his side door and touched the ground with relief. However, I discovered I was in immense pain, which worsened when I tried to stand up. Due to my fear about being in an 'aircraft inferno' I left the immediate scene of the accident and headed towards the nearest road. I yelled to the pilot to follow me and hobbled off." Deceleration effect of sink rate In a forced landing there is normally no power available to vary the rate of descent or arrest sink, and often high sink rates are not recognised early enough, but it is extremely important that the downward component of the aircraft's velocity at touchdown be minimised. So in the last stages of the approach, after all manoeuvring is completed, the airspeed should be close to Vmp. A high sink rate at touch-down can result in an uncontrolled crash rather than a controlled landing. If the descent rate of our 540 kg aircraft was 300 fpm (1.5 m/s) and this was not arrested in the flare before touch-down, then the kinetic energy of the vertical component of the aircraft's velocity would be 7% (1.5/22.5) of 137 000 = 10 000 N-m. If the undercarriage (which held the aircraft 0.5 m above the ground) collapsed and the downward movement was arrested in 0.5 m then the downward deceleration force is 20 000 newtons and the downward load factor is 20 000/5400 = 3.7 g. Here is a witness comment in an RA-Aus double fatality report: "The take-off on the 1200 metre runway was sluggish and the engine was misfiring. (Fuel was later found to contain a substantial amount of diesel!) The Murphy Rebel continued climbing and turned toward the east then right again onto a low downwind leg. In the mid-downwind position a loud bang was heard and the aircraft then descended flatly ... it appeared that the aircraft had a slow forward velocity but a high rate of descent when it struck ... came to rest 16 metres from the initial impact ... cockpit area and engine bay badly damaged by fire ... the reason for the inadequate airspeed in the forced landing may have been false horizon effect as the aircraft was approaching rising ground." What is most concerning, from a perusal of the accident/incident reports, are the occasions where a forced landing precursor has been the engine displaying ample warning of a problem before take-off or while in the circuit area (as described above) but the pilot seems to have been hoping that it would fix itself and opted to press on — why? What could possibly be gained? Aircraft design regulations The Federal Aviation Regulations Part 23 lays down some crashworthiness requirements for normal category light aeroplanes to give each occupant every reasonable chance of escaping serious injury when the occupant experiences forward loads up to 9g and sideward loads up to 1.5g. So, in theory, if a certificated aircraft touches down under control and decelerates at a constant 9g forward, the occupants should escape serious injury — provided the lapbelts and shoulder harnesses are properly used and cockpit intrusions are avoided. FAR Part 23 also has a 6g downward load requirement. What this means is that it is possible that a normal category aircraft, touching down at 45 knots, running into something sufficiently yielding (for example scrub and small saplings) and decelerating at 9g will come to a halt over a distance of just 3 metres (during a time of one second) with the occupants only suffering body bruising from properly fitting harnesses and perhaps some minor injuries to the legs and arms; provided the occupant zone remains reasonably intact and nothing intrudes into it. Of course, the rest of the aircraft itself will not come out of it so well. Many of the top-end recreational light aircraft fit into that FAR Part 23 'normal' category. By the way, rocket-deployed aircraft emergency parachute recovery systems generally aim for a maximum descent rate of six metres per second (1200 fpm). Minimum ultralights and powered parachutes At the very light-weight, low-speed (55 knots maximum level flight speed) end of the ultralight aircraft spectrum are the homebuilt single-seat minimum aircraft, the airframes of which are often constructed from aluminium tubing and sailcloth. The design, the structural integrity and the impact resistance of such aircraft will certainly not provide the 9g occupant protection required of the type-certificated aircraft but their kinetic energy, when touching down into wind, is very low — in the range 10 000 to 18 000 N-m. In a controlled landing, if such an aircraft was uniformly decelerated to a stop over 5 metres the force would be less than 1.5g. Powered parachutes are in the low end of this minimum category. 6.4.6 Your final defence perimeter — a safe occupant zone Momentum and occupant safety The airframe density per cubic metre of finished structure is generally homogenous but the engine, fuel and occupant bodies have higher densities — thus a higher momentum (momentum = M × v) than the rest of the aircraft — and should all be properly restrained. The engine by very strong mountings, particularly if mounted behind the occupants; and the occupants by an adequate seat/restraint system so that the core fuselage structure, engine and occupants all decelerate at the same rate even though a considerable part of the aircraft may be sacrificed along the way. Re-read the preceding description of alighting into tree tops. There should be no loose objects in the aircraft — they will become a harmful missile. If the adult body is properly restrained, human organs and their attached blood vessels, will cope with transverse deceleration loads very much greater than 20g — applied for short periods. However the spinal column has a much lower tolerance to downward deceleration loads; i.e. loads applied parallel to the spinal column. In this aspect the skeletal structure is much weaker than the aircraft under-structure and downward deceleration loads may result in serious spinal injury — thus the importance of minimising the vertical velocity at impact. Occupant restraint system The pelvis-hip girdle is the strongest part of the body structure and the body's centre of gravity lies between the hip bones. The better occupant restraint systems usually consist of a seat and seat-back, a firm seat cushion, a lapbelt angled to hold the hips into the internal corner of the seat and a shoulder harness system to prevent forward/sideways movement of the upper torso. Shoulder harness systems are usually an adjustable webbing strap over each shoulder that clip to the lapbelt; the shoulder harness may incorporate an inertia reel system. A lap and sash belt, as used in the family sedan, is effective and might be used in a minimum aircraft. The following should be noted: The occupant restraint system must be designed for the occupant(s) and the conditions likely to be experienced in that aircraft. The airframe or seat attachment positions and angles for the harness system must be such that the adjusted lapbelt will remain across the occupant's hips and the shoulder straps on the shoulders during impact. The diagram is an example of the harness geometry guidance material from BCAR S. If the seat should collapse or the seat back fails during impact, there is a possibility that the occupant's body may then slip forward beneath the lapbelt. The same problem — submarining — can occur if the lapbelt hasn't been tightened sufficiently or if a badly designed seat slopes downward from back to front. If submarining occurs and the forward slide is sufficient that the lapbelt is repositioned above the pelvic girdle, then consequent impact loads (and the rotation of the body about the lapbelt) can cause abdominal and spinal injuries. Extended submarining has resulted in strangulation by the harness. These problems are readily overcome by incorporating a fifth strap (the crotch strap) into the harness, locking the lapbelt in position against the pull of the shoulder straps and preventing bodily slip. When fastening the harness, first position the body correctly in the seat then follow the correct fastening and tightening sequences — lapbelt across the hips not the abdomen, pulled very tight (then the crotch strap if fitted), and then the shoulder harness reasonably tight but without displacing the lapbelt position. Don't totally release the shoulder harness straps in flight to facilitate easier movement; you may neglect to re-attach them properly in an emergency. Perhaps the best value safety harness type for a very light 3-axis aeroplane is a Confederation of Austalian Motor Sport approved 5-strap automotive racing harness, which costs less than an "approved" aircraft harness, and probably offers better protection, but any harness is only as good as its anchor points and their position relative to the occupant and their surrounding airframe structure. In a sudden deceleration, momentum carries the upper body forward, stretching the shoulder harness, then stops and the upper body and head whip back. A wide, deep headrest will provide some whiplash injury protection, but a large number of aircraft seats lack headrest protection. During pre-flight inspection check the webbing, inertia reel and fastener condition and integrity and the seat mounting integrity. If the seat is the moveable type check the rail holes or slots; if they are deformed the seat may slide back on take-off or may twist and detach under impact forces. When initially settling in to the seat make sure that you can comfortably — i.e. without straightening your leg — apply full left and right rudder. If you cannot adjust the seat or rudder bar to achieve this, do not fly that aeroplane because you will not have the full rudder authority judged to be needed and provided by the designer. Also there is a high probability that, with the knee joint locked while applying full rudder — to steer the vehicle on the ground or initiate a ground loop — any impact forces transmitted via the rudder bar may severely damage the hip socket. You must be able to apply full rudder with the knee still bent. If the aircraft is fitted with adjustable seats make doubly sure that the seats are locked and in a comfortable position before starting the engine. Do not attempt to relocate the seat position during an emergency landing. Great care must be taken with child restraint systems Infants cannot be carried in ultralight aeroplanes and it is most unwise to carry small children (say under 15 kg) as a passenger; there is no satisfactory restraint system. They cannot extricate themselves and they cannot go for help. Children weighing between 15 and 25 kg should use a government-approved child restraint system [CRS]. The US approved types have 'This restraint is certified for use in motor vehicles and aircraft' printed on them. The CASA advisory publication CAAP 235-2(1) contains more information on CRS standards. Children over 25 kg and 145 cm tall might be restrained safely within a normal fully adjustable four-strap (preferably five-strap) seat harness. A booster cushion might be used if they don't quite make the height. Safest approach is to never carry children who are not old and strong enough to extricate themselves safely (and unaided) from the harness and a wrecked cockpit. Personal protection equipment Perusal of the accident/incident reports for 3-axis aeroplanes shows that rather few pilots or passengers were wearing head and face protection at the time and no doubt some are now wondering why they chose not to wear personal protection. Using the correct type of helmet and inner energy-absorbing pads will provide considerable protection from serious head injury if the occupant zone be deformed, intrusions occur or the restraint system fails. Helmets also reduce the chances of being knocked unconscious in a wreck that subsequently catches fire. There are quite a few high quality sport aviation helmets available, though they are not cheap. Two helmets with face vizors and an intercommunication facility may cost $1500 to $2000. Children must always wear an appropriate helmet and liner. Why do parents who won't allow their child to ride a bicycle in the backyard without a helmet take them flying with no such protection? Crush zones In theory the distance over which the aircraft is brought to a stop is the distance over which the aircraft's centre of gravity travels. Thus provision of an energy absorbing crush zone or deformable structure in the front of the occupant zone, even if it just adds half a metre to the distance, adds to the occupant stopping distance and reduces the deceleration forces on the occupants. Generally the structure of the under fuselage does not incorporate a crush zone to provide some occupant protection from spinal injury, so it is advisable that aircraft with a retractable undercarriage should be landed with the gear down. That will absorb quite a lot of vertical load before collapsing. Some aircraft seats may be designed as a deforming, load-absorbing system in which case it is important that nothing is stowed beneath the seat. In a low-wing aircraft the pilot/passenger seats are probably directly over the main spar — which is obviously built not to collapse — so, if there is no crushable structure between the seats and the spar, the occupants' spinal columns will be directly exposed to the full vertical deceleration. In that case ensure the seat includes something similar to a body-conforming, energy-absorbing, 3-inch thick seat cushion laminated from three layers of Confor urethane foams or similar. Nearly all light aircraft have a fixed undercarriage; there may be a problem with some low-wing aircraft fitted with in-wing fuel tanks if the collapse of the undercarriage causes penetration of those tanks. In a fixed, high-wing aircraft (excluding minimum aircraft) the overhead structure provides a crush zone sufficient to allow exit room from the cockpit if the aircraft pitch-poles onto its back. Also the cockpit is fitted with doors that can generally be forced open when the fuselage is inverted; even when rolled-up into a ball, as seen in this Cessna Skyhawk image. In some low-wing, bubble cockpit canopy aircraft the cockpit area may be the weakest part of the fuselage structure. If such aircraft are involved in a forced landing where the aircraft nose digs in, the occupant zone may distort sufficiently to allow failure of the occupant restraint system; also there have been cases where, during a rapid deceleration, the outward buckling at the cockpit allows the momentum of the rear fuselage to swing itself over the cockpit enclosure. There may be insufficient roll-bar or other structure — except possibly the vertical stabiliser — to prevent crushing of the cockpit canopy in a capsize. Even when a strong roll-bar bow is incorporated, if capsize occurs, unaided exit of the pilot/passenger may be near impossible until the aircraft is lifted. If the aircraft is fitted with a canopy that can be jettisoned in flight, make sure the front canopy bow cannot drop down during the jettison process and scalp the occupants. All occupants should wear safety helmets in aircraft with bubble-type canopies and consider stowing a suitable pry bar/escape axe/fireman's axe in the cockpit. Structure integrity and impact resistance From the foregoing it is evident that aircraft with very low kinetic energy near stall speed require a lesser degree of occupant protection from impact forces and intrusions into the occupant zone — apart from the restraint system. As the kinetic energy at the aircraft stall speed increases, then the aircraft structural integrity and impact resistance must be engineered to provide increasingly higher standards of protection. 6.4.7 Aircraft emergency recovery parachutes Some factory-produced aircraft are now fitted with rocket-deployed aircraft parachute recovery systems as standard equipment. Builders/owners of homebuilt aircraft often choose to add systems which could be spring deployed, mortar deployed or rocket deployed. The parachute recovery systems are primarily intended for use following events such as mid-air collision, catastrophic structural failure, pilot incapacitation, engine failure over difficult terrain or water, unrecoverable or low-level spin, and disorientation/loss of control in IMC. They are generally very effective in such situations. In the case of inflight fire parachute deployment should be delayed as long as possible in order to limit the hang time. The parachute systems are not intended for use in a normal forced landing event except possibly as a braking 'chute in a tight squeeze (see below). The parachute canopies are circular with a central vent (quite unlike a parachute wing), have a diameter around 12 metres for a 544 kg aircraft or 10 metres for a trike, and the length of the harness and lines from the aircraft to the canopy rim would be around 15–20 metres. So, the aircraft may be oscillating on quite a long arm. This oscillation will be greatly increased in gusty conditions as the canopy has a lot less inertia than the aircraft — as powered parachute pilots will be aware. On deployment of the parachute the aircraft may initially experience a deceleration around 3—5g depending on the aircraft's speed, so it is advisable that four-point occupant harness systems are fitted. From activation, it will take perhaps two or three seconds for the parachute to fully open then another four or five seconds for the aircraft to stabilise in the appropriate attitude (wings level and perhaps slightly tail-down to provide additional energy absorption). The aircraft would descend at a target maximum rate around 6 metres per second (1200 feet per minute), at which vertical velocity the aircraft will impact the surface. The undercarriage system is probably designed to absorb energy equivalent to around 3g. The balance of the kinetic energy would have to be absorbed by collapse of the undercarriage and other structural crushing. The horizontal velocity at impact will be the wind velocity near ground level. Depending on aircraft weight, speed and parachute type the loss of height from activation to stabilised descent is likely to be 100–300 feet if deployed when the aircraft is in a reasonably level attitude, so deployment is best activated above that height. However, in emergency conditions the aircraft is not usually in a reasonably level attitude, quite the reverse — it may be steeply banked and nose pitched down, even inverted, so the safe height may be much greater than 300 feet. For tractor-engined aircraft the rocket deployed recovery system is usually installed in the fuselage with the rocket's ascent path slanted at a rearward angle to the aircraft's longitudinal axis. But for a trike, it may be deployed sideways or at 45° to the longitudinal plane; so, there is much to be considered when estimating safe height for deployment. If the aircraft is not established in the appropriate attitude, with the minimum vertical velocity at impact, it is likely that damage will be severe, a combination of the wind velocity and, for example, a nose-down attitude could capsize the aircraft and perhaps drag it a short distance. In an emergency situation below a minimum height the only feasible action may be to activate the recovery system. It would not be the usual practice to deploy a recovery parachute in a normal forced landing, but in a limited space it might be used successfully as a braking parachute if deployed just after touchdown when the aircraft's momentum is low. (When a parachute is deployed above the aircraft it acts as an 'air anchor' and the aircraft's momentum will tend to swing the aircraft upwards which, when near the surface, may then follow with a tail-slide into the ground.) After use the complete system must be returned to the manufacturer's agent for restoration; substantial cost will be involved. Safety pins should be disengaged before take-off and re-engaged after landing; in a low-level in-flight emergency there will be no time available to fiddle with safety pins. The rocket propellant is quite stable; however, it is possible that the ignition system can be activated accidently if the airframe is distorted in a forced landing or a ground accident. An armed rocket is a serious safety risk to anyone attending the site of an accident, so hazard identification and warnings must be provided on the external surfaces of the aircraft. Passengers must be fully informed on both the operation of the system — should the pilot suffer inflight incapacitation — and the dangers of inadvertment activation. Read the CASA bulletin AWB 25-003 'Inadvertent Activation of Rocket-Deployed General Aviation Recovery Device (GARD) During Maintenance'. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

6.3.1 A remarkably easy way to top yourself! How much height might be lost in a stall/spin incident? The pilot in that intended fly-by failed to recognise the stall in the turn and had no time to recover from the consequent first stage spin; he had perhaps only reached 300 feet agl when everything turned sour. The height lost during a normal stall and recovery incident in a very light aircraft is probably between 50 and 250 feet; depending on atmospheric turbulence, the aircraft type, the aircraft attitude at stall, the docility of stall onset and the pilot's awareness of the incipient (beginning or initial stage) stall. However, loss of height in a stall/spin event, as described above, is very much greater, perhaps 100–300 feet during the incipient spin stage, 200–400 feet to stop the autorotation and 300–500 feet during the recovery; a total of 600–1200 feet if the incipient spin is allowed to develop into autorotation. Do YOU make sure you know the accelerated stall characteristics of the aircraft you are flying? Unfortunately many pilots are not wary of the stall onset when the wings are loaded up, because they are used to benign stalls and have never explored an aircraft's accelerated stall characteristics; which will be different — and in some aircraft quite viciously so — to the normal 1g stall characteristics. No pilot can escape from a stall/spin event if there is insufficient height to do so, but prompt recognition of the incipient stall and fast corrective action can save the day. All of which is why low-level stall/spin events are so absolutely deadly and why the only real solution to a stall/spin event is absolute avoidance; all the spin recovery training you may undertake is not going to help once the aircraft is spinning below the minimum recovery height. Stay within the aerodynamic limits and never place the aircraft in any situation which would make such an event possible; fly the aeroplane or, more to the point, make sure the wing and tailplane always keep flying! Never, never indulge your self-supposed ability to produce fast pull-ups on take-off or a wing-over and beat-up. Developed spin recovery training is not included in the RA-Aus Pilot Certificate or the GA Private Pilot Licence syllabus, though stall and incipient spin awareness and recovery are normal parts of both syllabi. However, please read Autorotation — the fully developed spin and Spin recovery confidence building in the flight theory section. This is near to last in an award winning photo sequence of a stall/spin accident. Taken by Ian Ward, published in the 'Wimmera Mail Times' and subsequently in the AUF magazine. In this image autorotation seems to be established with the nose yawing downward and the aircraft rolling to the right. Note the pilot's totally natural ground rush aversion reaction: full back stick (evidenced by the elevator position in all photos) thus holding the aircraft in the stalled condition. Also the pilot is endeavouring to roll the aircraft upright with aileron (starboard aileron down), but consequently deepening the stall, and thus increasing the lift loss and the drag on the down-going and non-flying starboard wing. The pilot had no escape from the inevitable. Failure to recognise the aircraft condition is not confined to relatively inexperienced pilots. In June 2009, the three-pilot crew of an Airbus 330 operating as Air France flight 447 (and following an airspeed indication aberration) failed to recognise that they were holding the aircraft in a fully stalled condition with a pitch attitude of around 16° nose-up and an angle of attack above 35°, while the aircraft was sinking at 10 000 ft/min. The engines were responding normally to pilot inputs. That stalled descent continued for 3.5 minutes from 38 000 feet to the surface of the Atlantic, where all 228 persons on board perished. Similar disastrous failures, on the part of the flight deck crew, to recognise the stalled condition have occurred previously; for example, in 2005 a West Caribbean Airways MD-82 crashed in Venezuela after sinking from 36 000 feet in 3.5 minutes — 160 persons perished. Some refresher notes on the pertinent aspects of aerodynamics Before proceeding further, the following are some refresher notes on a few pertinent aspects of aerodynamics — for those who have forgotten the theory or just can't immediately recall it. • The airspeed at which an aircraft stalls depends in part on the basic wing loading multiplied by an aerodynamic load factor. For convenience the load factor used is the non-dimensional ratio of lift force being generated to aircraft all-up weight but expressed in terms of 'g' acceleration units. So if the lift force generated is 50% greater than the aircraft's gross weight (while at rest on the ground) the wing structure load factor is expressed as '1.5g'. If a wing reaches the critical angle of attack of 15° or 16° when loaded up — i.e. an aerodynamic load higher than 1g — the stalling speed will be higher than the normal 1g stall speed at that particular mass and wing configuration. The effects of that accelerated stall are usually more pronounced than a 1g stall. An accelerated stall is not a 'high speed' stall — the latter is one form of accelerated stall. A V-n diagram has been modified to show the stall speed positions at a 2g load factor (Vs2g) and a 3g load factor (Vs3g). The manoeuvring speed Va in this particular diagram is coincident with Vs4g. This means that if the pilot, or the atmosphere, attempt to apply a load greater than 4g, at or below this airspeed the aircraft will stall. Thus at speeds at or below Va it is probably not possible to reach the positive limit load factor of 4.4g. • Uncoordinated or cross-controlled flight: applying pressure to the rudder in one direction with opposite aileron applied is cross-controlling. (The cross-controlled situation can also be brought about if the airframe is improperly rigged.) This is normally a rather sloppy way to fly but also a condition that can lead to an uncommanded roll and incipient spin if you inadvertently exceed the critical angle of attack [aoa]; particularly in uncoordinated climbing or lower speed descending turns, such as that made in the approach to landing. A planned and properly executed cross-controlled steady sideslip during final approach IS a normal and safe height loss manoeuvre for non-flapped aircraft. (Some afficionados use sideslip in addition to full flap for a really steep, high drag approach — if it is appropriate and beneficial and if the aircraft designer allows it.) • Once established in a coordinated level turn the lower inner wing has slightly lesser airspeed and thus less lift than the outer wing, which produces a tendency for the outer wing to rise and the bank angle to increase. This requires the pilot to apply a slight opposite pressure to the control column which is known as 'holding-off bank'; this is quite normal and probably the pilot may not notice doing so because it should be just part of maintaining the chosen bank angle throughout the turn. In a climbing turn the outer wing has a slightly greater effective aoa than the inner wing and thus additional lift. Combined with its faster speed this reinforces the tendency for the bank angle to increase and the need to hold-off bank. • However, in a descending turn the steeper path of the inner wing means that it will have a slightly larger effective aoa than the outer; this may compensate, or over-compensate, for the faster velocity of the outer wing. In order then to maintain the required bank angle it may be necessary to apply a slight inward pressure to the control column; i.e. in a coordinated descending turn the bank may be 'held on'. Holding-off bank in a gliding turn can lead to a stall/spin condition. • If an aircraft is inadvertently stalled in a coordinated turn, where the ailerons are in the neutral position, both wings usually display the same progressive stall pattern; thus there should be no pronounced wing drop in a well-designed aircraft. In a coordinated climbing turn you would expect the outer wing to stall first, but propeller effects could negate or reinforce this tendency. • When flying at speeds below 1.5 times Vs — generally regarded as the minimum safe speed near the ground, as long as Vs is calibrated airspeed rather than indicated airspeed; see the following Note 1 — the aileron moments are increasingly less effective with diminishing airspeed, so larger aileron deflections are needed to bank the aircraft. There is always a tendency to be more forceful than necessary, thus overbanking the aircraft at a critical stage. The same applies to rudder effectiveness particularly at low power settings. Note 1: many — possibly most — airspeed indicator systems underread or overread considerably at high angles of attack. If the necessary position error correction to IAS to provide the calibrated airspeed [CAS] has not been supplied by the manufacturer or determined by the homebuilder, there is potential for serious misjudgement. For example, if the indicated Vs is 30 knots and there is a position error of minus 8 knots at that aoa, then the corrected stall speed is 38 knots CAS. Consequently if the pilot calculates the minimum safe speed as 1.5 times 30 = 45 knots then the expected 50% safety margin might be only 20%; i.e. 45/38=1.2 times Vs [CAS]. Of course 45 knots IAS will probably not be 45 knots CAS so there is another adjustment in the calculation, but you get the picture. • In the following text 'top/bottom rudder' refers to the relative position of the rudder pedals when turning; 'top' being the rudder pedal opposite the lower wing, thus if the aircraft is banked and turning to the left then pressure on the right rudder pedal will apply top (or outside) rudder, and pressure on the left rudder pedal will apply bottom (or inside) rudder. An excess of bottom rudder produces a skidding turn; too much top rudder produces a slipping turn or may even halt the turn, so producing a full sideslip. (In a coordinated turn there is just sufficient bottom rudder applied to keep the slip ball centred.) • All of the following is applicable to three-axis controlled aircraft but some parts may not be generally applicable to weight-shift controlled trikes. 6.3.2 Do you know how much the angle of attack increases in a turn? As a consequence of providing the centripetal force for a sustained turn, the wing loading (i.e. lift force) must be increased as angle of bank increases. The loading increases rather slowly up to a bank angle of 30° — where it is 15% greater than normal level flight loading — after which it increases rapidly, where it is 41% greater at a 45° bank angle, and so the load factor will be 1.41g. The right-hand column in Table 3 shows the increase in stall speed, which is proportional to the square root of the load factor. You can see that the percentage increase in stall speed is about half the percentage increase in wing loading. Table 3: wing loading and Vs increase Bank angle Cosine Load factor needed [wing loading increase] Vs multiplier [increase] 10° 0.98 1.02g [+2%] 1.01 [+1%] 15° 0.965 1.04g [+4%] 1.02 [+2%] 20° 0.94 1.06g [+6%] 1.03 [+3%] 30° 0.87 1.15g [+15%] 1.07 [+7%] 40° 0.77 1.30g [+30%] 1.14 [+14%] 45° 0.71 1.41g [+41%] 1.19 [+19%] 50° 0.64 1.56g [+56%] 1.25 [+25%] 54° 0.59 1.70g [+70%] 1.3 [+30%] 60° 0.50 2.00g [+100%] 1.41 [+41% The lift force increase in the constant-speed turn is provided by an increase in the lift coefficient [CL], which in itself is brought about by increasing aoa. Increasing aoa while maintaining constant speed produces an exponential increase in induced drag (this is related to the CL²; perhaps doubled at 45°, trebled at 60°) thus resulting in loss of height or change in rate of climb/descent unless power is substantially increased. A rule of thumb for light aircraft with normally cambered wings is that each 1 degree aoa change — starting from 2° and continuing to about 14° — approximates to a 0.1 CL change and each 0.1 CL increase/decrease at a constant airspeed represents a wing loading change of roughly 8%. So, from the table above, a 30° bank angle in a sustained turn adds 2° to the basic aoa for the airspeed, a 45° bank angle adds 5° and a 60° angle adds 12°. The basic aoa for normal descending and climbing speeds in the circuit are probably in the 6–8° and 6–10° regions respectively so anything more than a moderate 30° banked turn makes severe inroads into the safety margin between the effective aoa of some sections of the wing and critical aoa. As well as that, down-aileron increases and up-aileron decreases the aoa of the outer wing sections. Something to be borne in mind is that wing loading must also change with the payload carried, as do the stall speeds and the performance speeds. If a two-seat recreational aircraft is normally flown with just the pilot on board, the aoa associated with a particular calibrated airspeed is significantly less than when flying at the same airspeed with a heavy passenger and perhaps a full fuel load. For example if the aircraft is normally flown with only the pilot on board with an all-up weight of 400 kg but when flown with a heavy passenger, your gear on board and full fuel then all-up weight increases to 540 kg and the wing loading is increased by 35%. Thus, CL and the aoa for any particular IAS/CAS will be greater than that to which the pilot is accustomed; maybe 2–3° at low airspeeds and much less at high airspeeds. All of this means that the low-speed bank angles you use safely at low weight may well be deadly when heavy. 6.3.3 Do you know why loss of control is more likely if the controls are not coordinated in a turn? If an aircraft is being held in a level turn at a particular bank angle with constant power and excess bottom rudder is applied and held, the aircraft will rotate about the normal axis (yaw) in the direction of rudder deflection. Airspeed over the outer wing increases slightly while airspeed over the inner wing decreases, producing a lift differential; so there will be a secondary roll effect that increases the bank angle. At the same time, the yaw increases fuselage drag — which decreases airspeed and thus lift, and the nose drops a little. This is an uncoordinated skidding turn, which often happens when the pilot tries to 'hurry' the turn with bottom rudder instead of increasing bank and we have a situation where the aircraft is overbanking with the nose yawing inward and downward. If the pilot reacts by applying and holding opposite aileron to restore the required bank angle — i.e. holding-off bank — then, due to the downward deflection of the inner aileron, the outer 30% or so of the lower wing is flying at a much higher aoa than the corresponding section of the higher wing. (If equipped with flaperons the whole lower wing would be flying at a higher aoa.) The lower wing will also be producing more aileron drag — mainly because of the increase in induced drag — so the inward and downward yaw will be increased and there will be a tendency for the pilot to raise the nose by increasing control column back-pressure, thereby increasing aoa overall while, at the same time, speed will continue to decrease because of the increased drag — unless power is increased. The pilot is now 'pushing the aerodynamic limits of the flight envelope'. Any consequent tightening of back-pressure on the control column to raise the nose (or any inadvertent back-pressure applied when, for instance, looking at something of interest below you, looking over your shoulder, being distracted by something in the cockpit, using the radio or even any encountered atmospheric turbulence, wake turbulence from preceding aircraft or gust shear) may take the aoa of the inner wing past the critical angle. The aircraft loses its lateral stability (positive roll damping) and it is most likely that the lower wing will drop in an uncommanded roll, and thus become increasingly more deeply stalled than the upgoing wing — which may not be stalled or just partly stalled. Here is a condensed RA-Aus accident report: "The two seat cabin ultralight stalled and spun just as the aircraft was starting the turn onto base. The pilot halted the autorotation and was very close to complete recovery from the descent with wings level when the aircraft contacted the ground. The very fortunate pilot's later explanation was that just as he was about to turn base he heard another aircraft give a base call. While his attention was diverted into searching for that aircraft speed bled off, control inputs were miscoordinated and the aircraft stalled and started to spin." (The pilot's prompt recovery action also demonstrates it is far better to crash in a nearly level attitude rather than in a nose-down attitude.) If that initial roll is not promptly recognised as an incipient stall or partial stall and allowed to continue — or perhaps incorrectly countered with opposite aileron without first unstalling the wing(s) by easing forward on the control column — the increasing aoa of the lower wing deepens the stall and causes greatly increased asymmetrical drag. Additional yawing forces in the same direction as the lower wing come into play, the nose-down pitching moment increases and the nose drops further. This is the incipient spin condition, where autorotation is about to commence; autorotation will happen quickly, and in some aircraft very quickly indeed. The result is the stall/spin fatality you hear about when an unwary pilot allows a spin to develop without sufficient height to recover; and of course you say 'How sad it is for the family' — while thinking (perhaps falsely) — 'but I'm too wary to get caught by such a simple misjudgement! A similar situation may eventuate if the pilot picks up a dropped wing with rudder without first unstalling the wing (see Picking up a dropping wing with rudder) or if an aircraft taking-off exhibits a wing-rocking tendency (because its airspeed is too low) use of rudder could activate an incipient spin. If the cg is aft of the rearward limit (thus closer to the centre of lift) the amount of elevator deflection or control force needed to rotate the aircraft to the critical aoa is reduced; i.e. just a relatively small rearward movement of the control column may rotate the aircraft to the critical aoa. If MTOW exceeds the design limit and/or the cg is aft of the rearward limit then recovery from the initial stall may be impossible. See the stick force gradient. Apart from the weight and balance aspects, the rule to avoid such situations is in proper energy management — always maintain a safe speed near the ground consistent with the bank angle employed, continually envisage the wing aoa, i.e. keep the wing flying and keep the slip ball centred; and never apply an excess of bottom rudder in an attempt to tighten any turn if height is below the safe recovery height (3000 feet agl perhaps) for a fully developed spin. How often have YOU come within a hair's breadth of eternity while being blissfully unaware of it? Pilots need to be particularly careful when sightseeing. There is always a tendency to overbank the aircraft and pull back too much on the stick ('bank and yank' — perhaps also without adding power) so you or the passenger can get a good view of something on the surface directly below. Extracts from three RA-Aus fatal accident reports: 1. " The pilot was conducting the flight for the passenger to take photographs of the property. Witnesses saw the Drifter fly over the farm buildings at an estimated 300 feet agl and then turn and fly back. The aircraft was seen to do a steep left turn during which the nose lifted. The aircraft entered an incipient spin from which there was insufficient height to recover." 2."The Sapphire was seen to be flying straight and level at about 150 feet agl. The aircraft entered a tight right hand turn, the nose was seen to drop and it appears the aircraft entered an incipient spin subsequently striking the ground in a nose-down attitude." 3."The pilot and his friend intended to do a short photographic flight ... for airport publicity purposes ... the passenger side door of the Skyfox had been removed to allow an unimpeded view for the photographer. No-one witnessed the accident however one pilot ... backtracking the same runway saw the aircraft take-off and start a normal climb but did not see the aircraft from that point as he continued to backtrack. It was only after line-up that he saw the smoke from the crash site. The impact site was 200 metres to the left of the upwind threshold and 900 metres from the start of take-off ... the wings hit almost simultaneously with the aircraft in a near vertical attitude, then bouncing 1.5 metres and coming to rest with the tail against a small tree, 60° nose down, right side up ... facing away from the take-off point ... indicates that the aircraft ... had turned back towards the runway, stalled and spun in with 180° rotation." 6.3.4 Popular precursors to a stall/spin: use rudder to hasten the turn or hold-off bank in a descending turn The precursors to a stall/spin event in a low-power descending turn are the same as those for such an event in a level turn: if an excess of bottom rudder is applied the aircraft will be skidding and, unless some other factor is dominant, whenever an aircraft is slipping or skidding in a turn the wing on the side to which the rudder is deflected will usually stall before the other, with a consequent instantaneous roll in that direction. At descent speeds the aircraft is usually flying at a higher CL, and thus higher aoa, than when on the downwind leg for example. So a reduction in available aoa margin exists before allowing for the additional aoa required for the turn. The descending turn from base leg onto the final approach to landing is the most obvious place for a pilot to attempt to hurry a turn with rudder, because of the need to align with the runway. A tailwind component on base leg to a crosswind landing will increase the tendency to hurry the turn with rudder as may other crosswind situations. If skidding, the excess bottom rudder is yawing the nose down, the rotation about the normal axis reduces lift from the inner wing and increases lift from the outer wing and the tendency is to use elevator to keep the nose up — which is going to bring aoa towards critical. Also because of illusory ground reference cues, there may be a tendency to increase the rate of turn by applying additional bottom rudder whilst maintaining the bank angle with opposite aileron — "holding-off bank". You should never hold-off bank in a descending turn (but see 'Note 2: holding-off bank'). If control column back-pressure is purposely or inadvertently applied the aircraft may enter a cross-controlled stall where it is going to roll further into the bank and enter an incipient spin. In some aircraft it is quite possible that the pilot doesn't recognise that initial roll as an incipient or partial stall and allows it to continue, accepting it as part of the planned turn. The pilot will realise when he/she finds that applying corrective aileron increases the roll rather than reducing the bank. In similar situations there have been cases where the pilot has no doubt wondered why the elevators are completely ineffective when the control column is pulled right back to get the nose up. Apart from the turn from base to final, such stalls might occur on final when avoiding bird strike or attempting a late correction to an out-of-line crosswind approach, or any time when you try to hurry a turn with bottom rudder. Stalls on the final approach, caused by failing to increase power when raising the nose to stretch the approach or reduce a high sink rate, will be exacerbated if the aircraft is also slipping. Possibly the most deadly low-level descending turn is the turn-back following engine failure after take-off. Here is an extract from an RA-Aus serious injury incident report: "The 8000 hour instructor (and student) had just returned from a flight and were over the top of the airfield when he thought the engine hesitated but then continued running. Considerable sink was experienced ... The instructor used rudder to yaw the aircraft toward the short runway then used rudder again to yaw the aircraft more to the right so that a landing could be made on the longest runway. The aircraft stalled and contacted the ground right wing first." If flying cross-controlled when banked with an excess of top rudder — as in the sideslip manoeuvre or a slipping rather than skidding turn — then if it stalls the roll will probably be in the direction of the upper wing; i.e. towards an upright position, which is not quite so alarming and perhaps provides a little more time to react. The following is an extract from an RA-Aus fatal accident investigation. A motor glider was returning to its home airfield after being airborne for about one hour 40 minutes; morning flying conditions were good with a five knot south-easterly. The accident occurred within a ground area considered quite safe for forced landings. The engine, propeller and pylon had been retracted and stowed within the fuselage; in such configuration the motor glider behaves as a pure glider and achieves its best glide ratio of 33:1 at 46 knots and minimum sink rate of 150 ft/min at 40 knots. "The aircraft approached the airport from the west at approximately 400 feet agl, overflew the runway and continued straight ahead. It conducted a left hand turn back towards the runway before entering a stalled state and spiralling one and a half turns into the ground ... approximately 600 metres west of the western airport boundary and 400 metres north of the northern boundary ... it is the opinion of RA-Aus that the accident was attributed to pilot error and lack of situational awareness." Note 2 — holding-off bank. Sailplane pilots probably spend more than 50% of flight time conducting small diameter circling turns within a lift source such as a thermal. The airspeed used to minimise diameter may only be 5–10% greater than the turning stall speed and under these conditions the outer wing tip will be flying at a significantly greater airspeed than the inner wing tip; for a 22-metre wing-span sailplane flying at 44 knots CAS in a 100-metre radius turn, the outer wingtip could be flying at 48 knots while the inner maintains 40 knots. Thus such aircraft develop more lift from the outer wing than from the inner even though the inner wing will have a higher aoa in the gliding turn, so there may be a need for sailplanes to hold-off bank. 6.3.5 What about loss of control in low-level climbing turns? As we saw above, the increased lift force in the turn is provided by an increase in aoa. Now what will happen if you are climbing at Vx (the speed for maximum climb angle) using maximum power and decide — because of rising terrain or other obstruction (the latter particularly occurring in a delayed or misaligned go-around), an approaching aircraft or just natural exuberance — to make a quick 30° left turn using a 45° bank angle, while still maintaining the climb? Coordinated climbing turn: if not keeping a close eye on the ASI and the airspeed has decayed just a little, the general aoa at Vx could be around 12°. To initiate a 45° bank turn, wing loading and thus aoa must increase by 41% which will take the aoa to 17°; i.e. past the critical stall aoa of 15° or 16°. Such full-power stalls in a coordinated climbing turn tend to result in the outer wing stalling first — because in a climbing turn the outer wing has a slightly higher aoa than the inner — with a fairly fast outer wing and nose drop. The roll towards the outside of the turn would initially level the wings but the increasing aoa of the down-going wing continues to accelerate the lift loss and increases the drag on that wing — a particularly rapid action if the propeller torque effect is such that it also reinforces the roll away from the original direction of turn. P-factor may also cause the aircraft to yaw when flying with high power at high angles of attack. Such stalls are likely to result in a stall/spin event if corrective action is not taken as soon as the initial loss of lateral stability — the uncommanded roll, or just a wing rocking warning — is apparent. Cross-controlled climbing turn: if the turn is skidding (excessive bottom rudder applied) then the lower wing may stall first with the consequent roll into the turn — because only one wing is stalled — possibly being sufficiently pronounced to flick the aircraft onto its back. The propeller slipstream from a tractor engine will also be slightly asymmetric supplying more dynamic pressure and thus lift to one wing while reducing the effective aoa. We will discuss cross-controlled climbing turns further when we look at illusory ground reference cues. Climbing at Vx, the best angle of climb speed, should always be regarded as a very short-term emergency procedure. Even a 30° banked climbing turn at Vx might produce an aoa of 14°, very close to the stall aoa and providing no margin for even minor turbulence, slight mishandling or inattention. Of course climb performance will be degraded unless extra power is available, which is unlikely because full power is normally used for the climb until a safe height is reached. The aoa margin that you should always have in hand to cope with such likely events is 3° or 4°, which indicates that, when climbing at Vx, turns should not be contemplated. When climbing at Vy — the best rate of climb airspeed with aoa around 8° — then until a safe height has been gained turns should be limited to rate 1 (3° in azimuth per second or 180° per minute requiring perhaps 15° bank) to ensure an additional margin if wind/gust shear is encountered in the climb-out. When entering a turn during a full-power climb the aircraft must slow, because of the increased induced drag at the higher aoa required to make the turn with no excess power available to counter it. Consequently the aircraft's pitch attitude in the turn must be reduced sufficiently to maintain safe airspeed. Here is an extract from an RA-Aus serious injury incident report: Weather conditions: wind calm, nil turbulence, 23° C. Witness report: "The Gemini took off from the 950 metre runway, and after initially climbing, appeared to slow with a nose high attitude approaching trees. The aircraft was then seen to bank to the left then rotated 180° whilst rapidly losing height before impacting the ground at an approximate 45° angle 100 metres from the runway ... the motor sounded to be operating normally". Elevator trim stall Most light aircraft are not particularly longitudinally stable at approach speeds. At each stage of the landing approach, a flap-equipped aircraft should be properly re-trimmed to maintain the desired airspeed at the current cg position and selected flap configuration and the elevator trim tabs exert quite a large control force at flight speeds. With full flap deflection on the approach some aircraft may need quite an amount of nose-up trim; under these conditions applying full power following a go-around decision may induce a very strong nose-up movement — exacerbated by the elevator trim setting — and this attitude change must be anticipated by the pilot. If the pilot is slow in applying forward stick pressure and adjusting the elevator trim, the pitch-up may result in a highly dangerous 'elevator trim' stall and particularly so if the aircraft is also turning while low in energy. In addition, a 'heavy' aircraft with an aft cg may require considerable forward stick pressure. And, of course, the pilot must make allowance for the normal go-around conditions such as engine torque effects and density altitude. 6.3.6 When a stall with wing drop is recognised, what's the best way to recover? One standard recovery procedure is generally applicable to all stall events or attitude upsets in a three-axis aircraft, whether or not overbanked and/or overpitched — i.e. nose high/low — though this recovery procedure is not applicable to a fully developed spin, whether erect or inverted. Stall recovery generally requires the following concomitant stages: Ease stick back-pressure to reduce aoa of the most stalled wing below critical — which immediately gets the aircraft flying and restores normal 3-axis control. For any aircraft type, the amount of elevator deflection required to unstall the most stalled wing depends on many variables and may range from just an easing of back-pressure to a firm but smooth push towards the neutral position. All aircraft have their own handling idiosyncrasies and pilots must be aware of them. The nose should be positioned sufficiently below the horizontal to achieve safe flying speed while still well clear of the terrain. It's a matter of balancing height loss and proximity to terrain against a quick return to a safe flight speed. If the forward stick movement is both excessive and abrupt, the result could be an aoa movement below the zero-lift aoa, in which case there will be a reversed lift force on the wings that hinders recovery. This may be particularly apparent with trikes. The negative g due to the bunt could adversely affect some engines at a critical time. In instances of extreme overbanking (past 60° or inverted) — where although the upset may be the result of a cross-controlled stall or perhaps wake turbulence — the inverted or near-inverted wing will not be stalled but the aircraft will be in an inverted descent. The forward control column movement is needed to reduce the angle of descent. However, there may be the possibility of an inverted stall if the control column is pushed into its extreme forward position. Warning: never pull BACK on the control column as the initial response to a perceived stall or an overbanked nose-low attitude. Halt downward wing movement with rudder or centre the slip ball. Increase power smoothly, possibly up to maximum. The slipstream will also increase rudder and elevator authority, and aircraft stability, through its effect on fin and horizontal stabiliser; though if the aircraft is near the wings-vertical position — or is inverted — the throttle must be closed. In the recovery from a stall in a climbing turn, full power should be maintained unless the nose is pitched too far down. Roll the wings level with aileron so that all the lift force will be directed away from the ground. If inverted, choose the roll direction that provides quicker return to a wings-level attitude and, of course, the right way up. Following the preceding actions: adjust power as necessary; if flaps were fully lowered then adjust by stages to take-off position; hold attitude until speed has built up to Vy (perhaps Vx if there are terrain problems); then ease into a climb to a safe altitude, where you can assess what went wrong. Never attempt to continue a landing approach after such an event; go around, allowing plenty of time to assess the environment before re-approaching. If the aircraft is properly balanced (i.e. cg is within the limits for that all-up weight), any cross-controlled stall condition is readily countered. Of course if the pilot doesn't wait for the airspeed to build to a safe speed before again applying control column back-pressure, there will be a high risk of a secondary stall which may be very hazardous, depending on the height loss from the first stall. 6.3.7 What are these illusory ground reference cues? It is thought that some ground reference optical illusions may be a contributing factor in loss of control situations near the ground. Such illusions can cause no problem in the circuit if the pilot confines external scanning to the intended flight path and checks for conflicting aerial traffic, while maintaining the appropriate instrument scan and a minimum safe flying speed. The latter is 1.5 times Vs, or perhaps as low as 1.3 times Vs in the latter part of a stabilised final approach as long as 20° bank angle is never exceeded. Fixing the circuit pattern on particular ground reference points, rather than the landing strip (for example "turn downwind around the big tree"), may contribute to illusory ground reference cues. Wind drift illusions When wind speed is reasonably high relative to aircraft speed, then the aircraft's drift with reference to the ground is very apparent to the pilot operating at lower levels, and particularly at short, difficult airstrips. The diagram above represents the ground track of an aircraft conducting a level 720° coordinated turn with constant speed and constant bank angle, such that in the second 360° turn, the aircraft would be encountering its own wake from the first 360° turn — assuming that the wake didn't sink below the flight path. The movement of the air mass in which the aircraft is borne is toward the west (with an easterly wind) and the turn is clockwise when viewed from above. When in the region above the red line, ground speeds will be lower; when below the red line, ground speeds will be higher. The separation of the tracks for each 360° is exaggerated for clarity. When entering the south-west quadrant of the first 360°, the ground speed is initially high but reducing. The drift away from a central ground reference would provide the illusion of skidding out of the turn. Passing through the north-west quadrant, the skidding illusion will disappear as ground speed reaches the minimum. Ground speed starts to increase slightly through the north-east quadrant. However, the increasing drift towards the reference point provides a very noticeable illusion of a slip into the turn. This reaches a maximum as the aircraft enters the south-east quadrant, where it abates as ground speed increases to the maximum. So, in a 360° coordinated level with constant speed and constant bank, the aircraft (and its wake) drifts downwind relative to the ground at the wind speed rate. The cockpit instruments will of course show a constant airspeed, bank angle and a centred slip ball. However, the reference cues seen by a pilot looking at the ground during a low-level turn indicate increasing and decreasing airspeeds, alternating with decreasing and increasing slip into the turn. The downwind turn illusion An unaware pilot may get into a difficult situation in the low-level circuit when an aircraft is turning 90° from crosswind to downwind (as in the progress through the SE quadrant of the diagram above), when drift cues create an illusion of slipping into the turn. At the same time, the increasing ground speed might suggest increasing airspeed. The reaction of an unwary pilot is to increase bottom rudder pressure. This will increase the bank angle and lower the nose. The pilot's reaction may well be to apply opposite aileron to reduce the bank, while increasing control column back-pressure to bring the nose up and possibly reducing power to reduce airspeed. Thus the aircraft is cross-controlled and flying at an aoa with little margin in reserve. This is coupled with decreasing airspeed, reducing lift and the aircraft sinking with a consequent increase in effective aoa. Under such circumstances, there is a likelihood of the aircraft stalling and snapping over. The downwind turn illusion seems to have more potential for error if the aircraft is climbing in a downwind turn, as described previously. Note: sometimes you may read material which purports that an aircraft loses airspeed and might stall when turning from crosswind to downwind because the aircraft is changing direction relative to the wind direction, which of course is nonsense. However, airspeed must decrease in the turn if power is not increased to counter the extra induced drag. Although an aircraft can only stall if the critical angle of attack is reached, a combination of aircraft inertia and a wind shear or turbulence event encountered in the turn could result in a stall (particularly if it is still climbing) or, more likely, a loss of height. If turning very close to the ground to follow a particular ground path (close to trees when stock mustering, for example) the increasing drift into the turn must be allowed for. Pivotal height and reversal height Pivotal height or pivotal altitude is a term used by proponents of ground reference manoeuvres such as 'eights on pylons'. It is one particular height above ground at which, from the pilot's sight line, the extended lateral axis of an aircraft doing a 360° level turn (in nil wind conditions) would appear to be fixed to one ground point, and the aircraft's wingtip thus pivoting on that point. Imagine an inverted cone with its apex sitting on the ground reference point and an aircraft flying around the periphery of its inverted base while maintaining a constant airspeed. The vertical distance from the reference point to the centre point of the inverted base is the pivotal height, and the distance from the edge to that centre point is the turn radius. The bank angle is formed between the outer wall of the cone and the radius line. The pivotal height in nil wind conditions is readily calculated by squaring the TAS in knots and dividing by 11.3. So any aircraft circling at a speed of 80 knots would have a pivotal height (80 × 80 / 11.3) around 550 feet, no matter what the bank angle. In other than still air conditions the pivotal height varies with the ground speed. If the wind was northerly and the aircraft was turning anticlockwise (viewed from above), then ground speed would be lower on the eastern side of the turn and higher on the western side. When in the northern quadrant the aircraft would be drifting towards the centre point, while in the southern quadrant it would drift away. Drift would not be noticeable in the eastern and western quadrants but changed ground speeds would. At 70 knots ground speed, the pivotal height is reduced to 450 feet, at 90 knots it is about 750 feet. (Thus an exercise requiring a continuous 360° balanced turn at constant speed around a ground reference point, whilst holding pivotal height, involves continually changing the height above ground so that the line of pivot around each point is held constantly — rather than maintaining a constant distance from the 'pylon'. The bank angle must also be changed constantly as the wind drifts the aircraft towards or away from the pivot point. It is not an easy exercise to do well, and requires an ability to manoeuvre accurately whilst including the ground reference point in the normal scan pattern. Usually two ground reference points, about five seconds apart, are included for a figure eight pattern — otherwise known as 'eights on pylons'.) Now imagine two cones — the upper one is the inverted cone with the aircraft flying around the edge of its inverted base and below that is a second cone with its base on the ground and its apex connecting with the apex of the upper cone. The vertical distance from the ground through the cone intersection to the centre point of the inverted base is the aircraft height. So when an aircraft is turning at pivotal height in nil wind conditions, the wingtip appears to be fixed to a single point in the landscape. But when at any height other than the pivotal height, the wing tip will appear to move across the landscape. When an aircraft is turning at a height greater than the pivotal height, which is the normal situation in flight, the wingtip appears to move backwards over the landscape — path A in the diagram. However, when an aircraft is turning at a height less than the pivotal height (thus close to the ground), the wingtip appears to move forward over the landscape — path B in the diagram. Thus, when a turning and descending aircraft descends below pivotal height there is an apparent reversal of the wingtip movement from backward to forward, which is the reason why pivotal height is sometimes termed reversal height. There is some thought that the reversal illusion may cause problems to unaware pilots during the final turn on approach to landing, because the turn may well pass through reversal height — at 50 knots ground speed, the reversal height is about 200 feet, at 60 knots it is about 300 feet and at 70 knots it is about 450 feet. If the aircraft is in a banked turn below reversal height, and if the pilot looks down over the wingtip, she/he may get the impression that the aircraft is not turning and may then add additional bottom rudder so that the wingtip then appears to move backwards in the turn — the normal movement. This will cause a yaw and the aircraft's nose will move down, the aircraft may then appear to be nose-low and the pilot's reaction is to increase back-pressure on the control column. Low speed, excessive bottom rudder and an increasing control column back-pressure are the prerequisites for the aircraft to stall and roll toward the lower wing — an entry to incipient spin. All pilots should be aware of this illusion and that wind drift will exacerbate it — the base to final approach turn is probably the most important ground reference manoeuvre that recreational pilots regularly perform. 6.3.8 So how can low-level stall/spin events be avoided? The rules to avoid low-level stall/spin situations are: Always expect the unexpected. (A rather trite statement but, hopefully, it conveys the message.) Good energy management: if potential energy of height is very low then kinetic energy should be reasonably high; i.e. maintain a safe speed (1.5 × Vs1) near the ground. Avoid distraction: maintain a scan appropriate to the situation. Never concentrate on one task, or a ground object/surface scenery, or a search for another aircraft thought to be in the circuit. Envisage the wing aoa while manoeuvring, keep the wing flying and don't exceed 30° bank angle. A good pilot is able to feel the onset of a stall — before any wing-drop — and catch it with just a slight forward stick input. Fly accurately. Keep the slip ball centred and never apply an excess of rudder in an attempt to tighten any turn or change direction. Never turn while still climbing at Vx. Restrict climbing turns at Vy to less than 15° bank angle. 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6.2.1 How fast is too fast? The term 'very high speed' is entirely relative. In an aluminium tube and fabric aircraft it might be 70 knots; in an aircraft that cruises at 100 knots, excessive speed in non-turbulent atmospheric conditions may be less than 130 knots. The airspeed that constitutes 'too fast' can change depending on the load carried and how it is distributed There are limits to the payload an aircraft may carry safely and load must be distributed so that the aircraft's balance — the position of the aircraft's centre of gravity — is contained within defined limits. In addition there is a maximum safe operating weight permitted by the aircraft designer for all flight conditions. So, before you load a 90 kg passenger and 30 kg of gear into your light sport aircraft with full tanks, check the weight and balance charts in your Pilot's Operating Handbook or aircraft flight manual. Weight and balance affect control and stability at all speeds. Excess weight reduces the designed structural load limit factors. Cg positions outside the designated fore-and-aft limits may enhance elasticity reactions to aerodynamic loads, or reduce controllability because of moment arm changes, or delay (even prevent) recovery from unusual and/or high-speed situations. How are airspeed limits, especially Vne, determined? For type certificated aeroplanes FAR Part 23 section 23.335 requires Vd — the 'design diving speed' — to be not less than 1.4 times the design cruise speed for a normal category aircraft. To receive type certification, it must be demonstrated, possibly by analytical methods, that at Vd, the propeller, engine, engine mount, and airframe will be free from over-speeding, severe vibration, buffeting, control reversal and most importantly flutter and divergence. To provide some safety margin, Vne (the IAS that should never be exceeded in level flight, descent or manoeuvre) is set at 90% of the lower of Vd or Vdf. Vdf is a diving speed that has been worked up to by a test pilot and demonstrated to be without problem — though without pulling heavy airframe loads — and which must be lower than or equal to Vd. Vd is not required to be demonstrated in an in-flight test. Vne is always specified in the pilot's documentation as an indicated airspeed and should be marked on the ASI (the red line) but unlike the performance airspeeds (also specified as indicated airspeeds and perhaps marked on the ASI), Vne is related to those structural characteristics and limitations associated with bending, twisting and elasticity, and which affect stability, control and even structural integrity. Limiting speeds are also associated with structural reaction to pilot-induced loads and to gust-induced loads. Limiting speeds could also be associated with other potential problems; for example, suction effects at particular speeds and attitudes might lead to canopy departure, or door or cowling security problems , but normally Vne is limited by the critical flutter speed. Does the indicated speed for Vne stay the same no matter how high you fly? The answer is generally affirmative because the airspeed indicated (Vis) is a reflection of one particular dynamic pressure (½roVis²) no matter what the aircraft's altitude might be. But there is a qualification in that one of the conditions that limits maximum safe airspeed is the onset of flutter, which is a function of the speed of the airflow, the elasticity of the airframe, the balance of the control surfaces and the condition of the flight control actuating systems, rather than just the dynamic pressure. See 'Aerodynamic reactions to flight at excessive speed' but also read 'You can also induce structural damage at moderate speeds!' For most sport and recreational aviation light aeroplanes only one Vne is specified in the Pilot's Operating Handbook or aircraft flight manual. That value is possibly conservative and applicable for operations below 10 000 feet amsl. The designers of most piston-engined GA aircraft specify one fixed-value Vne for operations up to the aircraft's service ceiling; that value is represented by the fixed red line on the ASI. (Note that some EFIS displays may be able to continually adjust the redline display so that it reflects the IAS proportional to a Vne expressed as a true airspeed.) The flight testing program would have determined that the aircraft has no potential flutter problems at Vdf up to the service ceiling. However, some GA aircraft have supplementary lower-value IAS Vne for operations in altitude bands above a stated altitude — perhaps above 10 000 or 15 000 feet. This approach to Vne specification is normal with sailplanes and powered sailplanes whose long, elastic, high aspect ratio wings are likely to develop flutter problems at high true airspeeds, also long wings vibrate less rapidly than short wings, i.e. have lower natural frequencies. Random inflight airflow perturbations may cause wings to bend upward and downward i.e. flap, the degree of oscillation or flapping is more pronounced with high aspect ratio wings. While bending upward the wing adds a vertical velocity* to its forward velocity — the true airspeed — which results in a decreasing angle of attack reducing the lift of the up-moving wing and thus producing an aerodynamic damping of the flapping motion. Similarly the downward flapping motion results in an increasing angle of attack, increasing the lift of the down-moving wing and again producing an aerodynamic damping of the flapping oscillation. *A somewhat similar resultant velocity calculation to a vertical gust encounter. As true airspeed increases the vertical component of a flapping wing's velocity becomes increasingly less significant, so the aerodynamic damping of the flapping oscillation lessens as the aircraft's TAS increases; consequently increasing TAS will increase flutter potential. Where the aircraft designer selects a true air speed value as a limiting airspeed applicable when flying above a nominated altitude, FAR Part 23.1545 (c) requires that "If Vne varies with altitude, there must be means to indicate to the pilot the appropriate limitations throughout the operating altitude range". The 'means' is normally a placard next to the ASI. So, in such circumstances, designers must specify a series of Vne IAS values, corresponding with all possible operating altitude bands. For example, the RA-Aus registered Pipistrel Sinus has the altitude capability of 28 500 feet and can build speed rapidly even in a shallow descent. The Pipistrel designers have deemed it wise to limit maximum speed to a particular TAS at all altitudes. The following table reflects the Sinus flight manual and the ASI placard; the maximum true airspeed target is 122 knots. Note that density altitude rather than altimeter-indicated altitude, is specified — which is significant in Australian climatic conditions. Density altitude/IAS for nominal Vne 122 knots IAS/CAS Density altitude Vne knots IAS 0 122 3300 116 6500 111 10 000 105 13 000 100 16 500 95 19 700 90 23 000 85 26 300 80 If there is insufficient manufacturer's information available for the aircraft you fly — and you are uncertain about the appropriate Vne for an operating altitude — then multiply the density altitude, in thousands of feet, by a factor of 1.5 to get the percentage decrease to apply to the specified Vne to establish a safe Vne appropriate to the altitude. For example if density altitude is 8000 feet and specified Vne is 100 knots then 8[000] × 1.5 = 12%. Corrected Vne = 88% of 100 = 88 knots IAS/CAS. 6.2.2 I like flying my aircraft fast. If I stay below Vne, I won't have to worry about structural failure, right? Vne is assessed at or near MTOW, with the cg at, or within, the fore and aft limits for the aircraft's specified category; it does not apply if weight, manoeuvring loads or cg positions are outside the specified limits. As a maximum airspeed it applies only in reasonably smooth atmospheric conditions for moderate, smoothly applied control movements and symmetrical aerodynamic loads. Even gusts associated with mild turbulence or sudden control surface movements greater than perhaps several degrees travel might lead to some unpleasant surprises, if operating close to but below Vne. Remember that dynamic pressure increases with the square of the true airspeed. At high speed the controls should be quite stiff and are very effective, with a probability of over-control applying extreme loads to the structures. Asymmetrical aerodynamic loads, such as combined rolling and pitching, reduce the maximum allowable airframe load by perhaps 30%. Take care because some aircraft control systems provide inadequate feedback of the load being exerted; i.e. a high load can be applied at high speed with a relatively low stick force, see 'The stick force gradient'. (The effect of gust loads is expanded in the section on wind shear and turbulence.) If an aircraft is operated within its specified manoeuvring and gust envelopes and weight and balance limits — observing the limiting accelerations and control movements, and maintaining airspeeds commensurate with atmospheric conditions — then the only possibilities of inflight control or structural failure relate to: improper modification or repair of the structure control actuating system deficiencies cumulative strain in ageing aircraft, eroding the designed safety margin, remembering that structural fatigue may not have been adequately assessed at the aircraft's design stage failure to comply with the requirements of airworthiness notices and directives poor care and maintenance of the airframe. Flight at airspeeds outside the design manoeuvring flight envelope (or when applying inappropriate control loads in a high-speed descent or, indeed, at any time) is high risk and can lead to airframe failure. Be aware: deliberately exceeding Vne is the realm of the test pilot — who always wears a parachute! The following text is an extract from an RA-Aus accident investigation report illustrating aileron flutter and wing divergence: "(Witnesses) observed the aircraft in a steep dive at what appeared to be full power. The port wing appeared to detach from the aircraft … That wing had the attach points intact but had pulled the mountings out of the top of the cockpit. This action would have released the door, which landed close to the wing. The wings were intact but the ailerons were detached. There was no delamination of the fibreglass structure. The ailerons were not mass-balanced. The aircraft was a conventional design being a high-wing, monoplane of composite construction. While the fuselage was a proven design the pilot/builder had designed his own wing, including the aerofoil section. The workmanship was excellent and there is no evidence of any lack of structural integrity. The eyewitnesses reported seeing "a sort of shimmying" from the aircraft. It is believed that this 'shimmying' was aileron flutter, which led to the detaching of both ailerons. This same flutter condition would account for the massive forces required to detach the wing from the aircraft in the manner that occurred. Flutter could have been triggered by the wing aerofoil design combined with the manoeuvre the pilot was conducting, or from the aileron control design … The aircraft suffered a massive inflight structural failure almost certainly caused by severe aileron flutter and the aircraft speed in the dive. Any flutter would have been exacerbated by the lack of mass balancing." 6.2.3 How strong are the aeroplanes we fly? Design regulations Aircraft structures, engineered by aeronautical professionals, are designed for adequate strength and stiffness while being as lightweight as possible. To receive type certification the design of an aircraft must conform with certain standards, including the in-flight manoeuvring loads plus the turbulence or gust-induced loads that the structure must be able to sustain for the category in which the aircraft may be operated. Even if not seeking certification the designer would still conform to the standards, but this may not apply to those aircraft not designed/engineered by professionals. Even design by professionals may not provide a guarantee that the aircraft is safe. Read this United States Federal Aviation Administration special review team report [pdf format] which identified issues with a LSA category aircraft's wing structure, flutter characteristics, stick force gradients, airspeed indicator calibration, and operating limitations. FAR Part 23 is a recognised world standard for light aircraft certification and the following is an extract: "... limit loads [are] the maximum loads to be expected in service [i.e. the highest load expected in normal operations] and ultimate loads [are] limit loads multiplied by [a safety factor of 1.5]. [FAR Sec. 23.301] … The structure must be able to support limit loads without detrimental, permanent deformation. At any load up to limit loads, the deformation may not interfere with safe operation. … The structure must be able to support ultimate loads without failure for at least three seconds …" [FAR Sec. 23.305] In FAR Part 23 the minimum limit load factors that an aircraft must be designed to withstand at maximum take-off weight are: +3.8g to −1.5g (or −1.9g*) for the normal operational category (which would include most factory-built recreational aircraft); +4.4g to −1.8g (or −2.2g*) for the utility category (which includes most GA, and perhaps some RA, training aircraft); and +6.0g to −3.0g for the acrobatic (i.e. aerobatic) category; for light sport aircraft [LSA] the ASTM International standard is +4.0g to −2.0g; sailplanes and powered sailplanes are generally certificated in the utility or acrobatic categories of the European Joint Airworthiness Requirements JAR-22, which is the world standard for sailplanes; aerobatic sailplanes have limit loads of +7g and -5g. *The increased negative g limit load factors for normal and utility category are required if the designer made use of FAR 23 appendix A allowing simplified design load criteria for single-engine aeroplanes less than 2700 kg weight. There is an increasing risk of structural failure when exceeding the limit load factors, and each instance of excessive loading will accumulate airframe strain and add to the failure risk. See 'Metal fatigue in airframes'. We use load factors in terms of both g and total wing loading.There is an amplification of this relating to gust-induced loads, rather than manoeuvring loads, in the article 'Wind shear and turbulence'. Remember that aerodynamic forces increase with the square of the airspeed; i.e. dynamic pressure = ½roVis². An increase in IAS from 125 knots to 150 knots represents a 44% increase in dynamic pressure. Notes: 1. Uncertificated minimum recreational light aircraft, even with their low wing loading, can readily be overstressed just by flying straight and level at maximum speed and increasing load in a pull-up (positive g) or a full push-over (negative g). 2. Many GA aircraft are type certificated in both normal and utility category, and some are certificated in those plus the acrobatic category. In such cases the MTOW, cg limits and limit load factors are not fixed values but vary according to the intended flight operating category. Airframe elasticity All aircraft structures exhibit some degree of elasticity. That is, they deflect a little, changing shape — flexing, bending and/or twisting — under applied aerodynamic loads. Those short-lasting structural distortions also contribute to a change in the aerodynamic forces, so the distortions and forces are mutually dependent. This is particularly so with the wings, tailplane and control surfaces. However, structures usually spring back to the normal position when the load is removed. Aeroelasticity may lead to some problems at high speed, but reducing elasticity means increasing rigidity, which perhaps involves an unwarranted increase in structural weight. So, aircraft structural engineering must be a compromise between rigidity and elasticity. See the notes on 'stress and strain' in the 'Builders guide to safe aircraft materials'. Aircraft design manoeuvring flight envelope The V-n (or V-g) diagram below is a typical representation of a few aspects of a three-axis aircraft's flight envelope. It displays the aerodynamic load factor on the vertical axis — in terms of g acceleration units — between the certificated limit loads for a LSA category aircraft of +4g to −2g, and airspeed would normally be displayed along horizontal axis. The load is that which parallels the aircraft's 'normal' axis (hence V-n); i.e. the load at right angles to both the longitudinal and lateral axes in erect or inverted flight. The structural load limits shown are for symmetrical airframe loading only. They don't apply if a manoeuvring load is asymmetrical; for example, rolling or yawing, while pulling back on the control column, can place excessive loads on parts of the airframe. Asymmetrical loadings might reduce the acceptable limit load by 30%. The 'clean' (i.e. flaps/spoilers stowed) three-axis aircraft can be flown within the speed and load limits of the light green region at any time. It is only possible to manoeuvre a light aircraft in the reduced-g band between +1g and –1g (light blue) for seconds rather than minutes. Controlled flight at speeds less than the Vs1g stall speed may be accomplished with any manoeuvre that 'unloads' the wings; for example, 'push-overs', which reduce apparent weight (make you feel light in the seat). Aerobatic aircraft can be pulled into a full-power vertical climb where the aoa is held close to the zero lift (zero load) aoa until the airspeed drops close to or below Vs1, then rudder and the slipstream energy is used to cartwheel the aircraft through a 180° hammerhead turn into a vertical descent. And of course an aerobatic aircraft would be able to sustain 1g negative (i.e. inverted) flight for a period. The aircraft will stall if flight is attempted outside those aerodynamic load/speed limits defined by the curved lines. It can be operated above the Va manoeuvring speed without limits on smooth control use, and within the olive-green area in light to moderate turbulence, but it should not be operated above Vno (in the yellow area) except in a reasonably smooth atmosphere. If operating in the region outside the structural load limits, or at velocities greater than Vne/Vd, structural distortion then failure may result. All the foregoing is only applicable to a totally airworthy aircraft. If the airframe is not always properly maintained then the design manoeuvring flight envelope is not applicable; nor is it applicable if aerobatics are performed in an aircraft that is not certified for aerobatics. The following are extracts from a report concerning certain engineering aspects of a fatal accident involving a Skyfox CA22. The aircraft had taken off from an airfield some 20 km from the accident site. The aircraft was seen to break-up in flight while overflying the pilot's house. The port aileron (or a portion of it) and the port wing were seen to detach from the aircraft and descend separately and relatively slowly. The fuselage with the starboard wing attached struck stony ground at high speed. Conclusions: "The most probable primary cause of failure was exceedance of the aircraft's structural design envelope, primarily in regard to speed in conjunction with negative load factor due to a gust, leading to compression failure of the forward strut. Aileron flutter, due to an out-of-balance condition, may have been a factor. It seems probable that the aircraft was flying close to, or above, its Vne of 93 knots. The permissable flight envelope is very small, and would not be at all difficult to exceed inadvertently, especially in a shallow descent." Also, read the Coroner's findings in regard to a double fatality following the inflight structural failure of a Drifter aircraft. 6.2.4 Perilous aerodynamic reactions to excessive speed: flutter and other booby traps We all like to experience the sensation of rapidly gaining speed in a dive, however, the pilot must watch the ASI throughout; airspeed builds very rapidly and dive recovery must be initiated well before Vne is reached. Flutter Wing structures are akin to a very-low-frequency tuning fork extending from the fuselage. When a tuning fork is tapped, the fork vibrates at a particular frequency; the stiffer the structure, the higher its natural frequency. The natural frequency of a wing or tailplane structure may apply another limiting airspeed to flight operations related to a self-exciting interaction between elastic, aerodynamic and inertia forces that result in 'flutter' of control surfaces and the structure to which the surface is attached. For example, when the airflow around a wing, tailplane or control surface is disturbed (by aerodynamic reactions, turbulence or pilot inputs) the structure's elastic reactions – twisting and bending – may combine as an oscillation or vibration of the structure that will quickly damp itself out at normal cruise speeds because of the structure's resistance. It is possible that the oscillation does not damp out but is sustained at a constant amplitude (perhaps felt in the airframe as a low-frequency buzz) that is not, in itself, dangerous but may contribute to structural fatigue. At some higher airspeed — the critical flutter speed, where the oscillations are in phase with the natural frequency of the structure — the oscillations will not damp out but will become resonant, rapidly increasing in amplitude. (Pushing a child on a swing is an example of phase relationships and amplification.) This flutter condition is very dangerous, and unless airspeed is very quickly reduced, the increasing aerodynamic forces will cause control surface (or even wing) separation within a very few seconds. For more information on flutter see 'Aerodynamic reactions to flight at excessive speed'. Twisting the wings off! Wing divergence refers to a state where, at the very low angles of attack at high speed where the nose-down pitching moment is already very high, pressure centres develop pushing the front portion of the wing downward and the rear portion upward. This aerodynamic twisting action on the wing structure — while the rest of the aircraft is following a flight path — further decreases the aoa and compounds the problem; finally exceeding the capability of the wing/strut structure to resist the torsional stress and causing the wing to separate from the airframe — with no warning! This could be brought about if turbulence is encountered at high speed. High-speed control reversal: will it always roll in the direction you want? As airspeed increases, control surfaces become increasingly more effective, reaching a limiting airspeed where the aerodynamic force generated by the ailerons, for instance, is sufficient to twist the wing itself. At best this results in control nullification; at worst it results in control reversal. For example if the pilot initiates a roll to the left the downgoing right aileron might twist the right wing, reducing its aoa, resulting in loss of lift and a roll to the right, probably with asymmetric structural loads: all of which would make life difficult when attempting to roll the wings level during the recovery from a high-speed dive. This could be exacerbated if the wing incorporates significant twist or washout, because the aoa of the outer section could be reduced below the normal zero -lift aoa and thus reverse the lift force on that section. Spars may fracture under those conditions. Many of the uncertified minimum ultralights, and perhaps some of the certificated aircraft, have low torsional wing rigidity that will not only make the ailerons increasingly ineffective with speed (and prone to flutter), but also will place very low limits on Vne and allowable wing loadings. Vne may be so low that it can be readily achieved in a shallow descent at normal cruise power. The problem is that in some home-built aircraft Vne may not be known and could be unexpectedly low! Wing washout: handy at low speed, not so good at high speed! Wings incorporating geometric washout have a significantly lower aoa towards the wing tips. At high speed when the wing is flying at low aoa there are high aerodynamic loads over the wings. But, the outer sections could well be flying at a negative aoa and the reversed load in that area — or just a badly distributed load due to the wing shape — will bend the outer wings down, possibly leading to outer spar fracture. Note: it can happen to certified GA aircraft; two recent (Victoria 2007 and Tasmania 2004) high-speed crashes of Shrike Commander aircraft both exhibited simultaneous negative load failure of both main wing spars at their outer splice joints. This aircraft incorporates 6.5° washout. The atmosphere will demonstrate how puny you are: vertical gust shear and gust loads The effective angle of attack of an aircraft encountering an atmospheric gust with a significant component parallel to the aircraft's normal axis (updrafts, thermals, down-currents, downdrafts, microbursts, macrobursts and lee waves) will be momentarily increased if the air movement is upward relative to the aircraft's flight path, or momentarily decreased if the air movement is downward. Thus an updraft will increase CL and lift causing an upwards acceleration of the aircraft, the magnitude of which is largely determined by the aoa change, the aircraft speed (higher speed — greater g load), the design wing loading and the aspect ratio. The higher the aspect ratio, the greater the change in load factor for a given increase in aoa and the easier it is to overstress the wings at high speed. The effects of shear and gust loads are expanded in the section on wind shear and turbulence. And there are other effects to think about! It is not just the preceding items that may provide problems at high speed. The maximum speed may be limited by the ability of the fuselage to withstand the bending moments caused by the loads on the tailplane necessary to counter the wing's high nose-down pitching moment at very low aoa. Also when nearing the zero-lift angle of attack in a high-speed descent, many cambered wings suddenly experience a very strong nose-down pitching moment and the aircraft will 'tuck under' or 'bunt' rapidly. This instability will certainly make any pilot wish they had not been flying so fast. The symmetrical aerofoil wings often used in powered aerobatic aeroplanes don't have this problem. Also the possibility of a runaway propeller in a fast dive is always there for those aircraft with a constant-speed propeller governor. There is nothing much you can do about that except close the throttle and reduce to minimum flight speed by easing the nose up. Once everything is settled down fly slowly, consistent with the default fine pitch stop blade setting, to a suitable airfield using minimum throttle movements. Another problem is the possibility for extreme loads to be applied in a high-speed pull-up. You can also induce structural damage at moderate speeds! Excessive speed is not always a factor in an aircraft structural failure. In Britain, June 2007, a 900-hour Europa Classic (a type that is represented in the RA-Aus aircraft register) suffered an in-flight break-up. Witnesses said the aircraft had been flying normally but then the tailplane started to make significant up-and-down movements. Then the horizontal stabilisers detached from the rear fuselage, and the wings folded up before separating from the aircraft. The engine stopped and the fuselage plummeted to the ground. The primary cause was probably tailplane flutter, possibly initiated by excessive play developing between the stabiliser torque tube and a mass balance arm. Also, for example, mishandled manoeuvring of weight-shift aircraft can lead to a very fast-acting and uncontrollable pitch autorotation or tumble that imposes extreme transient loads on the structure. The following is a condensed version of an Australian Transport Safety Bureau 'Technical Analysis Occurrence Report' into three fatal accidents. Note: the Coroner's findings in relation to the fatal accident near Atherton does not support any view that the accident was caused by pilot mishandling; rather, the Coroner's "preference is towards port side wing tip separation as a consequence of the un-airworthy state of the aircraft ..." An Airborne Edge trike impacted terrain near Atherton, Qld during a 2005 flight. In 2006 a similar Airborne Edge aircraft impacted terrain at Cessnock, NSW. In both instances, RA-Aus initiated safety investigations during which similarities in the structural failures of both aircraft were observed. In addition, a third accident occurring in 1996 near Hexham involving an HGFA registered Airborne aircraft with similar structural failure was identified. ATSB was asked to conduct technical examination and analysis on recovered parts from the Atherton and Cessnock accidents. Information regarding the 1996 accident was taken from coronial findings. In all three accidents, the failure of the main wingspars had occurred near the wingtip. Qualitative analysis of the structural design and loading of the part and the examination of the coronial findings from the Hexham accident, revealed that all main wingspars had failed under negative g loading. Such loading was likely if the aircraft entered or encountered flight conditions outside the manufacturer's specified flight envelope. Examination of material characteristics of the failed wingspars did not show evidence of material deficiencies that could have contributed to these accidents. The manufacturer's operating handbook prohibited all aerobatic manoeuvres including whipstalls, stalled spiral descents and negative g manoeuvres. The manual specified that the nose of the aircraft should not be pitched up or down more than 45 degrees, that the front support tube of the microlight and the pilot's chest limit the fore and aft movement of the control bar, and that the aircraft should not exceed a bank angle of 60 degrees. Review of photographs of the Airborne Edge, indicate that the wing adopts a degree of twist while in flight. Twist will effect the load distribution by shifting some of the lift from the tips inboard (i.e. more lift is generated in the middle of the wing). Given the structural restraint of the tip struts and battens located at the tip of the trailing edge of the wing, the aerofoil at the wing tip must adjust and try to align with the relative airflow. This results in a smaller amount of lift generated near the wing tips due to a reduced angle of attack to the relative airflow. (Or an aoa reduced below the zero lift aoa; i.e. reversed lift ... JB) 6.2.5 How should I recover from flight at excessive speed? Recovery from an erect dive Generally excessive speed can only build up in a dive, though just a shallow descent can build speed — and rate of descent — quite quickly, particularly in aircraft with high L/D. Table 2 is a calculation of the rate of descent after a few seconds at dive angles of 10°, 30° and 45° — for a moderately slippery light aircraft. It can be seen that even a non-turbocharged aircraft entering a 10° or 15° descent from 8000 feet or so could quickly be exceeding Vne. Recovery from an inadvertent venture into the realm of flight near, or even beyond, Vne is quite straight-forward but requires pilot thought and restraint when initiating the recovery procedure, particularly so if the aircraft is turning whilst diving. Considerable height loss will occur during recovery, so restraint is required when the ground is rapidly expanding in the windscreen. Halt the build-up in airspeed by closing the throttle. Unload the wings to some extent by moving the control column to just aft of the neutral position. The aircraft will be difficult to keep in trim but try to keep the slip ball centred — excess rudder at very high airspeed may strain the tailplane and rear fuselage. Gently roll off any bank while using coordinated rudder; this will ensure the total lift vector is roughly vertically aligned. You must remove the bank before easing back on the stick. Maintain that near-neutral control column position to avoid any asymmetric airframe loading arising from simultaneous application of aileron and elevator at high speed. When the wings are level start easing back on the control column until you are near pulling the maximum load factor for the aircraft — perhaps as much as +4g but allow for turbulence. Hold the applied loading near the maximum until the aircraft's nose nears the horizon then level off. The aircraft will have sufficient momentum to reach this position before opening the throttle. Do not pull back so harshly that subsequent to the sudden rotation about the lateral axis the aircraft's momentum (mass × V) ensures it continues along its original flight vector rather than following the curved recovery path. The result produces a very high aoa, which either induces an extremely high load or goes past the critical aoa and prompts a high-speed stall. Both conditions are very dangerous. If the wing stalls, the aircraft is likely to 'snap roll', applying dangerously high asymmetric loads and quickly losing much height. If it doesn't stall, the sudden very high load is likely to pull the wings off. If you have ample height at the commencement of recovery then there is no need to pull the high g — particularly if the atmosphere is bumpy when gust loads, added to the high manoeuvring g, may prove excessive. A problem with this procedure is that most light aircraft do not have an accelerometer fitted, so it is difficult to judge the g being pulled. However, if properly executed 60° steep turns are practised then you can gain some idea of the 2g load on your own physiology. At the higher end, the average fit person will probably start feeling the symptoms of greyout by 4g. Recovery from a spiral dive In a well-developed steep spiral dive, the lift being generated by the wings (and thus the aerodynamic loading) to provide the centripetal force for the high-speed diving turn, is very high. The pilot must be very careful in the recovery from such a dive, or excessive structural loads will be imposed. If back elevator force is applied to pull the nose up while the aircraft is turning, the result will be a tightening of the turn and rapid increase in rate of descent — thus further increasing the aerodynamic loading or possibly prompting a very high speed stall. Reducing power and levelling the wings must start first, with the rudder and elevators held in the neutral position. As the wings become level with the aircraft still diving at high speed, all the lift that was providing the centripetal force may now be directed vertically (relative to the horizon) and if up elevator is applied the aircraft may start a rapid high g pitch-up — even into a half loop. Thus to prevent this the pilot must hold the elevators in the neutral position while rolling level and even be prepared to start applying forward stick pressure even before the wings become level. Remember: the theme common to all problems encountered when moving at very high speed is that there is little or no warning, and little time to do anything about it! The ONLY safe procedure is not to push the high end of the envelope at any height, don't exceed Vno if the atmosphere is exhibiting any other than light to moderate turbulence, and keep the aircraft airworthy. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

6.1.1 'Lies, damned lies and statistics' We seem to have heard of more fatal accidents in recent years. Why are these accidents occurring? Are RA-Aus sport and recreational pilots and/or aircraft less safe than they were in the 1990s? A person believing that fatalities are inevitable in sport and recreational aviation and examining the fatal accident statistics for the five years 2008 through 2012 (an average of 3.6 per annum) might have concluded that the RA-Aus membership — being representative of powered, fixed-wing, sport and recreational aviation — had, perhaps, then been achieving near-reasonable safety results, after taking into account the fading away of the older ultralight types and the continuing introduction of faster, heavier, more complex and less docile aircraft; together with a marked reduction in the average years of experience of the RA-Aus pilot base. The latter is because of the accelerated intake, and training, of new pilot members during the years 2005-2010 — although there was a very high turnover in newer members. But RA-Aus total voting membership peaked at 10 008 in January 2012 and subsequently experienced a net reduction during 2012-2014. The RA-Aus aircraft register also peaked in early 2012 at 3414 and has reduced to around 3200 in early 2015. However with 11 fatal accidents in 2013 the statistics increased to average 5.8 p.a. for the four years 2010 through 2013; then there were 6 fatal accidents during 2014 increasing the 4-year average to 6.5 p.a. Compounding this were 9 fatal accidents during the January through July period of 2015; IF there are no further accidents during August to December 2015 those 9 accidents will increase the 4-year (2012 through 2015) average to 7.3 p.a. The worst period since the mid-1980s, but the year still has 5 months to go! Such cold, bare statistics fail to reflect the family heartache and economic difficulties resulting from fatal accidents and severe injuries – and the distress that ripples out into the wider community. What adds to the distress, for all of us, is the knowledge that so many current and future accidents have been, or will be, assessed as 'pilot error' or 'human error' and the association just seems incapable of doing anything about it! Generally, shortcomings in knowledge, awareness and task management plus misjudgement and/or unwise decision-making or poor planning, and perhaps neglect plus complacency ("we won't bother checking the take-off distance, we'll be OK!) figure prominently as causal factors in those accidents. Accidents also happen when we attempt to operate in circumstances beyond our experience and/or ability. Quite often, just two or three misjudgements, possibly not that significant in themselves and sometimes combined with a bit of bad luck, lead on to a heap of wreckage. And, of course, there are those few occasions where pilot incapacitation is possibly the cause. For those older members be aware that our abilities (including judgemental ability) and both the speed and appropriateness of our reactions does continue to deteriorate as we age, but some tend to deny it to themselves and to others. (Speaking as an octogenerian who has been able to observe the ageing process on myself and acquaintances for quite a number of years). One acquaintance of similar age told me 'I am still licensed but don't fly pilot-in-command any more – found myself making too many small mistakes and figured I'd better quit before I made the big one'. We — the entire sport and recreational aviation community — must do all we can to bring the number of all such accidents to zero. Fatalities are not inevitable, even an engine failure over heavily forested terrain is survivable and, possibly, some forms of pilot incapacitation accidents could be avoided if pilots follow the pre-flight safety and legality check procedures. Non-conformity to the appropriate aircraft maintenance schedule and procedures is high-risk. Of course there are events that an individual pilot might have little control over, such as a bird strike at a critical time or being struck by an overtaking aircraft on final approach, but again, there may be aspects of situational awareness involved. So, the only statistic that sport and recreational aviation should be striving for is 'zero'; no fatal accidents and no disabling injuries. 'Pilot error' The term appears extensively in safety investigation reports but is often a most unsatisfactory summation of an event and its causal factors; in some cases a police accident investigator can be led to conclude, quite incorrectly, that an accident cause was 'pilot error'; see this Findings of Inquest. In the 1980s the International Civil Aviation Organization [ICAO] — the administrative authority for the world's international air transport system — finally accepted the inevitability of some human error in flight, maintenance and other aviation operations. Consequently, in 1989 ICAO introduced a 'human factors' training and assessment requirement for pilots (and others) and circular 227-AN/136 'Training of operational personnel in human factors' was issued. In 2008, RA-Aus, at last introduced human factors to the flight training syllabus. The Australian Civil Aviation Safety Authority also decided that, from 1 July 2009, 'threat and error management' would be added to the existing human factor aeronautical knowledge examinations, within the day VFR syllabus. A Civil Aviation Advisory Publication CAAP 5.59-1(0) 'Teaching and Assessing Single-Pilot Human Factors and Threat and Error Management' was published in October 2008 and is recommended reading. AUF/RA-Aus fatal accident statistics 1985 to 30 July 2015 There were 149 fatal accidents during the 31 year period 1985 through July 2015. The following bar chart shows the annual distribution of those fatal accidents while the chart line has the effect of smoothing the data by displaying a 4-year running average; the first 4-year period commencing in 1985. The ultralight pioneers were having terrible problems in the formative years of the 1980s (roughly one fatality per annum per 250 members). 90% of the fatal accidents then occurred in ANO 95.10 aircraft; the remainder in ANO 95.25 aircraft. There were about 18 fatal ultralight accidents reported to BASI during 1980 to 1984, then 30 fatal accidents in the period 1985 through 1989 during which period membership grew from around 800 to 2200. The recommendations of the House of Representatives Standing Committee on Transport Safety 'Report on Sports Aviation Safety' began having effect in 1988. The fatal accident rate in those years is not comparable with the current recreational aviation scene as, prior to 1988, the aviation regulations stupidly forced those pioneers to confine their operations to that most dangerous altitude band of no higher than 500 feet above ground level. CAOs 95.32 and 95.55 were introduced in 1990. During the 8-year period 1992 to 1999 AUF ordinary (i.e. voting) membership plateaued at around 3500; the membership turnover was low, pilot training — and the improved availability of choice in aircraft — started to take effect and the fatal accident numbers decreased steadily each year. CAO 95.10, CAO 95.25 and CAO 101.55 types each contributed about 25% of the accidents, with the remaining 25% split evenly between CAO 95.32 and CAO 101.28 aircraft. The factory-built types (95.25, 95.32 and 101.55) were involved in 62% of fatal accidents, and the home-builts in 38%. However, in 1998 the advanced 544 kg 'AUF amateur-built (experimental) ultralight' (the 19-xxxx registrations) was introduced, which did much to provide the platform on which the rather astounding AUF/RA-Aus expansion was based. But this expansion also led to an alarming increase in the number of fatal accidents during the period 2000 through 2006. The amateur-built aircraft figured in 47% of fatal accidents, other home-builts in 10% and factory-builts in 43%, reversing the home-built/factory-built distribution of the 1992 to 1999 period. 6.1.2 Are we getting safer? Recent history 2007-2015 No RA-Aus pilot believes that they will die in an aircraft accident, but the fact remains that during the last 5 years – a period of consolidation rather than expansion of membership and aircraft numbers – the average yearly fatalities are seven pilots and two other occupants, about double the deaths in that prior 5-year period of continuing growth. Note: I occasionally mention an accident causing severe injuries in the following notes but those represent only a few of such accidents where pilots and passengers are admitted to hospital with severe – possibly disabling/disfiguring – injuries. I don't have any reliable statistics for such events but I expect they would exceed the number of fatal accidents; ATSB describes a severe injury as one where the person requires hospitalisation within seven days of the accident. In 2007 RA-Aus membership was still increasing at an annual rate around 13%, which resulted in almost 7800 members at the end of the year. Sadly, 2007 ended as our worst year recorded to that date — eight fatal accidents in which 13 people died, eight pilots and five passengers. In addition there were two other accidents where three occupants were severely injured. A passenger died in nearly two-thirds of the fatal accidents, recording a disastrous increase in such casualties. However, 2008 recorded a great improvement. There was only one fatal accident in an RA-Aus registered aircraft during the year, but sadly both occupants died. There were two accidents where the pilots sustained severe injuries. Since the AUF/RA-Aus was established in 1983 there has been one other year (1996) where only one fatal accident occurred. The average number of aircraft on the register during 2008 was 2850, a 230% increase in aircraft since 1996 so, considering that, 2008 was our safest flying year ever. But the combined 2007 and 2008 total was still nine fatal accidents in which 15 people died. The average annual number of fatal accidents for the four-year period 2005-2008 was 4.5 — less than the 6.0 for the 2001 to 2004 period. The 2009 year started very well; there were no fatal accidents in the first seven months and it looked like the human factors training programs introduced in 2008 were starting to produce the required results. Then there were four fatal accidents between August and December. Two of the accidents involved trikes and a passenger also died in one of the trike accidents. In addition, there was a fifth accident where an RA-Aus three-axis pilot died in a trike registered with HGFA. There were five accidents in which an occupant suffered severe injury. So, a year that started with a lot of promise ended very badly; in effect maintaining the historical average annual number of fatal accidents. The number of aircraft on the RA-Aus register at the end of 2009 was 2955 and there were 9186 ordinary members. There were three RA-Aus fatal accidents in 2010 causing the deaths of three pilots and one passenger, while another passenger was severely injured. Four persons were severely injured in three other accidents. The 2011 year started very badly with two fatal accidents in January and continued in that vein throughout the year to total six fatal accidents. The death toll was eight — five certificated pilots, one student pilot under instruction (i.e. an instructor was in command) and two passengers. It was another very bad year, but it could have been horrific — it was only extraordinarily good fortune that there were no serious casualties when an RA-Aus aircraft, with two persons on board, flew into an operating fairground Ferris wheel. See the Australian Transport Safety Bureau final report. There were three fatal accidents in the first half of 2012 but none during the remainder, two of the accidents involved trikes. The death toll was five — two pilots and a passenger in the trikes, an instructor and a pilot-under-instruction in a Sportcruiser (PiperSport). The 4-year moving average accident rate is now 4.0 per annum, much the same as it had been for the previous four years. 2013 was a disastrous year, we experienced a stunning tally of 11 pilot and two passenger fatalities, a magnitude we have never experienced before. Those 11 fatal accidents are just one less than the total accidents during all of 2010, 2011 and 2012 and increased the annual average to 5.8 p.a. for the four years 2010 through 2013. During 2014 there were six fatal accidents in which eight persons died; six pilots, one passenger and one pilot examiner conducting a biennial flight review, increasing the 5-year average to 6.5 p.a. A small child passenger was severely injured in one of the fatal accidents. To date (1 August 2015) there have been 7 fatal accidents in 2015 in which 8 pilots have died, but thankfully no passengers. One of the accidents involved the worst type of pilot error – a mid-air collision between a Thruster and a Drifter flying in company during a local recreational flight, resulting in the death of both pilots. Not included in these figures is a fatal accident in a nominally non-RAAO associated powered-parachute aircraft that had been allocated an RA-Aus registration number for construction. If there are no further accidents during August to December 2015* those 7 (or 8?) accidents will increase the RA-Aus 4-year (2012-2015) average to 7.3 p.a. *Historically the 3rd quarter of the year has the least accidents but there doesn't appear to be any seasonal influence in the accident rate for the 1st, 2nd and 4th quarters, though there is a tradition (but little backing data) that the 4th quarter has the worst record. The powered recreational aviation scene: 36 deaths in the last 31 months! Of course RA-Aus is not the only association where recreational pilots operate powered aircraft under the exemption CAOs. HGFA pilots also operate trikes under CAO 95.10 and CAO 95.32 plus powered hang-gliders and powered paragliders under CAO 95.8. Also there are non-associated pilots who operate outside an RAAO and thus not under an exemption CAO, i.e. the persons who have inadvertently or deliberately allowed membership/registration to lapse or the few who have never bothered to join RA-Aus/HGFA. The rotary wing gyroplanes operated by Australian Sport Rotorcraft Association members have not been included. Using this broader approach to 3-axis and weight-shift controlled powered aircraft operated by RA-Aus and HGFA members – plus the non-associated fliers – then the total fatalities in just the 31 months – January 2013 to July 2015 inclusive – has reached the very disturbing total of 36 persons – 31 pilots-in-command (25 RA-Aus, 5 HGFA, 1 non-associated), one RA-Aus pilot examiner and 4 passengers (3 RA-Aus, 1 HGFA); 29 of the deaths were associated with RA-Aus, 6 with HGFA and 1 non-associated, the latter seems to have, perhaps inadvertently, allowed RA-Aus documentation to lapse. This broader presentation reflects powered recreational aviation as the general public sees it. The answer to the question — "Does it look like recreational aviators are now getting safer and that there is less chance of fatal accidents?" — is that they are most certainly not getting safer, despite the 2008 introduction of human factors training and the more recent managerial measures — and despite some recent RA-Aus board member statements. Four of the recent RA-Aus fatal accidents involved non-recreational stock and station air work operations, which reflects the lack of compulsory training in such work. Assuredly, we are not improving; perhaps the adage 'The more things change, the more they stay the same' is appropriate? Comparison of the RA-Aus accident rate and the total annual flight hours The following bar and line chart is derived from the annual number of RA-Aus fatal accidents and the total annual aircraft flight hours (reported by aircraft owners at the time annual registration is renewed) to provide the number of fatal accidents per 100 000 flight hours. RA-Aus staff, of course, presume that the annual aircraft flying hours reported by the owners is reasonably accurate. The bars* indicate the number of fatal accidents divided by the number of 100 000 flight hour blocks flown that year and the line indicates a four-year running average of the annual rates. * For example, if there were four accidents in a year when 75 000 flight hours were recorded the calculation would be 4/0.75=5.3 accidents per 100k flight hours. The pattern is interesting. The fatal accident rate per 100k flight hours peaked in 2002* and in the 4-year period 2000-2003, when we were averaging nearly 80 000 flight hours per year, the fatal accident rate was 7.2 per 100k hours, which was nearly as bad as the toll in the early 1980s (which prompted the investigation by the House of Representatives Standing Committee on Transport Safety). During the 2004-2007 period flight hours averaged about 110 000 hours annually and the rate reduced to 5.1 per 100k hours. Then in 2008-2011, when flight hours increased to around 155 000 per annum, there was a big improvement to 2.4 accidents per 100k hours. RA-Aus report 482 000 flight hours accumulated during 2012, 2013, 2014 and I have guessed 100 000 hours for the first 7 months of 2015 so with the 29 fatal accidents recorded for that period, then the rate has jumped up again to 5.4 fatals per 100k flight hours, so we seem to be reverting towards where we were in 2004-2007. A very poor result, particularly considering all the work that has been done. *Note: in 2002 the CAO 95.10, 95.25, 101.28 and 101.55 aircraft accounted for about 75% of hours flown, but by 2012 those aircraft represented less than 10% of flight hours. So, what are the reasons? RA-Aus introduced human factors (HF) training in 2008 and from August that year all student pilots were studying HF in their training and all existing Pilot Certificate holders were required to complete an HF course, or just an examination, by August 2010. Obviously RA-Aus pilots are still not getting the message. HF training is part of airmanship development and is not designed to worsen the safety record, so there must be something wrong in the RA-Aus HF training syllabus — and/or lacking in its implementation by the flight schools and/or in the quality assurance assessment outcome — of both the association's HF training for student pilots and the 2010 HF 'examination' of the, then existing, certificated pilots. In addition, there are concerns whether it was appropriate for the RA-Aus board to persist in its long-standing failure to rapidly disseminate some factual information concerning the occurrence of a serious accident, and the later distribution of the RA-Aus accident investigator's report containing the causal factors. The situation has been that the fatal accidents were not mentioned by the Board executive or RA-Aus management in the website news section or the monthly journal 'Sport Pilot'; not even when the member concerned was well known to, and well respected by, the broad membership. The RA-Aus has not negotiated any arrangement with the State Coroners to allow the fast distribution of some factual causal factor information to the membership – for all fatal accidents – without having to wait, possibly up to six years, for the release of just those rather few, non-restricted, coronial findings. The unpublished policy was that it was left to the membership to learn of the event via the public media's uninformed reports and the internet forums' sometimes grossly speculative chatter, and thus the membership learned nothing of real value from the accident, except, when necessary — but very occasionally — an aircraft airworthiness notice might be issued as a result of the RA-Aus investigative work. All they learned is that their elected representatives did not choose to provide factual causal factor information to the members they represented! Certainly, this negative attitude was doing absolutely nothing to improve safety outcomes and the governance of the Association was neglectful of member and passenger safety — including the safety of those members who need to be protected from their own wilful actions, possibly by re-training or grounding them for a period. There has been considerable tumult in the Board during the past few years and this seems to have contributed to an unusually high turnover in Board members and in the staff, reaching the point where concerns about an apparent lack of corporate knowledge are apparent. For example, the RA-Aus President's report appearing in the July 2014 issue of the monthly RA-Aus members' journal 'Sport Pilot' contained this statement: "The data used in the [Aviation Safety Regulation Review Panel] report covers the period 2008 - 2013. Our fatality rate over this period is pretty steady and some could argue that, aside from 2013, it is downward trending. This is somewhat reassuring and suggests that as pilots (and other participants in our sport) we are less likely to be killed today than we were some years back. To me this is a great result." The ASRR report data referred to purposely excluded all weight-shift controlled aircraft (and stated so) and also did not include other fatal accidents that had not been reported to the ATSB, so the report failed to list eight of the fatal accidents that occurred in 2011 - 2013 and of course 2013, with 13 deaths, was the worst accident year ever recorded and assuredly not 'a great result'. The President's rather odd statement disclosed a notable lack of knowledge ot the RA-Aus fatal accident history and consequently would misinform/mislead those RA-Aus members who were not better informed than he. Perhaps the reason the membership is not 'getting the message' is that the reality is not being publicised vigorously enough in the members' monthly journal and in www.raa.asn.au? The RA-Aus safety management system still seems ineffective. See page 12 of CASA's Sport Aviation Self-administration Handbook 2010 for the elements of a safety management system; also see the text of the 2012-2013 and 2013-2014 CASA/RA-Aus Deeds of Agreement in the members section of www.raa.asn.au. Paragraph B.7 in the statement of purpose section of the RA-Aus constitution is a reminder to all ordinary members and all board members. It states: "To set promote and maintain standards of safety for recreational aircraft by the specification and dissemination of information concerning standards of airworthiness for aircraft, standards of workshops and standards of knowledge for pilots and in particular, to specify, impose and enforce standards of skill and competence reactive to all stages of flying operations and to require any Member to meet such standards to the satisfaction of the Association before authorising such Member to engage in flight operations or any stage or aspect thereof and to grant, issue authorise, modify, cancel, suspend or revoke under the rules of the Association for the time being in force certificates and authorisations relating to aircraft, aerodromes, flying instructing and flying schools and to the skill and qualifications of pilots, instructors, navigators, drivers, mechanics and all persons managing, flying, driving, constructing, repairing or otherwise engaged in connection with recreational aircraft or recreational activities and to do all things relating thereto as may be deemed expedient and to make reports and recommendations to any clubs, authorities or persons concerning the same." I leave it to the reader's own experience to judge whether the actions stipulated by paragraph B.7 are currently being carried out and, as B.7 contains the constitution's sole reference to 'safety', does the constitution as drafted really express any concern with the need for an effective safety management system and the ongoing safety (and safety education) of all the membership and their so-called 'informed participant' passengers? Six passengers (plus one pilot examiner and two student pilots under instruction) died during 2011-2014 which raises the point of how is a passenger made aware of the potential risks inherent in sport and recreational aviation so he/she can make an informed decision about their participation? Various rather bland warning placards, not particularly addressed to the passenger, must be displayed in the aircraft cockpit, but that's hardly sufficient. As the association chooses not to report any information regarding persons fatally or severely injured — for the pilot to include in the pre-flight passenger briefing — how can any person, even the pilot, be regarded as well informed? Can a young passenger make an informed decision? The association doesn't even actively pursue the wearing of suitable safety helmets in flight, particularly for passengers. The role of the Australian Transport Safety Bureau All recreational aircraft accidents/incidents are, or should be, reported to the Australian Transport Safety Bureau. Section 12AB of the Transport Safety Investigation Act 2003 states 'the ATSB is not subject to direction from anyone in relation to the performance of its functions or the exercise of its powers'. Thus a coroner cannot control the release of information by the ATSB. Unfortunately ATSB is not a large organisation, perhaps around 100 personnel (it was required to reduce its numbers by about 10% in 2014) and is also responsible for rail and marine safety investigations. It is rather obvious that ATSB lacks the resources to investigate recreational aircraft accidents, fatal or otherwise, and will not do so unless it considers the safety of the general public may have been threatened or private property damaged. ATSB does provide valuable laboratory assistance to RA-Aus investigations in the fields of metallurgical testing, extract of data from avionics etc. *In a May 20, 2013 document titled 'Focusing our investigative resources' Martin Dolan, the Chief Commissioner and CEO of the Australian Transport Safety Bureau wrote: 'We often get asked how we decide whether to investigate a particular accident or incident that's reported to us. ... we direct our investigative resources to accidents and incidents involving operations that have mature safety systems and will likely uncover a safety benefit or improvement for industry and the travelling public. ... As a result, we generally do not investigate private activities such as sport and recreational flying where there is a voluntary acceptance of a higher level of risk. Those sectors of aviation are largely self-administering and have their own investigation capabilities, working with the police and coroners in the case of fatal accidents. ... When an accident has a high public profile, though, that is one of the considerations we openly take account of in deciding whether to investigate. We recognise that the community sometimes expects we will try and find out what happened, even when it's unlikely that we'll learn something to improve safety. ' ATSB perceives RA-Aus as the organisation responsible for investigating RA-Aus fatal accidents, which results in a negative impact on the dissemination of information to the RA-Aus membership because coroners, in turn, only regard the RA-Aus investigators as part of the police investigation team assisting coroners and thus subject to coronial control in respect to dissemination of their fatal accident investigation reports. Our investigators should be regarded as RA-Aus members trained and appointed by RA-Aus management to do the crash investigation on behalf of the general RA-Aus membership and, to some extent, on behalf of the ATSB. The effect of delayed dissemination or non-dissemination of information from coronial investigations The state police services have coronial jurisdiction to manage and control the site of a fatal recreational aircraft accident thereby preventing unauthorised entry, locating deceased or injured persons, arranging attendance of a medical authority and the transport of deceased or injured persons and, subsequently, coordinating the initial accident investigation. Police may invite participation of accident investigators from a recreational aviation administration organisation. Fatalities are reported to the coroner as a 'non-suspicious reportable death' and the police will maintain charge of the aircraft wreckage until all coronial procedures are concluded. The coroner may be a full-time coroner or a magistrate coroner who will advise the officer in charge as to whether or not further police investigation is required and perhaps order a post mortem examination. The coroner will investigate – with the further aid of police, other investigators and witnesses – the circumstances surrounding the death. For a reportable death the law requires the coroner to establish the identity of the deceased; the medical cause of death (e.g. fatal injuries sustained in an aviation accident); when and where the death occurred and the circumstances surrounding the death i.e. what caused, or contributed to, the aircraft accident. After concluding an initial investigation a coroner may issue his or her findings without holding an inquest ('Findings without inquest') but an inquest may be held if the coroner believes it is in the public interest to do so and/or a 'senior' relative of the deceased requests it. The coroner maintains contact with the family during the coronial process. About 15% (22 000 p.a.) of all deaths in Australia are investigated by coroners of which perhaps less than 3000 result in a coronial inquest. An inquest is a public enquiry by a coroner's court into the cause of a death where various persons associated with the event, or persons thought able to provide 'expert' input, are required to attend and be questioned as witnesses. The coroner's findings, whether 'Findings of inquest' or 'Findings without inquest', may include recommendations to authorities in regard to systems, procedures and regulations with the intention of reducing the likelihood of similar accidents in the future. The coroner will also deliver a cause of death document to the state registrar of births, marriages and deaths, thus enabling the family to obtain the death certificate needed to finalise legal arrangements. However a full coronial investigation is a long (sometimes unbelievably long) but worthwhile, legal process. For example, the coroner's findings from the inquest into the death of research scientist Doctor Barry Uscinski provide informative, perhaps disturbing, reading; but the time elapsed between the accident and release of these findings was 50 months. The police investigator's report concluded that the accident was due to pilot error however the coroner had doubts and the family requested an inquest. The Findings of Inquest, determining that the accident was not due to pilot error, can be read at www.courts.qld.gov.au/__data/assets/pdf_file/0005/337622/cif-uscinski-20141229.pdf". The RA-Aus investigator's opinions as an expert witness seem to form the basis of the coronial findings. Surprisingly 'Findings without inquest' might also take a similar period to be published; for example, see the non-inquest findings for the Zenith Zodiac CH601 crash off Surfers Paradise in March 2008. Although this aircraft was VH registered the ATSB passed it on to RA-Aus thus confirming ATSB's good regard for RA-Aus investigative capabilities. RA-Aus was asked to assist the police investigation and it seems the coroner based his findings on the RA-Aus conclusions. The findings were published in October 2014 (6 years and 7 months after the accident) although in January 2009, RA-Aus issued an airworthiness notice AN070109-1 titled 'Compulsory fitment of a secondary canopy locking device, on Zodiac/Zenair/Zenith aircraft canopy'. This AN just states 'Several reports have been received indicating that the canopy fitted to Zodiac/Zenair /Zenith aircraft are opening in flight causing air turbulence around the tailplane and elevators' and does not mention that the death of two persons 10 months earlier was most likely caused by canopy detachment. Choosing this soft approach rather than making a statement providing more impact on RA-Aus members may have been done to avoid pre-empting the coroner's findings however a bit of judicious wording could have informed the membership of the likelihood of canopy detachment being involved in the deaths of two persons. The findings of the inquest into the death of Philip Henry Scholl took 39 months to publish but are well worth reading, particularly for any member contemplating purchase of a second-hand trike. However the bulk of coroners' findings are not publicly available, distribution being restricted to the next-of-kin and perhaps the police and associated investigators. It is not easy to locate the remaining non-restricted coronial findings on the internet; for example the RA-Aus website contains only two references* to coronial findings, one reveals 32 months between the accident and the date of the finding, the other is 54 months. Obviously a report on an event that occurred 4-6 years previously would be regarded as history by most RA-Aus members reading the coronial findings (particularly those many members who joined the association well after the reported accidents). Grossly delayed accident reporting lacks immediacy in its impact on the membership. It appears that the current national standard for coroners’ courts is that no lodgements pending completion are to be more than 24 months old, so perhaps recreational aviation accidents are regarded as less important and tend to drift toward the back-burner. *The fact that the RA-Aus website contains only two references to unrestricted coronial findings is rather strange as one would presume RA-Aus, as active participants in the coronial investigations, would be on the distribution list when the findings are published. Fatal recreational aviation accidents keep accumulating while coronial investigations drag on. The Doctor Barry Uscinski inquiry took 50 months to complete but in a 50 month period between January 2011 and February 2015 inclusive, 29 RA-Aus accidents killed 38 persons and destroyed 30 aircraft. On top of that it was only extraordinarily good fortune that the October 2011 controlled flight collision with an operating Ferris wheel at Old Bar, NSW did not add members of the public at large to the toll. Self-education - a good pilot is always learning The supply of material for self-education is most important. Martin Dolan, the Chief Commissioner and CEO of the Australian Transport Safety Bureau wrote (May 17, 2013 in answer to a query concerning boating accidents): 'In many cases they reflect what we see with smaller aircraft: the same accidents happening over and over. The best way to tackle these problems would seem to involve clear, targeted safety education [JB's emphasis] about how accidents can be avoided – as many of them are easily avoidable.' The RA-Aus constitution should require dissemination to the membership, as one form of safety education, those very valuable RA-Aus investigator reports that summarise the facts and the investigator's conclusions. Accident investigator's reports were last published in the AUF website in 2004. The following are previously published examples of AUF investigators reports, without the photographs. You will note that the reports do not name any persons. Capella 3 November 2002 combination of factors including pilot misjudgement. Chinook 31 May 2003 student pilot lack of capability (and a query on the wisdom of AUF condoning aircraft ownership — para B.7). RANS Coyote 5 July 2003 illegal non-qualified low flying. Drifter 22 February 2003 'get-home-itis' – flight into low-level IMC. Airborne Edge X 19 December 2002 combination of factors including pilot misjudgement (drag effect of external load on glide path). Harrier 23 March 2002 wing divergence due to aileron flutter in aircraft test dive. Bantam B22S 22 February 2005 EFATO turn back. Corby Starlet 4 October 2003 misjudged speed in forced landing. Drifter 30 July 2003 mustering, no low-level training. Recreational aviators are most certainly not getting safer, possibly the biggest problem is that many, perhaps most, pilots seem to have a feeling of invulnerability believing 'it can't happen to me!' We don't need regulatory changes; recreational aviators need more self-motivation and more consistent, continuing self-education – including some shock treatment. Probably only extensive, graphic and persistent publication of the causal factors and the resultant wreckage of all 82 fatal accidents that have occurred since January 2001, plus a link to the relevant coroner's findings if available, might provide sufficient shock value when printed and distributed to all RA-Aus Pilot Certificate holders. Such material, when seen by their own family members, could place additional pressure on recreational pilots to add improved discipline to their flight activities. I expect the families of fatal accident victims, if approached sensitively, would support such publications; I'm sure they would wish to reduce the number of families that will undoubtedly undergo the suffering and hardship that they have experienced. 6.1.3 I'm a good pilot; I have my pilot certificate, my endorsements and 100s of hours; I feel I am competent enough and sensible enough to avoid an accident, why should I worry? Competency is more than making an excellent landing after a calm flight around the area in fair weather. It has been defined as the combination of knowledge, skills and attitude required to perform a task well — or to operate an aircraft safely and in all foreseeable situations. A flight operation — even in the most basic low-momentum ultralight aircraft — is a complex interaction of pilot, machine, practical physics, airspace structures, traffic, atmospheric conditions, planning and risk. When each and every flight is undertaken it is not only the aircraft that should be assessed for airworthiness; the total environment — airframe, engine, avionics, pilot, atmospheric conditions and flight planning (even the simple planning of how a local fun flight will be conducted) — must support the safe, successful conclusion of each operation. A good pilot never stops learning. The remarks of an instructor, following a very hazardous landing on icy grass, are pertinent: "I have been flying for 45 years and been an RA-Aus instructor for 12 years, but that flight taught me THERE IS ALWAYS MORE TO LEARN". Airmanship is the cornerstone of pilot competency. It is the perception — founded on the acquired underpinning knowledge — of the state of that total environment and its potential risks that provides the basis for good airmanship and safe, efficient, error-free flight. Good airmanship is that indefinable something, perhaps just a state of mind, that separates the superior airman/airwoman from the average. It is not a measure of skill or technique or hours flown, nor is it just common sense (i.e. 'good sense and sound judgement in practical matters'); rather it is a measure of a person's awareness of the aircraft and the current flight environment, and of their own capabilities and behavioural characteristics, combined with sound judgement, wise decision-making, attention to detail and a high sense of self-discipline. For example: "The aircraft, with instructor and student on board, was returning to the airfield when a pitch-down occurred; not known to them the elevator control horn assembly had failed. Control stick and trim inputs failed to correct the situation, but a reduction in power did have a correcting influence, although not enough to regain level flight. A satisfactory flight condition was achieved by the pilots pushing their bodies back as far as possible and hanging their arms rearward. A successful landing at the airfield was accomplished." Insufficient perception, poor judgement (e.g.'I think I can make it!' or worse, 'I think I can make it this time!'), complacency (e.g. 'It'll be OK!') and insufficient self-discipline create a pilot very much at risk. 6.1.4 What kind of flying makes up your hours? Do you often practise engine failure procedures, accelerated stall/unusual attitude recoveries, precise turns and so on, or have you just continually repeated the same operation? Do you try to improve your skills in each flight? Are you aspiring to recognise threats and errors, and manage the risk? Most sport and recreational pilots, as with most general aviation recreational pilots, accumulate only a small number of hours each year. The average annual hours currently reported by RA-Aus Pilot Certificate holders, excluding instructors and students, is only 35 hours; which means that about 50% are flying less than 35 hours. Aircraft owners would put in more hours, aircraft hirers less hours. Perhaps 30 to 40 annual flight hours is enough to maintain just those physical flying skills learned at the ab initio flight school — if the pilot has established a program for self-maintenance of that level of proficiency — but maybe not enough to maintain a high level of cognitive skills: for example situation awareness, judgement and action formulation. Note: the average annual hours flown by RA-Aus aircraft during the last 15 years — including the flight school machines — ranges from 44 to 60, but most years are between 50 and 55 hours, though, of course, some might accumulate ten times that number. Of course, at any time, there are numbers of Pilot Certificate holders – even aircraft owners – who may not have flown for 6 months or more and their lack of recency adds significant risk to flight. The difficult decision for many recreational pilots lies in the situation that, for various reasons, they are only able to undertake those few flight hours. Should flying for enjoyment take a back-seat to the imperative for skill improvement and further inflight educational training? In addition, having completed flight theory studies sufficient to pass the basic aeronautical knowledge test and achieve the Pilot Certificate, it seems that many, perhaps most, pilots leave it at that, failing to expand their knowledge by further in-depth studies of flight dynamics — or even ultralight essentials like microscale meteorology. Possibly because it involves sometimes difficult detail rather than the broad-brush approach of the flight school manual, and perhaps assuming that such knowledge will be accumulated through subsequent flight experience — also hoping, I guess, that they will inherently know how to survive every learning experience. For example, here is a learning experience that the trike instructor was lucky to escape from relatively unscathed, as was his paying passenger: "the pilot intended to conduct a trial instructional flight from a grass strip over 250 metres long. The strip was soft after rain but several solo take-offs had been carried out, each clearing the fence at the end of the strip by 75–100 feet. After some test runs with the passenger on board the pilot elected to take-off using a short field technique. The aircraft accelerated until the nose wheel lifted off the ground and then slowed — with the nose wheel sinking back onto the ground. Because he still believed he had sufficient speed in hand, the pilot tried to make it over the fence; but tripped over it. The aircraft was destroyed." Like the 'Sunday driver', many pilots are just continually repeating the same flight experience — each year is much the same as the last — so all they accumulate is a repetition of one year's experience. They have no program of deliberately accumulating advanced knowledge or skills, nor have they really absorbed the safety basics that should have been instilled into them over the years: always maintain a safe attitude and a safe airspeed when operating at lower levels; if the engine has been misbehaving never take off until the problem is identified and fixed; if the engine goes sick in flight, don't try to make it back to base — land as soon as feasible; don't continue flight into marginal conditions; and so on. The bulk of recreational aviation is undertaken by 'amateur' pilots (using the original meaning of the term; i.e. a lover of a particular activity or pastime) with modest piloting skills. But such pilots, whether PPL or Pilot Certificate holders, must still approach aviation with the attitude of a professional. Too many pilots regard their biennial flight review as a bit of a nuisance, rather than demanding from the reviewer a professional in-depth audit of their competency. Beware your 'friend' the examiner who waives the flight check because he/she is satisfied, by 'discussion and observation', that you are competent. Pay to do the check in a two-seater if your own aircraft is single-seat. 6.1.5 So does a safety problem exist with 'experienced' pilots? Some, perhaps many, pilots are just not ensuring that they continue to accumulate adequate post-Certificate knowledge and skills. In short they never really learn much more about flight dynamics and they lack other pertinent knowledge; and worse, they are just not listening and hearing. On the other hand, there are the very puzzling instances, where those who might be regarded as very experienced and knowledgeable, expose themselves to extreme risk — when surely they know the dice are loaded against them? For instance we have the 10 000 hour pilot who lost his life and that of his passenger near the top of the Great Dividing Range, possibly just because he believed "We can make it under the cloud base!" What may have contributed to that belief and may have led to that possible decision? We just don't know; the only certainty was the location of the wreckage. Some accumulated beliefs may be dangerously false. For example, the long-time pilot who is convinced that a very light aircraft, caught in a strong lee-side down-flow, will always be safe because it will 'go with the flow' when the down-flow flattens out near the bottom of the slope. The sound pilot must understand how the environment parts relate and interact with each other, and judge the likely consequences of any action, deliberate non-action or random event. A systematic approach to continuing improvement in airmanship, plus self-discipline and an ability for self-appraisal, is necessary to achieve that understanding. Don't expect that you can enrol for advanced flight training and somehow that training will reduce your risk exposure to minimum levels. Certainly it will help, but risk management/decision-making is very much in your own hands – do not ignore those rather simple rules that have been established by the cumulative experiences of the pilots that have gone before you during the 110 years of powered aviation history. The Flight Manual or Pilot's Operating Handbook for the aircraft model being flown must be fully understood, and the content re-collectable, when needed in an emergency. You must be totally familiar with the fuel and electrical systems. For an aircraft type that is regularly flown every switch, knob and lever position must be instantly locatable and identifiable without having to hunt for it. Can you find the alternate static vent lever by feel only? Every item in the pre-start and pre-take-off check-lists should be physically verified before opening the throttle — EVERY TIME. It's often the pilot who doesn't do the full checks — because he (usually a male) did them only an hour ago — that gets caught out. Every flight should be prepared and conducted correctly and precisely, using procedures appropriate to the airspace class and without taking shortcuts — even if just a circuit and landing or flight over to the neighbour's strip is contemplated. Pilots should be aware that fatigue, anxiety, emotional state — or flying an aircraft that stretches their skill level, or just flying an aircraft they don't like — will affect perception, good judgement and wise decision-making. If you lack flight experience in a wide range of aircraft types you may find that you have insufficient skill to handle an aircraft that introduces new flight behaviour characteristics and which you are flying for the first time, see this Darwin Coroner's finding resulting from a trike accident (14 months previously). Most studies of aircraft accidents or incidents reveal not a single cause but a series of interrelated events, warnings or actions which, being allowed to progress without appropriate intervention, march on to a possibly catastrophic crash site. Sometimes the final trigger may be relatively innocuous, but sufficient in itself to totally remove a safety margin previously eroded by other events. A U.S. Navy pilot once wrote "In aviation you very rarely get your head bitten off by a tiger — you usually get nibbled to death by ducks." However U.S. Navy pilots are well-trained, well-informed, self-disciplined team players who do not expose themselves to those situations where the tiger concealed out there WILL leap out and bite your head off. For example, take the young male pilot, deemed to have been above average at his flight school two years previously and thought likely to become a very capable aviator, who — in a fit of exuberant youthful bravado — succumbed to temptation and took his equally young female friend for a totally illegal non-qualified low flying demonstration in a RANS Coyote and, when a wing-tip hit a fence line, ended two lives before they had hardly begun, and deeply scarred the lives of the people who loved them.Non-qualified low flying is a killer; checking stock, mustering, checking tanks, buzzing houses, beating-up airfields, low-level photography and power line collisions all figure actively in accident reports. Many years ago, the Australian gliding community demonstrated that there were two main cyclic periods (for them) where people were accident prone. This was about the 100-hour mark, where pilots were beginning to think they were immortal, and about 200-250 hours when they were sure they were; being survivors of the incidents of the first period. Other aviation organisations have indicated similar findings in the 50 to 350 hour period. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

To say aviation and turbines is a happy marriage is true−albeit mainly in the airline, business aircraft and helicopter world. Light aviation, especially the ultralight segment, remains essentially a turbine-free field−apart from noble exceptions, in the form of single-engine jets and ‘experimentals’. Now French newcomer Turbotech is on a mission to challenge the dominance of piston engines and−unheard of in this field−is promising turboprop fuel consumption comparable to piston engines. The company also has an interesting turbogenerator proposal for new e-VTOL and electric aircraft. Currently small turboprops are practically non-existent, although Czech company PBS has in its portfolio the TP100, which should soon be ready for aircraft installation (a few units have apparently been delivered to interested aircraft manufacturers). The TP100 is not in focus of this article as it is way too powerful for typical four-seaters and ultralights, producing 241shp (shaft horsepower). Today’s focus is on Turbotech’s brand new product, the TP-R90 turboprop, which is rated at 90kW (120shp)−neatly falling in the ultralight segment, where aircraft are typically powered today by 100-115hp Rotax piston engines. Turbotech is also offering−based on a similar, but smaller turbine core−another interesting powerplant, the TG-R55 turbogenerator−a ‘range extender’ solution for hybrid-electric powered aircraft. Seeking to establish a toehold in the market, Turbotech showcased its products last year at the most important exhibition in the field, AERO Friedrichshafen in Germany. At their booth I met company CEO and founder Damien Fauvet, who described his products to me. It must be said that many exhibitors hype their wares and you find their miracles tend to take a long time till they prove to work, even if the company doesn’t simply disappear prior to them actually coming to the market. However, Damien’s credibility and the very professional look of his company’s products intrigued me−especially the almost unbelievable claim that Turbotech fuel burn would be comparable to existing piston engines−so I decided to take a closer look. By the end of February this year, the company and the engine’s state of development were apparently at least half-way ready to host a visit. While there was the opportunity, I wanted to see the turboprop running and be able to figure out how they managed to dream up a turbine sipping so little fuel. So I dropped in on Turbotech, which is based at Toussus-le-Noble Airport in the western outskirts of Paris. In Turbotech’s offices, Damien showed to me a video of the first tests of the proof-of-concept engine, run in 2016. That day, the turbine was run up to 41.3kW (56hp)−which approximates the cruise power setting for most ultralights−and the fuel flow was 28.7 litres per hour, a specific fuel consumption (SFC) of 557g/kW hr, to use the yardstick preferred by engineers. At a slightly lower power setting of 38.9kW (53hp) the fuel flow dropped to 25.2 lph (507g/kW hr). Discussing the figures with Turbotech technicians, I gathered that these were only the preliminary data, and that the fuel consumption of the second-generation prototype unit now on test would be further reduced with improvements to the igniters, fuel nozzles, EEC (Electronic Engine Control) and many other components, which were far from being developed production items. Damien proved these predictions correct when, just prior to producing this article, I received the data of the second engine, tested in March this year, where the fuel flow figures were−in line with Turbotech’s promises−slashed dramatically. Running at 66.4kW (90.2shp−just over 70% power), the development engine was now burning only 29.4 litres per hour of Jet-A1, an SFC of 354g/kW hr. At 31kW (42hp), the fuel consumption was just 15.2 lph. According to Turbotech, the definitive version will reach its 90kW target rating and will demonstrate a specific fuel burn close to the target of 340g/kWhr−wow! AERO TG-R55 turbogenerator display It shouldn’t be possible... Turbines are generally taken to be compact and lightweight relative to the amount of power they deliver, only fuel-efficient when operating close to their maximum power output and most suitable as high-power units (2,000shp-plus) for aircraft flying at medium to high altitudes. As benchmark for ‘the turbine advantage’, one of the latest arrivals on the turboprop market, the 7,000shp powerplant for the A400M military transporter, is actually more fuel-efficient than the typical diesel car engine. Thanks to its high pressure ratio and turbine operating temperature, it extracts something like forty per cent or more of the energy contained in the fuel. The advantage over piston engines in airliner and commercial aviation applications is very difficult to match in small turbines. One design path−followed widely in the industry−is to scale down big turbines, but this is unfortunately accompanied by great loss in fuel efficiency. According to Daniel Fauvet, simply scaling down established designs would lead to a very low efficiency microturbine “perhaps extracting only around ten per cent of the energy contained in the fuel”. This is the fundamental reason why we do not have on the market small turbines which are as fuel efficient as modern piston engines. The other stumbling block is that the usual business case for a microturbine−given the large financial investment needed and uncertain market−simply doesn’t make any economic sense. evident quality - Turbotech EEC unit ... So how did Turbotech do it? The key to the possible success of small turbines is solving the problem of their fuel efficiency−specific fuel consumption has to be lowered, and drastically so. Turbotech has done its homework and the configuration of its unit has been refined through CFD (computational fluid dynamics), CAD (computer-aided design) and CAE (computer-aided engineering) using Dassault product Catia and Ansys software, Jean-Michel Guimbard leading the mechanical and aerodynamic design aspects. The result is that the Turbotech microturbine operates at 26 to 30 per cent efficiency. It’s not just the turbine wheel design; when I first saw the Turbotech’s TP-R90 and TG-R55 (TP for turboprop and TG for turbo generator) I thought they looked bulky and over-long, giving the impression of being overweight. Other small turbines are way sleeker and shorter. Aha, but within this extra volume lies Turbotech’s unique selling proposition and the main reason for their engine’s parsimonious fuel consumption. In technical terms, the company says its designs are ‘regenerative’ (i.e. heat recuperating) cycle turbines that re-use energy that is otherwise wasted. Using a proprietary, patented heat exchanger, Turbotech has engineered a breakthrough in small turbine design that will surely be a game changer. To appreciate why, you need to understand how a turboprop engine works. In simple terms, the compressor blows air into the combustion chamber where fuel is introduced and the mixture burns continuously. Energy is taken from the combustion gas by passing it through the turbine, which acts rather like a wind, or water mill. The turbine in turn drives the propeller and compressor. All well and good, but as the turbine is an imperfect device, the exhaust gas, emerging at 700°C or more, still contains a lot of energy. Rather than allow this to go to waste, Turbotech circulates the exhaust gas through a heat exchanger (think of it as radiator) that heats−puts energy into−the air flow from the compressor. And the hotter the air going into the combustion chamber, the smaller the amount of fuel you need to sustain operation. To give an idea of how effective this is, in the absence of Turbotech’s heat exchanger, air emerges from the compressor to enter the combustion chamber at 200°C. With the heat exchanger, it is warmed to 530°C, representing a considerable proportion of energy recovered from the exhaust. As they say, there is nothing new under the sun. What Turbotech is doing is novel in the field of small aircraft turbines but not for large ones. There have been several attempts since WWII by big names in the turbine field like Rolls-Royce, Pratt & Whitney and Allison to use heat recuperation in their designs but none of them was successful, as in practice the weight penalty was excessive and they were too bulky and complex (and therefore too expensive) to justify their use. (Sadly forgotten now, British car maker Rover’s turbine powered Le Mans racer was in 1964 fitted with a rotary regenerator that halved its fuel consumption, and the company came close to putting a similarly equipped saloon car in to production−Ed.) Heat exchangers have been used in stationary turbine powerplants, marine applications and even in the Abrams battle tank (1,500hp, 28% thermal efficiency)−all applications where the extra weight and complexity are acceptable and justified by the fuel saving. Aside from the heat exchanger, the TP-R90 and TG-R55 have the same basic architecture as the typical large-aircraft APU (auxiliary power unit)−a single spool turbine in which a single-stage centrifugal compressor and a radial-flow power turbine are mounted on the same shaft. The clever bit is the way Turbotech makes the compressed air follow a considerably longer path through its heat exchanger before coming to the combustion chamber. To achieve a higher temperature exchange ratio, and to contain its total length, the heat exchanger has been ‘folded’, reducing its installed length by half. In this case he compressed air first travels toward the rear, around the outside perimeter of the annular combustor, and through a first stage of the heat exchanger, and is then turned through 180° to flow forward to combustor, making a second pass through the heat exchanger. Closely guarded IP The heat exchanger is Turbotech’s ‘secret weapon’ in slaying the fuel consumption dragon. I have seen it but unfortunately−and understandably−the company has not allowed me to take any images of it, fearing possible theft of intellectual property. What I am at liberty to say is that it comprises thousands of microtubes made of Inconel, approximately 300mm long which are grouped in two packs of cylindrical shape: one outer ring−running cooler and one inner ring−running hotter, being closer to the exhaust gas path. (Inconel is a registered trademark of Special Metals Corporation for a family of austenitic nickel-chromium-based high temperature superalloys that have a low coefficient of expansion) “The key to a successful microturbine is to build the heat exchanger channels using careful design and the right kind of microtubes,” says Jean-Michel Guimbard. “They need to be as light as possible and they have to have a long life-cycle.” Accordingly, the heat exchanger was designed and manufactured to resist vibration and mechanical and thermal stress. The mechanical stress was of particular relevance as the exhaust gas velocity and temperature varies between the two banks of Inconel microtubes. Probably the most important moment in the process of development of the Turbotech powerplant and of the heat exchanger was the contact with the aerospace supplier Le Guellec, which was asked to manufacture the heat exchanger and became a partner and investor in the Turbotech project after it received insight to the project. Le Guellec is manufacturing its own microtubes on a very cost-effective basis. One important side effect of use of the heat exchanger is that the gases exit the turbine way cooler, at 350°C and at lower velocity compared to traditional turbine engines, so the noise and thermal ‘footprint’ are radically lower. The outer metal casing of the heat exchanger doesn’t exceed 250°C, which makes the Turbotech engine suitable for use in UAVs where a minimal heat signature is essential, and for aircraft made of carbon composites which are particularly sensitive to excessive heat. prototype engine Availability and certification Turbotech is testing and refining the TP-R90 and TG-R55 units, which should be commercially available by mid/end of 2021. A more powerful version of the TG-R55, the 90kW TG-R90 is in the pipeline. Almost identical to the turboprop version, this will weigh 64kg dry/74 kg installed, and should be commercially available by mid 2022. The electric generating efficiency is expected to be 23 per cent (from fuel tank to inverter output). EASA certification for all units will be pursued and is expected to follow in two to three years. Capitalising on the low noise and low thermal signature of the TP turboprop, Turbotech is targeting the UAV market and is a considering number of light aircraft applications including experimentals, ultralights and small helicopters. The promised ‘fuel-burn on apar with the best piston engines on the market’ is almost there, as the latest tests confirm. Of course, Turbotech has yet to prove the reliability of their products in everyday use−so important in aviation world−but having the turbine experts they do in their team I’m confident they will succeed. In my opinion, the emerging market of electrically driven aircraft, and especially the countless e-VTOL door-to-door air taxi designs, will be interested in the TG turbine generator as these applications are power-hungry and we’ve spent years forlornly waiting for promised but not yet delivered high density, lightweight batteries. According to Turbotech, multiple TG-R90 units can be coupled together for electric installations demanding 500kW and more−a heaven-sent power pack for new eVTOLs? For my part, I’m already dreaming about a fast European composite ultralight with a TG-R90 under the cowling. Get ready for an exciting Pilot flight test! development turboprop on test A development turboprop Bringing their skills with them To understand how such a small group of people was able to bring the project to today’s status we have to look at the company’s origins. Turbotech is a French start-up founded by four members in 2009. Their secret is that they previously worked for the Safran Group which is today, together with Go-Capital, one of their principal investors. Ile-de-France (the Paris region) and DGAC (Direction Generale de l`aviation civile) have provided further aid in the form of grants. Damien Fauvet developed a proof-of-concept and then sought and found partners among his former colleagues at Safran. The small group consisting of Fauvet (founder), Jean-Michael Guimbard (Co-founder, CFO & CTO turbomachinery), Baptiste Guerin (co-founder, COO) and Marc Nguyen (co-founder, CTO mecatronic) formed the core team that embarked on fund raising. Success was ensured when Le Guellec (precision tubes and profiles) joined the project and started delivering its microtubes. Le Guellec co-founder and CEO Francois Korner is now part of Turbotech’s management team. turboprop schematic The product range Turbotech has as now, two products in their portfolio, the TP-R90 turboprop and the TG-R55 turbogenerator (the R standing in either case for regenerative and the numbers indicating the turbine power output in kW). Both units feature dual fuel injectors and sparkplugs for ignition, are driven by a proprietary EEC (Electronic Engine Control) system. The EECis similar to the FADEC systems on larger turbines and piston engines, and beside turbine control is capable of the logging data from numerous turbine and gearbox/generator sensors as well as controlling a variable pitch propeller on TP units. The projected TBO is 3,000 hours. A variety of fuels can be used, including Jet-A1, diesel fuel, UL91 avgas and biofuel. Stated fuel consumption (Jet A1, cruise power) is 18-25 lph for the TP-R90, and 15-22 lph for the TG-R55. TP and TG units have only two ceramic bearings (1 ball, 1 roller) where ninety per cent of oil flow is used for cooling and only some ten per cent serves for lubrication. The 90kW TP-R90 single-spool turbine drives a propeller trough the propeller gearbox at the turbine intake end, reducing the turbine’s 80,000 rpm to 2,272 prop rpm. The unit is capable of delivering additional 10kW boost power - in total 100kW - supplied by starter/generator mounted on the gearbox. Price: 65,000 Euro (net) A heat exchanger detail gas turbine modules being produced TP-R90 gearbox casing dimension check compresser intake and volute production TP-R90 drawing production TG-R55 drawing The TG-R55 the turbine drives an generator delivering 53kW electric continuous power at generator output (400 to 900V DC or to customers specs). Engine starting is by the generator running in starter mode. The TG-R55 weighs 55/65kg dry/total and has an electric efficiency of 26 percent. According to Turbotech, as the range extender, the 115kg weight of a package of TG-R55 plus 50kg of Jet A1 fuel offers 155kW hr of electric energy, equivalent to the output of 1,000kg of batteries. Price: 70,000 Euro (net)

It costs Martin Hone less to fly and maintain his two aircraft than it does his old farm ute. He is one of the 10,000 Australians who have worked out how to fly for fun, and on the cheap — with a recreational pilot's certificate. With safer aircraft, cheaper training and relaxed rules, flying schools and hobbyists are reporting that more people are taking up flying for recreation. At least those who know about it. Turns out you do not have to be Richard Branson or John Travolta to own your own plane or fly to Crab Claw Island for breakfast. 'Pastime just about anybody can afford' The recreational certificate allows people to fly smaller, simpler aircraft, like this two-seater kit ultralight from Florida.(Supplied: Australian Aviation Archives) Mr Hone grew up riding his bike to Moorabin Airport to watch the planes take off. Worried his eyesight was not good enough or he would never be able to afford it, he put his flying dream behind him. That was until he found Recreational Aviation Australia. Formerly the Australian Ultralight Federation, RAAus provided a window for Australians looking to fly small aircraft for fun in 1983. "It wasn't for the average person effectively to go flying for fun," Mr Hone said. We exploded in popularity An Australian Lightwing GR582 sits at the Top End Flying Club in Darwin.(Supplied: Lloyd Greenfield) Under the recreational pilot's certificate, pilots can fly with one other person in a recreation registered aircraft weighing under 600kg at take-off. They cannot fly at night or charge for their flying services (unless instructing). RAAus CEO Michael Linke said it was not until 2007 when light-sport aircraft — heavier and more sophisticated than their ultralight predecessors — came on the market that Australians took to the air in droves. When it comes to medical requirements, RAAus CEO Michael Linke said the same Austroads private driver's licence health standard applied for recreational pilots. So if you are fit to drive a car, you are fit to operate a RAAus aircraft. You can assemble your own kit plane You can pay anywhere from $5,000 for a two-stroke motor aircraft to well over $200,000 at the upper end.(Supplied: Lloyd Greenfield) It took Josh Mesilane 32 hours and $5,760 to get his certificate. The 34-year-old had just bought a house, started a business and was looking to start a family when he realised his flying dreams in 2018. Before that he had no idea recreational aviation existed. The certificate requires a minimum of 20 hours, five of which are solo hours. With schools typically charging between $200 and $300 an hour, you are looking at a bare minimum of $4,000 for your certificate. A Cross Country endorsement will take an extra 12 hours and allows you to fly anywhere in uncontrolled air space (about 95 per cent of Australia). Ross Kilner flies with his dog Bongo from Robe in South Australia's Limestone Coast.(ABC South East SA: Bec Whetham) Comparatively, a general aviation licence issued by CASA costs a minimum of $16,000 and 40 hours of flight time. When it comes to owning an aircraft you can pay anywhere from $5,000 for your "rag and tube", two-stroke motor aircraft to well over $200,000 on your top end. If you're really good with the tools, you can assemble your own kit plane. The return of old-school bush flying Recreational Aviation Australia offers a maintenance course that allows pilots to maintain their own aircraft. Another way to save money... if you are good with the tools that is!(Supplied: Lloyd Greenfield) Former Air Force pilot Dan Compton has made a business teaching recreational pilots at his airfield in Dubbo, 388 kilometres north-west of Sydney. Despite advancements in aviation and aircraft, he has been inundated with people wanting to experience flying "the way it was". Part of the "survival flying" Mr Compton teaches at Wings Out West is the ability to land anywhere. "Everything other than an airport looks big (and) scary." — Dan Compton(Supplied: Dan Compton) He said it was all too common for people to learn to only fly and land on airports, which is problematic. "Then everything other than an airport looks big (and) scary," Mr Compton said. Oh, the places you'll go! Dan Compton says most of his students are in their 20s and 30s.(Supplied: Dan Compton) Being able to land anywhere gives pilots the confidence to fly anywhere. The Top End Flying Club does a really good job of that. Club member Fiona Shanahan has enjoyed learning to fly in Darwin since moving from Melbourne. "You (can) go out to the Adelaide River floodplains and see buffalo and pigs and kangaroos and birds, all sorts of things," Ms Shanahan said. "Occasionally you can see some crocodiles sitting in rivers… you don't get to see that from the ground." A recreational aircraft flies over the Northern Territory at sunset.(Supplied: Lloyd Greenfield) Weekend fly-ins are a regular occurrence at the club. "It's not uncommon for a group of us to go and fly to Crab Claw Island for breakfast," Ms Parker said. Peter Brookman bought the Keith airfield from council a few years ago. He has two planes in the hangar there.(ABC South East SA: Bec Whetham) Mr Linke said pilots could land just about anywhere — with a few requirements, such as a windsock and indicators. Is it safe? Two young aviators at the Top End Flying Club in Darwin.(Supplied: Lloyd Greenfield) Mr Linke said recreational aircraft were just as safe as CASA aircraft. "They're obviously not as safe and don't have the same controls as Qantas and planes like that — they're carrying 500 people." Amateur-built aircraft must meet similar standards. "They've got to be inspected, they've got to get a second person inspecting when you're putting an aircraft together, you've got to get checks and balances together when you're building the aircraft," Mr Linke said. 'It'd be nice to see women' Mr Compton said most of his students are in their 20s and 30s. Then there are the teenagers looking to get a head start. Fiona Shanahan had no idea she would become an avid pilot when she moved from Melbourne to Darwin for work.(Supplied: Fiona Shanahan) "The most lacking thing here in my school… is female pilots and I think that's generally everywhere. 'We use it to bribe them' Tony Wulff and his wife, Peta, added car seats to the back for their two young kids.(Supplied: Tony Wulff) Tony Wulff, in central Victoria, flies the family's plane Percy from their farm strip at Heathcote. He and his wife, Peta, added two car seats in the back to accommodate their two favourite passengers "They really love it. They sit in the back in their car seats and have their little headsets on and hang out the window," Mr Wulff said. "We use it to bribe them quite regularly.

ACMA – Australian Communications and Media Authority (managers of the RF spectrum) ADF – Automatic direction finding equipment ADS-B – Automatic dependent surveillance – broadcast AERIS – Automatic en route information service (continuous broadcast network) AFRU – Aerodrome frequency response unit A/G – Air-to-ground (communication) AIP – Airservices Australia Aeronautical Information Publication AIP GEN – The general part of the AIP book AIP ENR – The en route part of the AIP book AM – Amplitude modulation AMSA – Australian Maritime Safety Authority (reponsibilities include all search and rescue; see AusSAR) ATC – Air traffic control sector of ATS ATIS – Automatic terminal information system (continuous broadcast) ATS – Air Traffic Services AUF – Australian Ultralight Federation, now RA-Aus AusFIC – Airservices Australian Flight Information Centre [1800 814 931] AusSAR – AMSA's Australian Search and Rescue organisation AWIB – Automatic weather information broadcast AWIS – Automatic weather information system AWS – Automatic weather station CAA – Civil Aviation Act 1988 CA/GRS – Certified air/ground radio service CAO – Civil Aviation Order CAR – Civil Aviation Regulation CASA – Civil Aviation Safety Authority CASR – Civil Aviation Safety Regulation CAVOK – [cav-okay] Ceiling and visibility better than the minimum VMC conditions for VFR flight CB – The 40 UHF citizen's band channels between 476.425 and 477.400 MHz CENSAR – AusFIC Centralised SARTIME database software — see SARWATCH CL2006 – Current Radiocommunications (Aircraft and Aeronautical Mobile Stations) Class Licence COM or COMMS – The aviation VHF communications band: 118.00 to 136.975 MHz COSPAS – The Russian search and rescue satellite-aided tracking system CTA – Control area CTAF – [see-taff] Common traffic advisory frequency (in the vicinity of an airfield) CTR – Control zone ELB – Electronic locator beacon (obsolete system, not Cospas-Sarsat compatible) ELT – Emergency locator transmitter (aviation distress beacon) EPIRB – [e-perb] Emergency position-indicating radio (maritime distress) beacon ERC-L – En Route Chart–low ERSA – En Route Supplement–Australia ETA – Estimated time of arrival FIA – Flight information area FIR – Flight information region (BN and ML) FIS – Flight information service Flightwatch – Callsign of Airservices Australia's on-request flight information service FM – Frequency modulation GHz – Gigahertz – 1 GHZ = 1 billion cycles per second GNSS – Global navigation satellite system GPS – Global positioning system HF – The 12 aeronautical sub-bands, between 2850 and 22000 kHz, in the domestic and international high-frequency networks HGFA – The Hang Gliding Federation of Australia ICAO – International Civil Aviation Organisation ID – Identification (callsign) IFR – Instrument flight rules kHz – Kilohertz: 1 kHz = 1 thousand cycles per second LCD – Liquid crystal display LED – Light emitting diode LOS – Line of sight (distance) MAYDAY – Prefix to an R/T distress broadcast MTOW – [em-tow] Maximum take-off weight MEM – Memory (electronic) METAR – Routine aviation meteorological report MHz – Megahertz: 1 MHz = 1 million cycles per second Multicom – General airfield communications frequency: 126.7 MHz NAV – Aviation VHF navigation facilities band: 108.1 to 117.975 MHz NAV/COM – The inclusive aviation VHF band from 108.00 to 136.975 MHz NDB – Non-directional (radio) beacon OCTA – Outside controlled airspace PAN-PAN – Prefix to a radiotelephony urgency broadcast PCA – Planning Chart–Australia PEP – Peak envelope power PIC – Pilot in command PLB – Personal locator (distress) beacon POB – Persons on board PROG – Program (microprocessor) PTT – Press-to-talk (button or switch) QNH – The mean sea level pressure derived from the barometric pressure at the station location RA-Aus – Recreational Aviation Australia Inc RCC – AusSAR's Rescue Coordination Centre, Canberra RF – Radio frequency RIS – Radar information service (replaced by SIS) R/T – Radio telephony RPT – Regular public transport SAR – Search and rescue SARSAT – Search and rescue satellite-aided tracking system SARTIME – Time nominated by a pilot for the initiation of SAR action if a report has not been received by the nominated unit SARWATCH – Air Traffic Services SAR alerting system based on position reporting, scheduled reportings and other procedures for IFR flights but also includes VFR flights operating under ATS airways clearance or SIS SIS – ATS radar and ADS-B surveillance information service replacing RIS TAF – Aerodrome weather forecast TTF – Trend forecast UHF – Ultra high frequency band: 300 MHz to 3 GHz Unicom – Ground-based private operator aerodrome communications frequency UTC – Coordinated Universal Time VHF – Very high frequency band: 30 MHz to 300 MHz VFR – Visual flight rules VMC – Visual meteorological conditions VNC – Visual navigation chart VOR – VHF omni-directional radio range VTC – Visual terminal chart

5.7.1 Aviation Search and Rescue [SAR] Formation of AusSAR A Ministerial decision was taken in early 1997 to amalgamate the two aviation and the one maritime Rescue Coordination Centres in Australia into a single agency. The report that the Minister acted upon offered a number of reasons for this approach including the fact that modern communications provided the capacity to coordinate aviation and maritime incidents from a single point bringing with it an improved national response capability. A factor influencing this decision was the increasing use of 121.5 MHz distress beacons where the environment of the unit or person in distress was unknown. As a result, the Australian Maritime Safety Authority was given the responsibility and set up Australian Search and Rescue (AusSAR) as one of its divisions. AusSAR assumed the responsibility for aviation and maritime SAR on 1 July 1997 and maintains the national Rescue Coordination Centre (RCC) in Canberra. The Federal Government, as part of its community service obligations, meets the majority of its operating costs. Aviation SAR In general terms, AusSAR coordinates the response to aviation SAR incidents across Australia except where the incident is covered by other specific arrangements such as an Airport Emergency Plan. AusSAR is reliant on a number of external organisations, the distress frequency monitoring satellite system (Cospas-Sarsat) and the public to provide the SAR alerting function. For aircraft, Airservices Australia is the major SAR alerting agency and its staff notify AusSAR when an aircraft is overdue after communications checks on Air Traffic Service (ATS) frequencies fail to make contact. Airservices Australia also notify AusSAR when there is information concerning imminent or known aircraft crashes, missing aircraft, or distress beacon activations detected by aircraft or ATS. Relationship with Airservices Australia There has been some confusion within the aviation community between the roles of AusSAR and Airservices Australia in regard to the SAR function. Airservices Australia provides In-flight Emergency Response and SAR alerting while AusSAR is responsible for SAR response. In-flight Emergency Response includes air traffic staff providing reasonable advice to assist the pilot in-flight to (1) operate in safe airspace; (2) resume normal operations; and (3) land the aircraft safely. SAR alerting by Airservices Australia (or a flight note holder) occurs when a problem is reported with an airborne aircraft, when no contact can be established following a missed report (arrival, departure, position, operations normal, lost contact following frequency change, etc) or at the expiration of a nominated SARTIME. SARWATCH is a generic term covering SAR alerting based on either full-position procedures, scheduled reporting times, or SARTIME. Full-position procedures and scheduled reporting times are only applicable to IFR flights in all airspace classes and most monitored VFR flights operating in controlled airspace. SARTIME is a time nominated by a pilot for the initiation of a SAR action if a report has not been received from the pilot by the nominated Airservices Australia unit. A VFR pilot operating in Class G airspace may nominate a SARTIME to ATS but the progress of the flight is not monitored, though SAR action will be initiated if there is no communication from the pilot cancelling the SARTIME. Rather than nominating a SARTIME with ATS a flight note lodged with a responsible person, who will raise the alarm should the pilot not report in as scheduled, is preferred for VFR Class G operations. 5.7.2 The SARTIME database As part of its responsibilities, Airservices Australia has introduced a centralised SARTIME database (CENSAR) where SARTIMEs are managed for aircraft arriving at or departing from all aerodromes or where a SARTIME has been submitted through a flight plan or by radio communication. CENSAR alerts the operator when a SARTIME has expired, at which time communications checks are commenced. If this process produces no results at the end of 15 minutes then the situation is passed to AusSAR as an Uncertainty Phase (INCERFA). From an Airservices Australia perspective, a SARTIME can only be cancelled or varied at the request of the pilot. Incidental information that the aircraft has arrived safely at its destination cannot be used to cancel a SARTIME. However, this information is passed to AusSAR by the Airservices Australia CENSAR operator along with the declaration of the phase. AusSAR then takes whatever action is required to ensure the aircraft has arrived safely. Although not a required field in the flight plan, a destination telephone number (which may be a mobile phone number) can often bring a declared emergency phase to a quick conclusion. A SARTIME held by CENSAR is cancelled by the pilot via radio to FLIGHTWATCH before changing to the CTAF or (the preferred method) after landing, via a telephone call to CENSAR (1800 814 931), see AIP ENR 1.1 paragraph 67. (Given the similarity between the names CENSAR and AusSAR, it is not surprising that AusSAR is frequently contacted by pilots wishing to amend or cancel their SARTIME.) Other SAR Alerting and Intelligence Sources Other major SAR alerting sources for AusSAR are the public, police, concerned relatives and friends, and people holding flight notes. The effectiveness of the SAR response is directly related to the timeliness, quality, and accuracy of the information that can be provided on missing aircraft to AusSAR. When other people agree to hold SARWATCH on behalf of a pilot, they should be aware of their responsibilities in the event of an incident and be made aware of the AusSAR aviation contact number (1800 815 257). The importance of early advice so that a search can be mounted before last light should not be missed. While the flight note format at AIP ENR 1.10-23 is a good starting point for the type of information required, accurate intelligence is essential for the early location of an aircraft in distress. A detailed description of the aircraft, its occupants, its planned route, a list of safety equipment carried, whether an ELT and/or Personal Locator Beacon were being carried, whether the pilot and/or passengers usually carry a mobile phone, and so on are all valuable details to assist search planners. Personnel at the departure point such as refuellers and/or other aviators are often valuable sources of intelligence in this regard. Obviously, the most difficult SAR event is one where there is no SARTIME and no details. 5.7.3 AusSAR Aviation Activity Levels During the previous month [March 1999] AusSAR conducted two major searches for missing aircraft. The first was a missing Bell 47 with two POB that was overdue on a flight from Coober Pedy to Kulgera. Following a wide search, the crash site was located on the third day but, unfortunately, there were no survivors. Twenty fixed wing and six rotary wing aircraft were involved at one stage during the search. The second major search incident in March started with a concerned wife phoning AusSAR mid-afternoon saying that she had not heard from her husband. Except for crew details, the only information that she could provide was that it was a Jabiru with two POB expected to fly from Casino to Wangaratta that day. Following a rapid intelligence collection process, it was established that the aircraft had departed Casino at 1035 (local time) intending to track via Tenterfield, Moree and Narromine. Three aircraft conducted an initial search along the planned track before dark and a wide area search commenced the following day. Early into the wide area search a helicopter located the crash scene around 0800 (local) in rugged terrain 15 NM east of Tenterfield. Again, there were no survivors. On the second day, thirty fixed wing and fourteen rotary wing aircraft were involved in the search. In addition to major searches, AusSAR was involved in numerous other activities relating to the aviation environment including a double fatality mid-air between a tug and a glider in the Waikerie area, the forced landing of an aircraft at Bungendore and responding to the ditching of a helicopter in the Cairns area with six of the seven people recovered safely. The aviation section of the statistical summary for the month of March shows that there were 741 aviation SAR phases acted upon and 37 incidents (which includes maritime incidents) where aviation assets were tasked. The aviation SAR phases included 128 IFR fail to report and 515 VFR fail to cancel SARTIME. However, the vast majority of the fail to report or fail to cancel SARTIME were 'technical' phases as the aircraft was safe but the appropriate procedures had not been followed to cancel it from the Airservices Australia system. There is obviously a need for education in this area. Although these 'technical' phases are generally resolved quickly, they do impose a heavy workload and displace other staff efforts in improving the SAR system. The real difficulties are when a major SAR action is in progress and staff resources are being stretched to the limit. On these occasions, the number of 'technical' incidents can detract from marshalling the resources required to assist other aviators whom are believed to be in grave and imminent danger. 5.7.4 Informing the SAR System The Requirement It is fashionable to ponder on what the next decades will bring us. In the aviation sector ICAO has been very active in planning the introduction of technological systems that will enhance air traffic management especially on international routes. These types of systems will add a high degree of accuracy to the current aircraft position in the case of emergency and may take the search out of search and rescue (SAR). Some of these technologies may flow down to the regional and general aviation communities but, due to their initial cost, will be some time in coming. In the meantime if you experience an emergency requiring a forced landing or ditching, how can you best ensure you have provided the SAR system with sufficient information for it to render assistance. This will largely depend upon the ability of the SAR system to respond and your actions in providing it with sufficient information to respond effectively. Marshalling the Response The coordination of a SAR response to an incident involving CASA or RA-Aus registered aircraft rests with Australian Search and Rescue (AusSAR) in Canberra. The word coordination is used as AusSAR has no allocated resources to respond to an incident and it seeks the assistance of response assets from the civil sector through standing or informal arrangements. When the civil sector cannot provide the resources or the available resources are unsuitable, AusSAR is then able to seek assistance from the Australian Defence Force. A SAR incident is defined as a specific situation that causes the SAR system to be activated. In general terms, there are two parts to any SAR response with the first being the search and the second being the rescue. Initially, the degree of search planning is determined by the environment in the incident area, the accuracy of the reported location, the elapsed time since the incident occurred and the availability of suitable search assets. This process is informed by the amount and detail of intelligence that can be gained about the missing aircraft. The rescue plan is conducted in parallel and this is generally undertaken by fixed or rotary wing aircraft that have a standing arrangement with AusSAR or are a specialised emergency response unit located in the vicinity. For incidents on the water, marine craft may also be used. With regard to search assets, aircraft are usually used due to their comparative speed that gives them the ability to cover large areas quickly. The number of aircraft involved will be determined by the size of the area to be searched, the capability and endurance of the aircraft being used and the characteristics of the area to be searched. AusSAR maintains an extensive database of general aviation, police, and specialised emergency service aircraft that are suitable for conducting searches. While twin engine aircraft with good visibility, an accurate navigation system, possessing good endurance and the capacity to carry observers are ideal; it depends on the circumstances as to which aircraft are considered suitable especially in rural and remote areas and search operations to seaward. Some of the more recent larger searches have seen a variety of aircraft types and configurations used including single engine aircraft. While there is a mechanism to pay civil owner/operators on a case-by-case basis for SAR operations, there are occasions when private operators volunteer their services at no charge as a service to the aviation community. There are also many trained police, SES and volunteer observers around the country and they become an important part of any large scale SAR operation. The timeliness of a response to an incident depends not only on the accuracy of information regarding the missing aircraft's flight intentions but also on the accuracy of information held in the AusSAR Aviation Database. AusSAR is interested in obtaining all aircraft details from all aircraft owners/operators and readers are asked to submit their details; a proforma for this purpose can be gained by contacting AusSAR. Any information provided will be subject to the Privacy Act 1988 provisions and will only be used for SAR and emergency response purposes. Please call AusSAR on 1800 815 257 for further details. AusSAR is also interested in non-licensed airfields especially those on properties around Australia. Again, a proforma for this purpose can be gained by contacting AusSAR. AusSAR GPO Box 2181 Canberra City ACT 2601 Telephone: 1800 815 257 Fax: 1800 622 153 5.7.5 Pilot pre-flight preparations Building an Intelligence Picture Now that we have the response organised, it's time to take stock about what preparations you have made to assist the situation if you are the unfortunate soul waiting for the SAR system to perform. In addition to your normal pilot-in-command responsibilities, which include regularly reviewing the Emergency Procedures Section of ERSA, the following points would seem appropriate if AusSAR is to build a rapid intelligence picture: How will your flight be reconstructed if you did you did not submit a flight plan to Airservices Australia, or another organisation, or leave a flight note with a responsible person? In the case of the latter, is the responsible person aware of the AusSAR contact number and the importance of last light regarding the conduct of an initial search? Did the flight plan or flight note include a destination or mobile telephone number, and the phone or mobile number of the pilot? Was there a SARTIME submitted to Airservices Australia? Is there a good description of your aircraft available (external appearance description with a recent colour photograph, equipment fit, emergency and survival equipment including whether an ELT is fitted or a Personal Locator Beacon (PLB) is being carried)? Is there someone aware of your experience, qualifications and aviation habits? How will your passengers and their points of contact be identified? Do the passengers have mobile phone numbers that can be used as an alternative means of contact? Other Points of SAR Significance While many aviators carry a PLB, they leave it in their flight bag in a place that is not easily reached while in flight. The briefing of passengers of its location and purpose may be appropriate. BASI recommends that you and your passengers dress for the terrain and not the destination. It is a sign of good airmanship to monitor 121.5 MHz before engine start and after engine shutdown to ensure that your ELT or PLB or others in the area are not active. All distress beacon detections are treated as distress situations and if you or your passengers inadvertently activate your beacon for longer than ten seconds then turn it off and advise AusSAR of the circumstances via ATS frequencies or telephone. There are no punitive measures for inadvertent activations and early advice will assist in the early resolution of a potential incident. Lastly, if you have activated a distress beacon because you are in grave and imminent danger, if you are able don't forget to take measures to be a cooperative target for search aircraft by using signalling devices such as flares, etc, if available. The imprecision of homing devices mean that the general position can often be quickly determined but the exact position, especially in rugged and covered terrain such as that found on the eastern seaboard, can present major difficulties. Conclusion The coordination of the response to aviation SAR incidents is handled by AusSAR from the Canberra RCC and the effectiveness of the response depends not only on the effectiveness of the search but also on the measures taken by the pilot of the missing aircraft to assist AusSAR by leaving an intelligence trail from which the flight can be reconstructed for search planning purposes. SAR alerting is carried out by a number of means with Airservices Australia being the primary advisory agency for aviation incidents for which Airservices Australia has introduced the centralised SARTIME database (CENSAR). A flight plan or flight note with a destination contact number is most important should an aircraft go missing. Early advice, especially in relation to last light, and good intelligence are both vital to the search planners. AusSAR remains committed to providing an effective SAR response service and it seeks your assistance to ensure that its resources are not dissipated on non-SAR incident responses. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

Distress beacons have been used in aviation for many years and, with some flights now being conducted without the lodgement of flight plans or flight notes or reporting progress, there is increasing importance on having an effective distress beacon as a means of last resort to alert the SAR system that you are in grave and imminent danger. The carriage of aviation distress beacons has been the subject of much debate in the past and this article is designed to bring readers up to date on some of the related issues. The Cospas-Sarsat System The Cospas-Sarsat satellite based system provides distress alerting and location information to search and rescue (SAR) authorities in the aviation, maritime and land environments. The system, which has been in operation since 1982, was originally designed to service a discrete distress frequency on 406.025 (generically stated as 406) MHz but the requirement was expanded to include a service on the aviation distress frequency of 121.5 MHz. In the case of the latter, the physical characteristics of the radio frequency and the output signal mean that there is coarser resolution with beacons operating on this frequency compared to those operating on the higher frequency. There has been major penetration of the 121.5 MHz beacons into non-aviation environments because of their relatively low cost. The Cospas-Sarsat space component comprises a minimum of four Low Earth Orbit SAR (LEOSAR) satellites in polar orbit (two Russian Cospas satellites and two US SARSAT satellites with some reserve units) which monitor 121.5 and 406 MHz. Additionally, the Sarsat satellites monitor 243 MHz which is the military aviation distress frequency. More recently, a number of 406 MHz repeaters have been added to satellites in an equatorial geostationary orbit (termed 'GEOSAR') which provide a supplementary source for near instantaneous alerting of a distress alerting signal should the LEOSAR satellites not have the source in view. A more detailed explanation of the Cospas-Sarsat System can be obtained from the Cospas-Sarsat website. Australia, through Australian Search and Rescue (AusSAR), is responsible for operating the nodal Cospas-Sarsat ground segment in the South West Pacific region. This is done by monitoring satellite intercepted signals from three ground stations, termed Local User Terminals (LUTs), in Albany, Bundaberg, and Wellington (NZ). With 121.5 MHz signals, the three elements in the process (ie the beacon, the satellite and the ground station) must be in view of each other. This is often termed 'local' coverage. With the 406 MHz signal, the satellite has the capacity to time tag the digital information and repeat it when it is next interrogated by a LUT. Through this means, 406 MHz beacons provide 'global' coverage. Beacon Terminology There have been a number of conventions used in the past to describe the various types of distress beacons that have been available in the market place. The current [1999] practice is to use Emergency Locator Transmitter (ELT) to describe those that are fitted to an aircraft, Emergency Position Indicating Radio Beacon (EPIRB) to describe those that are designed to float when immersed in water, and Personal Locator Beacon (PLB) to describe the portable units that are designed for personal use. Compatibility of Older Technology Beacons The 1960s saw the emergence of aviation distress beacons that operated on 121.5 MHz. These beacons met the FAA TSO C91 standard and provided an audible tone on the frequency with the likelihood that other aircraft or air traffic services in the area would intercept it and become aware that an aircraft was in distress. A large number of aircraft were fitted with crash activated fixed ELTs during this period and many commercial operators carried the man-portable Electronic Locator Beacons such as the Garret Rescue 99. These systems are not covered by the Cospas-Sarsat system and continue to rely on the aviation sector for SAR alerting purposes. When a decision was taken to extend the Cospas-Sarsat system to include 121.5 MHz, the standard pertaining to aviation beacons was revisited and a new standard (FAA TSO C91A) was set making the beacon emission suitable for intercept by satellite. The new standard was not made retrospective and many aircraft in Australia still have non-Cospas-Sarsat compatible units fitted. Benefits of Later Technology Beacons The 121.5 MHz beacons in current production are relatively lightweight and inexpensive (with lower end of the market PLBs costing in the vicinity of $A200). They provide an affordable alternative to the more expensive 406 MHz beacons, (which currently [1999] cost from $A1600 but expected to get cheaper) but at an operational cost. There are also 406 MHz beacons being released on the market that have an embedded GPS and automatically report the beacon position in digital form via the satellite system when activated. A comparison of the 121.5 MHz versus 406 MHz beacon technologies is shown below: 121.5 MHz 406 MHz Location Accuracy 15 – 20 km [design specification] 2 - 3 km [design specification] Coverage Local – the beacon, the satellite and the LUT must be in sight of each other Global – the satellite has the capacity to store the information and repeat it for subsequent processing Signal Power 0.1 Watt 5 Watts Signal Type Analog audio signal with no identification feature and subject to high false alert rate due to interference signals Digital with encoded identification of beacon registered owner and capacity to overlay externally provided or embedded GPS position Alert Time Depends on location and varies from 2 hours to the system being ineffective outside coverage areas with ambiguous fix positions often being provided on the first pass Near instantaneous with GEOSAR assisting to provide alerting data if a LEOSAR is not in range. The exception is polar regions where very short delays can be expected. Doppler Location One satellite pass but an ambiguous fix position until resolved by other means or another satellite pass Single satellite pass GPS Location Functionality not available 160 m accuracy (if fitted) Homing Aircraft and vessels use the 121.5 MHz audio signal for homing These types of beacons simultaneously transmit on 121.5 MHz for homing purposes As a result of the location of the three LUTs servicing the Australian region, there are approximately fifty satellite passes serviced per day by AusSAR which results in a typical coverage area and average times for detection of a 121.5 MHz beacon. It should be noted that there are areas, mainly in open ocean areas, around the world where there are gaps in 121.5 MHz coverage. Specific areas not covered of interest to Australia include the Antarctic area, the western Indian Ocean, the southern two thirds of Africa, the mid-southern Pacific Ocean and a gap on the regular Australia to United States air route between the Wellington and Hawaii ground sites. The gap in the southern two thirds of Africa is being addressed in two ways. The first is through ICAO which has mandated that international carriers are to be equipped with 406 MHz beacons when operating in Africa and the second is the planned location of a new LUT site in South Africa which is expected to be operational by late 1999. The major implications for general aviation aircraft operating in Australia using 121.5 MHz beacons is that if the beacon is of the older type, then there is a reliance on other aircraft to detect the 121.5 MHz signal and raise the alarm. This may be problematic in many parts of Australia as only the larger commercial aircraft regularly monitor this frequency. If the beacon is Cospas-Sarsat compatible, the system will generally detect the signal but produce an ambiguous fix position either side of the satellite pass. Follow-on passes, collateral information, or the use of aircraft to investigate both possible positions are used to refine the correct distress beacon position. This evolution takes time and the accuracy of the Cospas-Sarsat derived position is less accurate than with the more technically advanced 406 MHz beacon which usually provides an accurate position on the first pass. These beacons are also encoded with the details of the registered owner and, through the GEOSAR supplementary repeaters, provide near instantaneous advice that an emergency situation exists prior to a Cospas-Sarsat satellite pass. If an embedded GPS is fitted, a position will be passed along with this initial alert advice. The time critical nature of an adequate response is a major consideration when considering the safety of life. Recent ICAO Decisions The ICAO Council agreed in March 1999 that new aircraft operated on extended flights over water or flights over designated land areas shall be equipped with a 406 MHz beacon from 1 January 2002 and existing aircraft will be required to carry them from 1 January 2005. The Council also agreed to write to the Cospas-Sarsat governing body recommending that satellite processing of 121.5 MHz signals cease from 1 January 2009. [This came into effect February 2009] There is an expectation that the international maritime community will follow this lead. A decision regarding the carriage of distress beacons by domestic aircraft in Australia rests with CASA. The FAA has announced that, at this stage, it plans not to mandate the carriage of 406 MHz beacons for general aviation aircraft. One of the major reasons for this position is that emerging technologies may have the potential to offer better and more cost effective solutions for this sector of the industry. There has also been some discussion that, given the dense aviation environment experienced in the US, that 121.5 MHz beacons may remain an effective option without the need for satellite monitoring given that all large commercial operators guard this frequency. However, this is not the case in Australia where many remote operations are conducted without SAR details being lodged and where there is a reliance on distress beacons to act as the primary SAR alerting method. For remote area operations, the low frequency of other traffic in the area must be a consideration in the Australian context when selecting a replacement distress beacon. Conclusion Understanding the division of responsibilities between agencies, informing the system when you are in difficulties and understanding the limitations of distress beacon technology are all important aspects of airmanship. The professional response by the aviation community to the numerous SAR incidents that occur around Australia is publicly acknowledged for, without your assistance, the coordination role of AusSAR would be impossible. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

5.5.1 Communications when in difficulties Assess the probable outcomes of the available alternative actions When a non-instrument rated recreational pilot realises that he/she is likely to be in difficulties (very low on fuel, lost or in failing light, encountering low cloud and rising terrain) or is already in difficulty (the engine or a control circuit has failed), the top priorities are: (a) fly the aircraft, (b) continue flying the aircraft whilst running through the pre-planned emergency drills and (c) decide the best landing area. During this period an assessment must be made of the probable outcome in terms of possible injury and/or survival following the landing. If the aircraft is a low-momentum type, is normally controllable, pilot only onboard, visibility is okay and the area is clear terrain with a normal rural population density and road infrastructure, then the landing should not be life-threatening to a reasonably competent pilot. If unable to remedy the fault on the ground, the pilot won't have to walk far to find assistance. In this circumstance many recreational aircraft pilots, particularly those in single-seat taildraggers, would not consider communicating any form of alert except, perhaps, to advise an accompanying aircraft. This brings to mind the RA-Aus pilot who underwent three forced landings, due to engine stoppages, on one journey to NATFLY before he finally made it. On the other hand if the pilot is experiencing control difficulty, or the terrain is rough and/or heavily treed, or in a more remote area, or the type of aircraft is such that it is likely that the landing cannot be carried out without some risk of occupant injury then the pilot would be well advised to initiate a distress broadcast — a MAYDAY call — even if there is little time available. Distress is defined as a situation where — in the opinion of the pilot in command — an aircraft (or vessel, vehicle or person) is in grave and imminent danger and requires immediate assistance. The word 'Mayday', an anglicised version of the French 'm'aider' [help me], was adopted in 1927 as the standard radiotelephony distress call. The VHF frequency chosen, at the pilot's discretion, depends on circumstances and should be that which is most likely to provide a quick response or rapid assistance at the scene. The first choice response station will usually be Brisbane or Melbourne Centre on the flight information area frequency or a terminal area frequency. If aircraft height is such that Air Traffic Services are not contactable and the frequency already tuned is a CTAF and other aircraft or a Unicom operator are known to be listening out then use that frequency (but bear in mind CTAFs are not monitored by Air Traffic Services). In very remote areas another option is the international VHF voice distress frequency of 121.5 MHz, which, though also not monitored by Air Traffic Services, is continually monitored by RPT aircraft and others with a good citizen attitude and the communications equipment capability to monitor more than one frequency; see Boyd Munro's comments. But the pilot's primary task is to fly the aircraft while selecting the best landing site and minimising risk to all persons; it is not productive to stall the aircraft while attempting to change frequencies (or just to find an appropriate frequency) or communicate, and you certainly don't want to risk dropping a hand-held transceiver. Requesting assistance There are circumstances that make some form of alert or urgency communication advisable, even if the pilot doesn't want to ask for help or feels a bit embarrassed about it. (But — in my book — better red than dead.) The pilot who is encountering difficulties might decide to request assistance from the ATC on-request flight information service Flightwatch — if contactable on the flight information area frequency — advising the difficulty, the aircraft's approximate location and the pilot's intentions: without the pilot initiating an emergency status. The Flightwatch operator may arrange to directly assist or may decide to treat the situation as an emergency and declare the appropriate emergency phase — uncertainty, alert or distress. See AIP GEN 3.6. The call format might be: FLIGHTWATCH* THRUSTER ZERO TWO EIGHT SIX EXPERIENCING NAVIGATION DIFFICULTIES IN DETERIORATING VISIBILITY REQUEST NAVIGATION ADVISORY *Note: ERSA-GEN-FIS 3.2 indicates it is not necessary to prefix the generic 'Flightwatch' callsign with the callsign of the ATC unit e.g. 'Brisbane Centre'. If the pilot considers there is some uncertainty and/or urgency in the situation, and that assistance may be needed, then he/she may decide to advise of an urgency condition and initiate a PAN-PAN broadcast — stating the nature of the alert, pilot's intentions and assistance desired. Pan derives from the French 'panne' meaning 'breakdown'. Declaring an emergency in an appropriate situation displays good airmanship — and people do like to help. Read the article 'Salvation from above' in the January–February 2001 issue of the Australian Civil Aviation Safety Authority's Flight Safety Australia magazine. A categorised index of articles of interest to recreational pilots contained in Flight Safety Australia since 1998 is available on this site. The VHF urgency and distress calls PAN-PAN and MAYDAY calls are internationally recognised emergency transmissions that initiate ICAO prescribed procedures and offer decided advantages to the pilot in difficulties. Distress calls have absolute priority over all other communications on that frequency, and the word MAYDAY commands immediate radio silence. Radio silence should continue until listeners have determined that communication has been properly established between the station in distress and a responsible authority, and that assistance is being provided. Similarly PAN-PAN urgency communications have priority over all other communications except distress calls. The Flightwatch flight information service or the ATS alerting service will immediately acknowledge any distress or urgency message received, coordinate communications and alert the Australian Search and Rescue organisation [AusSAR] on receipt of a distress call. If any station monitoring a distress or urgency message becomes aware that Flightwatch either has not received the message or, having received it, cannot establish contact with the originator, that station has a responsibility to contact Flightwatch and/or the aircraft, and offer assistance — possibly as a relay station — which may entail remaining in the area. There is an understanding that "In an emergency requiring immediate action, the pilot in command may deviate from any rule ... to the extent required to meet the emergency." However, you would need to ensure that any such departure doesn't cause risk to someone else. Nothing in the CASRs acts to protect the pilot against civil liability in the case of damage to persons or property. Also declaration of an emergency while entering an active restricted area does not guarantee safe passage. For transponder-equipped aircraft also see transponder emergency procedure. MAYDAY call format To remove any uncertainty whether a monitored call is an emergency call, it is most advisable to precede the call with the recognised priorities PAN-PAN or MAYDAY, then transmit as much of the following detail as circumstances allow — bearing in mind the pilot's first priority is to fly the aircraft. If experiencing controllability problems or an engine failure when close to the surface, there won't be much time to bother about formal communication formats. If time is available, distress calls have the preferred format: Priority = MAYDAY (repeated three times) Calling station ID (repeated three times, if time permits) and aircraft type Nature of distress Calling station position, heading and altitude Intentions Other useful information For example, with an engine failure over rough, hilly terrain: MAYDAY MAYDAY MAYDAY THRUSTER ZERO TWO EIGHT SIX / ZERO TWO EIGHT SIX / ZERO TWO EIGHT SIX ENGINE FAILURE ESTIMATED POSITION THREE ZERO MILES SOUTH EAST ALBURY / HEADING EAST / NOW DESCENDING THROUGH THREE THOUSAND INTEND FORCED LANDING IN MITTA VALLEY TWO POB / THRUSTER ZERO TWO EIGHT SIX / MAYDAY Note the last line includes the information that there are two persons on board [POB] and repeats the call sign and the MAYDAY priority. It might help an Air Traffic Services operator, managing several frequencies, if the frequency in use was also transmitted. PAN-PAN call format Urgency calls have the preferred format: Priority = PAN-PAN (three times) Called station ID Calling station ID and aircraft type Nature of emergency Calling station estimated position, altitude and heading Request or intentions Utilising GPS If the pilot in distress is able to communicate, or has established contact, a functioning GPS is a great advantage to everyone concerned, because the pilot is then able to provide a latitude and longitude position probably accurate to 100 metres. Consequently any search only entails a direct flight to that position by one aircraft. Some distress beacons also include Global Positioning System input capability. Other communication means UHF citizen's band [CB]. In rural and outback areas, particularly in the vicinity of the arterial roads, there is widespread usage of UHF CB radios by truck drivers, four-wheel drive vehicles, road crews, mustering crews and fencers. There are 40 CB channels located between 476.425 and 477.400 MHz in 0.025 MHz steps. The road vehicles listen out on channel 40, and channels 5 and 35 are emergency frequencies. Some VHF handheld transceivers might include UHF CB capability and there is quite a good UHF repeater system (channels 1–8/31–38) established in Australia. A cellular mobile communication device may be useful in advising your situation to others. An individual's ability to make radio frequency transmissions in the Australian cellular mobile communications 850, 900, 1800 and 2100 MHz bands is legitimised by the Radiocommunications (Cellular Mobile Telecommunications Devices) Class Licence 2002. An activated mobile communication device in a high-speed aircraft may cause channel interference across cells, but in July 2010 the Australian Communications and Media Authority [ACMA] amended the class licence (which previously prohibited the airborne use of mobile communication devices) to allow operation of a mobile communication device in an airborne aircraft above an altitude of 10 000 feet or, perhaps, 20 000 feet, but only to communicate with a licensed public mobile telecommunications base transceiver station (a 'pico cell' such as those used in large buildings) onboard the aircraft with connection to telecommunications satellites. A control unit blocks onboard devices from terrestrial signals. Under these conditions the mobile devices in the aircraft operate at very low power. So, the class licence authorises persons to use mobile communication devices in aircraft if they are in an airliner equipped with a 'pico cell' unit (and operating under a public telecommunications service licence). The class licence does not authorise the use of any other form of mobile communication device in any airborne aircraft at any altitude. However, in an emergency safety has priority so airborne pilots might contact the ATC centres by mobile 'phone. The telephone numbers of the state ATC centres and the SAR hotline (1800 215 257) are given in ERSA GEN-FIS 'Use of mobile 'phones in aircraft' — store the numbers in your 'phone. For recommended actions during and following an emergency please read all of the ERSA Emergency Procedures Section ERSA EMERG; particularly the 'Activation of ELT' and the survival sub-sections. 5.5.2 Distress beacons and AusSAR ELTs, EPIRBs and PLBs In a life-threatening situation the pilot may activate a radio distress beacon when approaching, or on, the surface. The signal from the beacon will be detected by the specialised search and rescue system — Sarsat (Search And Rescue Satellite Aided Tracking system) and the Russian Cospas. The satellite-mounted Cospas-Sarsat receivers monitor only the global distress frequency, 406.025 MHz and are reputed to have been involved in more than 7000 rescues since the system was introduced in 1982. Analogue transmissions might also be picked up by nearby aircraft — regular passenger transport aircraft usually continually monitor the 121.5 MHz frequency and military aircraft monitor 243.0 MHz. In the Australian aviation regulatory environment, the generic name for distress beacons is Emergency Locator Transmitters [ELTs]. ELTs are usually a fixed installation within larger aircraft, but may be demountable. When armed, ELTs are designed to be activated automatically (perhaps by a g-switch) under a high-impact deceleration; or they can be manually activated by the pilot. (Unfortunately ELTs may not survive a high impact landing or the antenna may be disconnected in a lesser accident.) Similarly, the generic name for 406.025 MHz maritime environment beacons is Emergency Position Indicating Radio Beacons [EPIRBs]. The significant difference between EPIRBs and ELTs is that the former are buoyant and work at their best when floating freely and upright, while the ELTs work best on land — though they should be waterproof. The most expensive EPIRB is the 'float free' or 'float-to-the-surface', automatically activated maritime only type. Smaller, lanyard-equipped, manually operated, category 2 EPIRBs are designed to be placed in the water and allowed to float upright. Personal Locator Beacons [PLBs] were originally designed for personal use by ground travellers in a rugged environment or by those recreational sailors who don't venture very far out to sea — they probably float but perhaps not upright. The manually activated, pocket-sized, analogue PLBs were extensively used by recreational pilots — among many other users. In the Australian aviation scene PLBs and manually activated EPIRBs are classified as portable ELTs so, for aviation regulatory purposes, the ELT term encompasses fixed-installation ELTs and portable ELTs; the latter being the digital PLBs and the manually activated digital EPIRBs. Recreational aviation pilots carry PLBs or, if undertaking significant water crossings, should carry the personal EPIRBs that can be attached to a lifejacket or to clothing. (The term ELB [Electronic Locator Beacon] is sometimes used but this term is no longer defined in aviation regulations or by the Australian Maritime Safety Authority — which has search and rescue responsibility in the Australian region — so the term has no valid usage and adds to the confusion between aviation and AMSA definitions. ELBs were once in use as a 121.5 MHz beacon but their transmission format was not satellite-compatible and production ceased in the early '90s.) The now superseded analogue versions of PLBs/personal EPIRBs transmitted on the 121.5 MHz voice frequency and simultaneously on 243.0 MHz, but not 406.025 MHz. For aural recognition and homing that continuous wave transmission is modulated with a swept tone sounding like a two-tone siren and audible via a VHF transceiver. The 121.5 or 243.0 MHz transmission is used as a short range homing signal by search aircraft or surface vehicles. On 1 February 2010 the class licence for the 121.5/243.0 MHz distress beacons was finally withdrawn by the Australian Communications and Media Authority [ACMA], consequently it is now illegal to use those beacons for any purpose. On land there might be a requirement that PLBs/EPIRBs, when activated, must be placed in the centre of a ground mat formed from a sheet of aluminium kitchen foil, about 120 cm square — which provides the 56 cm radius ground plane. Read 'Activation of ELT' within the emergency procedures section of ERSA. Remember the requirement (AIP GEN 3.6 para 8.2) that pilots should monitor 121.5 MHz before engine-start and after engine-shutdown, to check for the 'two-tone siren' distress transmissions — and to ensure that your own beacon is not activated inadvertently. Distress beacons have been used in Australian aviation for at least 45 years and are an essential item for pilots who fly in sparsely populated areas, and for vehicle drivers who operate in remote areas. The buyer of a distress beacon should be well aware of how to keep it secure and to use it correctly, effectively, and only when in a life-threatening situation; also how to finally dispose of it without possibly causing costly problems to AusSAR. For beacon disposal instructions see beacons.amsa.gov.au/batteries-disposal.html. The 406.025 MHz ELTs On 1 February 2009, the Cospas-Sarsat satellites ceased processing distress signals on 121.5 MHz and now only process signals from the 406.025 MHz digitally-encoded PLBs, ELTs or EPIRBs. So, search (and rescue) for persons using the 121.5 MHz only units is totally dependent on time-consuming, expensive and difficult — and possibly dangerous — air and ground searches. The digitally-encoded PLBs, ELTs and EPIRBs that operate on 406.025 MHz, quickly provide position accuracy to within 5 kilometres or so using satellite trilateration. If the beacon has an integrated GPS input the location coordinate data are transmitted to the satellite, pinpointing the site to within 100 metres or less. This makes redundant the search portion of the rescue operation and greatly aids rapid recovery; and rapid recovery is vital when the aircraft occupants are injured or in difficult circumstances. The 406.025 MHz beacons generally also transmit a low power analogue 121.5 MHz final stage aircraft homing signal; for example, the Australian MT410G PLB at left. When activated the 406.025 MHz beacons send a 0.4-second data packet every 50 seconds. The packet includes a 15 hexadecimal character beacon identity code plus the country/SAR authority code within a 30 hexadecimal character distress message. That message is retransmitted by the satellite to the two AMSA ground stations. The hexadecimal identity code, marked on the unit as purchased, must be known to AusSAR's database, and linked to your personal and aircraft details. Part of the functional working of the 406.025 MHz beacon search and rescue system is having the owner of the beacon register it with the Australian Maritime Safety Authority [AMSA]. Requirement to register and carry 406.025 MHz beacons The requirement for an Australian aircraft to carry an approved distress beacon or emergency locator transmitter is stated in CAR 252A (as amended 1 February 2009). Every two-place recreational aircraft operating beyond 50 nm from their departure point is required to carry a 406 MHz beacon registered with AMSA. Single-place aircraft are amongst those exempted in CAR252A, so carriage of a beacon is not mandatory for CAO 95.10 aircraft — but it is certainly wise to do so. So, recreational pilots should acquire a 406 MHz beacon with internal GPS input (for example, the MT410G costs about $650) and register that beacon. In order to make the process of registration and upkeep of details easier, AMSA have an online registration program. This system is available to all beacon owners to use and there is no charge for its use; go to beacons.amsa.gov.au to register your unit and to find more details regarding how to purchase PLBs. AMSA will provide a registration sticker to be placed on the unit, the stickers provide owners and Flight Operations Inspectors with proof of current registration. The ELT registration must be renewed every two years and a new sticker attached to the device; see 'Renewing your registration'. Note: if a beacon has been activated inadvertently, switch it off and notify the Rescue Coordination Centre Australia by calling 1800 641 792 to ensure a search and rescue operation is not commenced. There is no penalty for inadvertent activations. According to their website — 'since its inception in 1982 the Cospas-Sarsat System has provided distress alert information which has assisted in the rescue of 26,779 persons in 7,268 distress situations [land, sea and air]. In 2008 only, the System provided information which was used to rescue 1,981 persons in 502 distress situations. The locations of these events are depicted on the map below.' For further general information, the next page in this guide is a document Aviation Distress Beacons written some time ago by David McBrien of AusSAR. Personal flight tracking systems There are several flight tracking systems available which allow interested parties to follow the progress of a flight via the internet. For example, Spidertracks is a system developed in New Zealand that uses a small (12×6×3 cm) demountable transceiver in the aircraft (with its own GPS engine) to send location, heading, speed, altitude reports at nominated time intervals — via the Iridium satellite global communications network — to a host computer, which users can access via the internet. The display includes flight track, reporting times and locations overlaid on a Google Earth map. There is a facility available which will activate email or text notification — to a user-nominated person or group of persons — if three contiguous reports are missed. Cost may be a problem. Australian Search and Rescue (AusSAR) If a registered civil aircraft issues a MAYDAY call, or is seen to crash away from a controlled aerodrome or is reported missing, Australian Search and Rescue has national responsibility for coordinating the search and rescue. In addition, AusSAR monitors satellite-intercepted signals via two ground stations in Australia and one in New Zealand. AusSAR is responsible for delivering search and rescue coordination in response to an activated distress beacon within AusSAR's area of responsibility — which covers all the Earth's surface between 75° East and 163° East and roughly 10° South to 90° South. Further information is contained in the document Understanding SAR services. 5.5.3 Aircraft radar beacon transponders Mode A/C transponders Transponders are specialised radio devices that form the airborne part of the Air Traffic Control Radar Beacon System [ATCRBS "at-crabs"]. Transponders respond to a 1030 MHz interrogation pulse, from an air traffic control secondary surveillance radar [SSR], by returning a high-energy 1090 MHz pulse that strengthens the radar return signal. Lower power primary surveillance radar [PSR] exists only within about 50 nm of the major civilian and military airports but such radars don't interrogate airborne transponders. SSR range is at least 100 nm from the radar unit, depending on target height. The surveillance (i.e. computer-aided search and track) radars provide only bearing and distance from the radar site, target height is provided by the airborne transponder. In addition, the response from transponders fitted to smaller civilian aircraft normally consists of a 12-bit ATC assigned identity/status code plus a 12-bit altitude reading (in units of 100 feet) which appear on the controller's SSR screen with the aircraft 'paint'. Civilian units with this identity (Mode A) plus altitude encoding (Mode C) interrogation response capability are known as Mode A/C transponders, sometimes they are referred to as 'Mode 3A/C'; the '3' just refers to a US military classification. The transponders receive the Mode C altitude data from altitude encoding devices. The 12-bit Mode A identity code is separated into four three-bit numerals using octal rather than decimal notation. Thus each numeral will be in the range 0–7; i.e. the numerals 8 and 9 will not appear in any identity/status code. The standard four-digit non-discrete identity code 'squawked*' by VFR aircraft is '1200' (all non-discrete codes end in '00') until radio contact with Air Traffic Services, who might then instruct the pilot to squawk a particular discrete (i.e. individual) code; e.g. 4367. The maximum number of discrete identity codes available for assignment at any one time is about 4000 (in decimal notation). *(Note: the 'squawk' term originated in Britain early in the second World War when the Chain Home early warning radar network was used for the first ground controlled fighter interception system against incoming air raids. The RAF fighters were equipped with a rudimentary 'identification friend or foe' (IFF) transponder, code-named 'Parrot'. When the ground controller required a flight or squadron to switch on their transponders the instruction was "Squawk your parrot". Conversely, "Strangle your parrot" to switch off.) Mode A/C transponders have a very important 'identify' [IDENT] or 'special position identification' [SPI] facility which, when operated, momentarily adds an additional bit to the '1200' non-discrete identity code, or whatever discrete code is being used by the pilot. That causes the aircraft's 'paint' to brighten or change colour on the controller's display. So, for example, when the controller wishes to locate a particular aircraft on the display screen, among all those currently squawking '1200', the controller will request the pilot to "squawk ident"; i.e. operate the 'ident' button, knob or spring-loaded toggle switch. Pilots must not squawk 'IDENT' unless told to do so by ATC or when first squawking an emergency code. The non-discrete transponder squawk codes (for emergency use only) are: 7700 emergency 7600 VHF communications failure 7500 unlawful interference (i.e. hijacking). See transponder emergency procedure below. Mode S transponders The Mode A/C radar surveillance system is rather limited. The Mode S transponders, carried by regular passenger transport aircraft, use their National Airworthiness Authority [CASA for Australian aircraft] assigned permanent 'ICAO 24-bit Aircraft Address'. The 24 binary digits allow a total of 16.8 million individual addresses; thus every aircraft can be permanently assigned a unique address, generally based on the aircraft's country of registration and issued by their National Airworthiness Authority. Consequently, those aircraft can be selectively addressed by ground stations or other aircraft for transfer of information as digital data. This message format is called Mode S (for 'selective address') but the transponders also have the normal Mode A/C functions. *Note: Binary, octal, decimal and hexadecimal numerical notation. Our everyday decimal numbering system has a base of ten with 10 markers 0–9. Octal and hexadecimal notation refer to versions of computer numerical display that assist human perception of the binary digit representation used in computers. Binary numbering is base-2 with two states (on or off) per binary digit (bit) representing 0 and 1. Octal notation is base-8 with eight markers 0–7 and uses one group of three bits to represent any of the eight numerals 0–7. The hexadecimal (or hex) numbering system is base-16 with 16 markers 0–9 plus A–F, the latter representing the decimal numerics 10 through 15. A decimal number of '255' is represented by the hex number 'FF'. Hexadecimal uses one group of four bits to represent any of the sixteen numerals 0–15 rather than the 8-bit byte normally used for alphanumeric coding. For Australian aircraft the ICAO 24-bit Aircraft Address code, also known as the 'Mode S Transponder Code is usually stated in 6-digit hexadecimal notation format. All Australian civil aircraft with a Mode S transponder installed are required to have a registered permanent ICAO 24-bit Aircraft Address assigned; this is accomplished by emailing CASA at [email protected] who will assign a permanent ICAO 24-bit Aircraft Address code for that aircraft in the range '7C0000' to '7F0000'. For RA-Aus registered aircraft the code may be entered into a Mode S transponder by the aircraft owner; for aircraft with national registration (i.e. VH) the code must be entered into a Mode S transponder by an appropriately trained and rated licensed aircraft maintenance engineer (LAME), or CASA authorised person, at the time of transponder installation and re-tested at 2-year intervals. Note: only the CASA assigned aircraft address should be entered into the 24-bit hexadecimal field otherwise there is the possibility of duplication of aircraft addresses. If a CASA-assigned aircraft address has not been entered and verified in a Mode S transponder then the unit may only be operated in A/C mode. Also, as with the Mode A/C transponders, the Mode S transponders have an identification function that may be known as 'Aircraft Identification', 'Flight Identification' or 'FLIGHTID'. This Aircraft Identification may be no more than seven alphanumeric characters but, for RA-Aus registered aircraft, CASA require the Aircraft Identification to be five alphanumeric characters consisting of the four numeric digits of the aircraft's registration mark preceded by the letter 'R' (for RA-Aus) without hyphens or included spaces, e.g. Jabiru 24-7147's identification is 'R7147'. For RA-Aus aircraft the Aircraft Identification is a permanent code, for other aircraft it may be entered/changed by the pilot as required. In Australia, prior to 2010, there was no Mode S secondary surveillance radar network so the main Mode S transponder function was to allow aircraft equipped with Traffic Alert and Collision Avoidance Systems [TCAS] to communicate directly with each other, thereby enabling mutual resolution of potential traffic conflicts. The transponders – in combination with a GNSS receiver – periodically 'squitter' a burst of data containing tracking information such as the aircraft's position, altitude, vector and velocity. (Squitter means a rapid R/F emission.) Such transponders also act as the aircraft's digital modem terminal for data upload/download and distribution. Mode S can also provide faster, more accurate ATC surveillance, provided the ground SSRs are of the fast, single-pulse interrogation Mode S type. The non-Mode S Australian SSRs are now in the process of replacement, both in the main city hubs and en route. When interrogated by a Mode S SSR a Mode S transponder replies with its Flight Identification plus its ICAO Aircraft Address, plus other relevant data. From February 2014 an aircraft that is newly registered (or that is modified by having its transponder installation replaced) and that is operated in Class A, B, C or E airspace, or above 10 000 feet amsl in Class G airspace, must carry a serviceable Mode S transponder, but that Mode S transponder is not required to have the 'extended squitter' hardware and software (known as '1090ES') to transmit Automatic Dependent Surveillance–Broadcast [ADS-B] data. The term 'extended squitter' refers to an additional [112-bit] ADS-B data packet, which is part of the enhanced Mode S transponder data link standards for ADS-B. The 1090ES satellite-based surveillance and traffic management system is currently implemented for Australian airspace above 29 000 feet. See the Australian ADS-B implementation program. TCAS The Traffic Alert and Collision Avoidance Systems [TCAS II], fitted to all Australian RPT aircraft exceeding 30-passenger capability, also send out Mode C interrogation pulses in the same manner as an SSR, and use the interrogation responses broadcast from aircraft Mode A/C transponders (within a range of 14 nm) to determine collision risk. (TCAS computers determine the velocity vector of an aircraft within range — ascertaining distance by the response time, bearing by a directional antenna and altitude from the 12-bit reading encoded in the response.) If there is no altitude given then the computer can only provide a traffic alert rather than a 'resolution advisory' recommending a particular action to the pilot. TCAS II won't detect an aircraft fitted with an operating Mode A-only transponder. TCAS systems also utilise their Mode S-capable transponders to transfer data between aircraft TCAS systems for mutual resolution of traffic conflicts, or to provide a data upload/download link with a ground station. For a description of TCAS read the article 'Collision Avoidance' in the April 1999 issue of the Australian Civil Aviation Safety Authority's Flight Safety Australia magazine. Transponder operating regulations For traffic separation purposes all aircraft — including recreational aircraft — operating in Class A, C and E Australian airspace, or in any airspace above 10 000 feet, must be fitted with an operating Mode A/C transponder. If an aircraft is transponder-equipped the unit must be operated constantly, whether in controlled or non-controlled airspace. There are some exemptions in Class E if the aircraft's electrical system is not capable of continuously powering a transponder. No aircraft may operate in Class E within 40 nm of a Class D tower without a functioning transponder. For further information see controlled airspace. A recreational aircraft operating in Class E should check with Air Traffic Control to confirm that the transponder is functioning correctly. Normal operating procedure: 1. After engine-start turn the transponder mode switch from 'OFF' to 'STBY' (standby) to warm up the unit — which may take a couple of minutes. When the transponder is in 'STBY' it will not respond to an SSR interrogation. Set the identity code '1200' unless advised otherwise by ATC. 2. Before take-off turn the mode switch to 'ALT' (altitude) rather than the 'ON' position. Unless ATC instructs you to do so there is really no need ever to use the 'ON' position. The 'ON' position directs the transponder to respond only to a Mode A interrogation. When 'ALT' is selected, even if there is no altitude encoder fitted, the transponder will still return a response pulse to a Mode C interrogation coming from a ground radar or from a TCAS aircraft, but without any altitude data of course. Leave the switch in the 'ALT' position until turning off the runway at the destination, unless the identity code is to be changed during flight; in which case place the unit in 'STBY' mode while the change is being effected. 3. For further information on operation of transponders see AIP ENR 1.6 subsection 7. A user's manual for the Australian Microair T2000 transponder may be downloaded from the Microair website. Transponder emergency procedure For any transponder-equipped aircraft within radar coverage — say, up to 100 nm from the SSR site for lower altitudes — and whether outside (or underneath) controlled airspace, the ATC radar emergency service will provide navigation assistance if the aircraft is in distress or experiencing navigational difficulties. In an emergency situation the pilot should select the emergency status code 7700, operate the 'IDENT' function and, if possible, contact the service on the overlying en-route area control frequency shown on the ERC-L, call-sign CENTRE; e.g. BRISBANE CENTRE. PAN-PAN PAN-PAN PAN-PAN BRISBANE CENTRE THRUSTER ZERO TWO EIGHT SIX / ZERO TWO EIGHT SIX / ZERO TWO EIGHT SIX EXPERIENCING NAVIGATION DIFFICULTIES IN DETERIORATING VISIBILITY REQUEST POSITION [or NAVIGATION] ADVISORY SQUAWKING 7700 Deviation into an active restricted zone Should an aircraft be forced to deviate into an active restricted zone due to the weather — without an ATC clearance — then the pilot must declare a PAN-PAN, squawk 7700 and broadcast on 121.5 MHz and on the appropriate ATC frequency. ATC will declare an 'Alert Phase'. The declaration of an emergency will not guarantee safe passage in a hazardous restricted zone. Mode C transponder maintenance RA-Aus aircraft owners should note that transponders with an active altitude reporting facility (altitude encoding altimeter or a blind encoder) must be maintained in accordance with CASA regulations not RA-Aus regulations. CAO 100.5 appendix 1 requires that the system is tested by a CASA-licensed maintenance engineer at intervals not exceeding 24 months or after any change/modification to the altitude reporting system component(s) or interwiring. Code 2100 is used by maintenance personnel for testing purposes. 5.5.4 Can it ever be appropriate to monitor 121.5 MHz en route? The following was written by Boyd Munro of Air Safety Australia 121.5 is the International Distress Frequency. A recent survey by Air Safety Australia has revealed that few Australian pilots monitor 121.5, apart from those who work or have worked for an airline, and those with significant overseas experience. I got a big surprise from this, because I always monitor 121.5 en route without even stopping to think why. It’s just something I do, like getting dressed before I leave the house in the morning. Remember that “monitor” in this context means “listen without talking”. The survey also showed that the term “monitor” is quite widely misunderstood. For the most part we Australian pilots are not trained to monitor 121.5 when flying en route, but there are powerful reasons why we should. 1. We are instantly available to another pilot who experiences an emergency in the air, or crashes but still has a working radio and calls on the International Distress Frequency. This is not merely good airmanship, it is responsible citizenship. 2. We can pick up ELT signals, so if another pilot crashes we can bring help to him. ELT signals are also picked up by satellites [this capability ceased 1 February 2009 ... JB] but hours can elapse before one of those satellites passes over the accident site, and if the ELT’s antenna was damaged in the crash the high-flying satellite may not be able to pick up the signal at all. Airmanship/citizenship again. 3. We can be contacted at any time. For example “Aircraft at position X, you are entering restricted area R123 and will be intercepted unless you make a 180 turn and leave the area forthwith.” 4. All airlines monitor 121.5 en route. 5. ICAO requires that all aircraft monitor 121.5 at all times in areas where ELTs must be carried (which includes the whole of Australia). 6. ICAO recommends that all aircraft monitor 121.5 at all times to the extent possible. 7. If you crash and survive but are injured, 121.5 is, overall, the best frequency to use to summon assistance. A call on 121.5 is almost always answered anywhere in the world except in the polar regions. That’s because of the large number of good airmen and good citizens who monitor 121.5 when flying en route. 8. An intercepting aircraft is required by ICAO Annex 2 to call us on 121.5 before shooting us down. Until 27th November 2003, the Australian recommendation (it was never a requirement) was that we should monitor the “Area Frequency” whilst en route VFR. The Australian recommendation now is that we monitor an appropriate frequency. One practical benefit of monitoring 121.5 as opposed to the old “Area Frequency” is that 121.5 is almost silent. The only transmissions ever heard on 121.5 are those relating to distress or an aircraft which ATC has “lost” or transmissions made unintentionally (when the pilot intended to transmit on a different frequency). There is not the noise and distraction that occurs on an area frequency, leaving the pilot better able to fly the aircraft and maintain a good lookout. Air Safety Australia urges all members to become familiar with monitoring 121.5 when flying en route, and then to always consider 121.5 when choosing which frequency to monitor when flying en route. When you monitor 121.5 for the first time, remember that it is a silent frequency. Don’t make any transmissions on it unless you experience an emergency or you are responding to another aircraft which is experiencing an emergency and has transmitted on 121.5 Boyd Munro, 19th March 2004 STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

5.4.1 Communications in the vicinity of airfields in Class G airspace Common traffic advisory frequencies If a public-use non-controlled* aerodrome has a reasonable number of daily movements Airservices Australia assigns a discrete VHF frequency to that site, which all aircraft should (not must, see AIP ENR 1.1 para 21.1.14.1) monitor when operating in the vicinity of that airfield. This discrete frequency is known as the common traffic advisory frequency or CTAF (see-taff) and is shown in the ERSA entry for that location and is also depicted on the VNC, VTC and ERC-L aeronautical charts – next to the airfield ID as 'CTAF frequency'; e.g. 'CTAF 118.6'. However, if an airfield or a private airstrip is depicted on the VNC, VTC, ERC-L or WAC aeronautical charts, without a discrete CTAF being shown, then the default 'Multicom' frequency of 126.7 MHz should be used. The larger 'broadcast areas' are defined airspace volumes in Class G airspace for which a discrete CTAF has been allocated. (That discrete CTAF could be 126.7 MHz.) All operations, including those at aerodromes (charted or uncharted) and any landing ground, within this area shall use that CTAF as the broadcast frequency. See AIP Book ENR 1.4 section 3.2. Broadcast area lateral boundaries are shown on the aeronautical charts with a note stating "For operations in this area SFC – (altitude) use CTAF (frequency)". The area around the Avalon, Vic control zone is an example. The lateral and vertical limits are defined on the charts; the default vertical limit is 5000 feet amsl. In all other cases the flight information area frequency should be used at non-controlled aerodromes or landing grounds. *Note: the Civil Aviation Regulations define and use the term 'non-controlled aerodrome', however Airservices Australia's AIP book has been erroneously using the USA term 'non-towered aerodrome' for some time (the term is or was also used in some advisory publications) but, as the 'non-towered aerodrome' term is not yet supported by legislation, all references were deleted from AIP or replaced by 'non-controlled aerodrome' effective 21 August 2014. CARs 166, 166A, 166B, 166C, 166D and 166E establish the regulatory environment for operations at non-controlled aerodromes. If an aerodrome air traffic control tower does not maintain a 24-hour 7-day service CAR 166D allows CASA to classify any of those aerodromes as a designated non-controlled aerodrome during the periods when the control tower is unmanned. The 'designated' term prescribes mandatory carriage and use of radio on the airfield frequency. CAR 166C defines the responsibilities and mandatory actions for broadcasting on VHF radio when operating in the vicinity of a non-controlled aerodrome. When planning a flight into an airfield not listed in ERSA, it is advisable to check the frequency being used with the airfield owner/operator — there are unlisted landing areas where a dedicated airfield frequency, other than the multicom 126.7 MHz, may still exist but is not shown on the aeronautical charts; see specific frequencies. This particularly applies to airfields supporting glider operations. CTAFs are usually not monitored by Air Traffic Services. An aircraft is 'in the vicinity' of a non-controlled aerodrome if it is within a horizontal distance of 10 nautical miles from that aerodrome and at a height above the aerodrome that could result in conflict with operations at the aerodrome. The height dimension of the aerodrome's airspace is a rather nebulous concept — few light aircraft pilots would be familiar with the potential flight path profiles of fast-moving RPT aircraft conducting their normal 'straight-in' or 'circling' approaches or their climb-out; so the upper and lower 'vicinity' limits (at various distances from the airfield with allowance for terrain elevation) are difficult to judge. Perhaps 5000 feet amsl could be regarded as the height limit of the airspace at most CTAF aerodromes – but aerodrome elevation must be taken into account. The 10 nm radius of the 'vicinity' encloses more than 1000 square kilometres of territory which is likely to contain other airfields, private airstrips (and paddocks) used for recreational operations and agricultural work, any of which may, or may not, appear in ERSA or other airfield guides. When aerodromes are in close proximity they are usually allocated the same CTAF, but that is not always so and only the pilot can judge the best time to make the appropriate frequency changes when operating in the vicinity of more than one landing area. CAR 166E requires that, if the aerodrome listing shown in ERSA FAC describes the airfield as 'CERT' or 'REG' or 'MIL' or is a 'designated non-controlled aerodrome'*, then the carriage and use of VHF radio — confirmed to be functioning on the designated frequency — is mandatory for all aircraft operating in the vicinity and, of course, the pilot of an RA-Aus aircraft must hold a RA-Aus radio operator endorsement. There are about 300 such civilian certified or registered airfields in Australia, all of which usually have scheduled regional RPT movements. I have compiled a listing in text file format of those CASR Part 139 certified aerodromes [184] and registered aerodromes [120] but it will not reflect current status, so check ERSA. Carriage of VHF radio is usually not mandatory within the vicinity of the other non-controlled airfields — unless a temporary notam is current — though highly recommended. But all radio-equipped (hand-held or fixed installation) aircraft must maintain a listening watch and must be prepared to broadcast on the CTAF or the Multicom frequency 126.7 MHz. *Note: prior to about 2006 'designated non-controlled aerodromes' were commonly known as 'CTAF(R)s'; in the 1990s they were 'MBZs' – mandatory broadcast zones. CASA have produced two advisory publications to support CTAF procedures and provide guidance on a code of conduct to allow greater flexibility for pilots when flying at, or in the vicinity of, non-controlled aerodromes. These Civil Aviation Advisory Publications (available on this website) are: CAAP 166-1 'Operations in the vicinity of non-controlled aerodromes' (August 2014) and CAAP 166-2 'Pilots responsibility for collision avoidance in the vicinity of non-controlled aerodromes using 'see and avoid' (December 2013). Note that the 'ultralight' term as used in the CAAPs when recommending a 500 feet circuit height, refers only to those minimum aircraft which have a normal cruising speed below 55 knots, or thereabouts. CASA has produced an online interactive learning tool titled 'Operations at, or in the vicinity of, non-towered (i.e. non-controlled) aerodromes' which is now available at CASA online learning. About 100 Australian aerodromes are equipped with an Aerodrome Frequency Response Unit [AFRU] or 'bleepback' — a device that transmits an automatic aural response when a pilot transmits on the CTAF, thus confirming that the pilot is on the correct airfield frequency. AFRU features are explained in AIP GEN 3.4 sub-section 3.4. Accessing AIP Book and ERSA Airservices Australia publishes online versions of the AIP Book, SUPS, AICs and ERSA at www.airservicesaustralia.com/publications/aip.asp (click the 'I agree' button to gain entry). To find a particular section of AIP or ERSA you have to click through a number of index pages. The section/subsection/paragraph numbering system was designed for a readily amendable looseleaf print document, so you may find it a little confusing as an online document. Unicom services Any Unicom (universal communications) service that exists would be a private non-ATS aeronautical station licensed by ACMA that may provide — on pilot request — basic wind, weather and perhaps some traffic advisory information in plain language, but certainly not a traffic separation service. Unicom may be provided by the aerodrome operator, the local refueller or an airline representative during RPT operational periods. Any Unicom facility and call-sign would be indicated in ERSA. Refer to AIP GEN 3.4 sub-section 3.3. The advantage of Unicom to recreational pilots may be that the service (if it operates on the CTAF) provides some additional information and thereby confirmation of the correct frequency selection and operation of the radio. Unicom communications always take second place to pilot-to-pilot communications on the CTAF. Certified air/ground radio services [CA/GRS] In 2011 there remained just one non-towered aerodrome operator (Ayers Rock) providing a 'certified' ground-to-air radio information service on the CTAF to all aircraft operating in the vicinity. This service is usually provided where, and when, there is significant RPT traffic. They are not an Airservices Australia sponsored service but the radio operators 'have been certified to meet a CASA standard of communication technique and aviation knowledge appropriate to the services being provided.' For recreational aviation the service is similar to a Unicom service but the CA/GRS operator will most likely provide better traffic information. For more details read AIP GEN 3.4 section 3.2. Operating times, call signs and any special procedures will be shown in the aerodrome ERSA entry. 5.4.2 Radio procedures at non-controlled airfields Communication requirements when operating in the vicinity of a non-controlled aerodrome are defined in AIP Book ENR 1.1 section 21 table 'Summary of broadcasts - all aircraft at non-controlled aerodromes'. The following seven broadcasts are 'recommended', meaning that the operational decisions regarding their use are then properly left to the pilot. The pilot is expected to conduct operations in an airmanlike manner in accordance with the existing environment and traffic conditions. There may be requirements detailed in the ERSA entry for a particular airfield that vary from the standards detailed below. Some temporary variation in the following procedures may also be stipulated, via NOTAM or AIP supplement, for special events; e.g. the annual Birdsville Race meeting or the RA-Aus Easter weekend national fly-in at Temora. Arrival and transit advisory broadcasts VFR aircraft reaching the vicinity of an aerodrome within Class G airspace, and intending to land, must monitor the designated airfield frequency (otherwise the multicom frequency) and should make these broadcasts on that frequency: an inbound broadcast — by 10 nautical miles from the airfield a joining circuit broadcast immediately before joining the circuit if making a straight-in approach, broadcast on final approach not less than 3 nm from the threshold if joining on base leg, broadcast joining base leg prior to joining on base. (Note: straight-in approaches and joining the circuit on the base leg, though acceptable, are not recommended procedures.) If intending to operate in the vicinity of an aerodrome, rather than land, the aircraft must monitor the appropriate frequency and broadcast: (a) if in transit, an overflying report — by 10 nm from the airfield. (b) if operating from a private airstrip less than 10 nm from the aerodrome, an intentions report once airborne. Regulations recommend a transit report if the flight path passes in the airfield vicinity at a height that 'could result in conflict with operations'. A high-performance aircraft departing from an airfield could attain 5000 feet agl before reaching the 10 nm boundary so caution would dictate a transit report advisable even if cruising altitude is above 5000 feet agl — and an airfield should not be overflown at any height less than 3000 feet agl. If you don't hear or see any other traffic in the area do not assume there is none and neglect to make any calls. Departure advisory broadcasts All aircraft operating from a non-towered aerodrome must monitor the airfield CTAF and should make the following broadcasts on that frequency: immediately before, or during, commencing taxiing to the runway, make a taxiing broadcast broadcast immediately before entering runway. Broadcasts within the circuit The AIP no longer defines any mandatory or recommended broadcasts such as 'turning downwind', 'turning base', 'turning final' or 'clear of runway'. Instead CAR 166C states: 'The pilot must make a broadcast ... whenever it is reasonably necessary to do so to avoid a collision, or the risk of a collision, with another aircraft ...' A turning final broadcast should be regarded as mandatory. It is often difficult to see a stationary aircraft, vehicle or even line marking operators on the runway, let alone an aircraft on a straight-in approach. Most mid-air collisions occur on approach where a faster aircraft descends upon the aircraft in front (see 'Further online reading') and collisions do occur on runways after landing. The turning final call does provide a warning at a time when the aircraft turning is most visible. The necessity for a turning base or other circuit call are matters of judgement that depend upon the amount and type of traffic, separation and flow. The more ordered it is the fewer the calls needed. On the other hand, if there are no other aircraft heard or seen in the circuit then there will be minimum chance of frequency interference or frequency congestion — and it will be safer — if every possible call is made. 5.4.3 Prescribed CTAF broadcast formats All VFR broadcasts from an aircraft station in Class G are quite simple, having much the same content presented in much the same sequence: The location Who I'm calling Who I am Where I am What my intentions are The location repeated Expressed in the official manner: Location (The general area, usually an airfield name) Called station/s ID (Who I'm calling) Calling station ID (Who I am; i.e. aircraft type and registration) Calling station position (Where I am, usually in reference to the airfield) Calling station intentions (What my intentions are) Location repeated For a broadcast transmission there is no specific station being called; you are just addressing all those aircraft stations (and possibly ground stations) in the vicinity who are maintaining a listening watch on the CTAF. The called station ID is usually "TRAFFIC" and presumably this is meant to include ground aeronautical stations and aeronautical mobile stations, rather than just aircraft stations. If you are making a broadcast call where you are asking a question and hope for a response then the called station ID would be "ANY STATION" or "ANY TRAFFIC" preceded by the location name. The calling station ID is the aircraft call-sign which, for RA-Aus aircraft, already includes the aircraft type. For a General Aviation aircraft the calling station ID is the three-letter aircraft registration, so the aircraft type must be added; e.g. PIPER WARRIOR/ALPHA YANKEE CHARLIE. In the following example broadcasts the location is 'TANGAMBALANGA' and the aircraft call-sign is 'THRUSTER ZERO TWO EIGHT SIX'. Taxiing call format The taxiing call notifies all aircraft that you are about to taxi to a runway, and particularly alerts any other ground traffic that is taxiing to or from a runway to be vigilant for traffic movements. [location] TRAFFIC CALL-SIGN TAXIING RUNWAY (number) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX TAXIING RUNWAY TWO FIVE TANGAMBALANGA Entering runway call format The 'entering runway' call alerts any traffic in the circuit or clearing the runway that you are about to use the runway for take-off. The call particularly alerts aircraft on base leg or straight-in approach to be prepared to go around in the event that there is a conflict. (Location) TRAFFIC CALL-SIGN ENTERING RUNWAY (number) (Intentions or the departure quadrant) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX ENTERING RUNWAY TWO FIVE (or ENTERING AND BACKTRACKING RUNWAY TWO FIVE) FOR CIRCUITS or DEPARTING TO THE SOUTH TANGAMBALANGA Aircraft should remain at the runway holding point until all checks are complete and the runway and the approach are seen to be clear — then make the ENTERING RUNWAY broadcast. If there has been a significant delay between the entering runway broadcast and commencement of take-off then a ROLLING call may be helpful to aircraft on the approach. The format would be the same as the entering runway call but with the word ENTERING replaced with ROLLING. If you decide to abandon the take-off after entering the runway then broadcast ABANDONING TAKE-OFF plus your intentions regarding vacating the runway. If you intend taxiing to an exit keep to the left of the runway — just in case! Inbound call format (Location) TRAFFIC CALL-SIGN (Position — reported as the distance and the compass quadrant from the aerodrome) (altitude) (Intentions) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX ONE TWO MILES NORTH-EAST / TWO THOUSAND FIVE HUNDRED INBOUND or INBOUND FOR A STRAIGHT-IN APPROACH RUNWAY TWO FIVE TANGAMBALANGA Straight-in approaches are acceptable but not recommended. If you intend to make a straight-in approach that intention should be included in the initial inbound broadcast. Some aircraft may report their position in terms of magnetic bearing from the airfield or the VOR radial. Such information is officially acceptable but the compass quadrant format is advisable, being readily understood by all and quite sufficient to alert other aircraft. Note that the word 'altitude' does not precede 2500; the figures are unlikely to be confused with anything else. Do not precede the altitude figures with the word 'AT' — which is reserved to specify time. When on descent the altitude might be expressed as 'DESCENDING THROUGH (altitude)'; e.g. 'ONE TWO MILES NORTH-EAST / DESCENDING THROUGH FOUR THOUSAND FIVE HUNDRED'. Also note that we have transmitted the location twice, which is always required as there may be several airfields within range on the same frequency, and doubling up the name helps to clarify the transmission. If the airfield name is short, or similar to another airfield within range (say 60 nm), then additional mention of the location may be appropriate; as in the following: BOURKE TRAFFIC THRUSTER ZERO TWO EIGHT SIX ONE THREE MILES NORTH-EAST BOURKE / TWO THOUSAND FIVE HUNDRED INBOUND BOURKE If your groundspeed is low and it will take some time to reach the circuit area it may be advisable to add your estimated time of arrival to the intentions. If so, it is conventional for the time to be expressed in minutes past the hour, in which case the previous call might be: 'INBOUND ESTIMATE BOURKE AT FOUR FIVE'. If you estimate your arrival will be near enough to the hour then the call would be 'INBOUND ESTIMATE BOURKE ON THE HOUR'. Don't forget aviation times are UTC so the minutes in local time do not coincide with the minutes in UTC when the time difference in the area includes a half-hour — Central (Australia) Standard Time, for example. In such instances it may be advisable to append the word 'ZULU' to the time in UTC minutes — or best use the local time and append the term 'LOCAL TIME' to the message; i.e. 'INBOUND ESTIMATE BOURKE ON THE HOUR LOCAL TIME'. Transit call format (Location) TRAFFIC CALL-SIGN (Position — reported as the distance and the compass quadrant from the aerodrome) (altitude) (Intentions) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX ONE TWO MILES SOUTH TANGAMBALANGA / MAINTAINING THREE THOUSAND FIVE HUNDRED OVERFLYING TO THE NORTH TANGAMBALANGA The broadcast indicates the intent to maintain 3500 feet while overflying the area on the way north. Joining circuit call format (Location) TRAFFIC CALL-SIGN JOINING (position in circuit – upwind, crosswind or downwind) (location) (runway) (Intentions) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX JOINING DOWNWIND RUNWAY ZERO SEVEN TANGAMBALANGA It is only necessary to state intentions if you are not intending to land and turn off the runway. If you are intending to do a few circuits first then the transmission is: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX JOINING CROSSWIND RUNWAY ZERO SEVEN FOR CIRCUITS (or 'FOR TOUCH-AND-GO' if you don't intend to turn off the runway) TANGAMBALANGA Final approach report format for straight-in approaches The 'final approach' call must be made at not less than 3 nm from the runway threshold. (Location) TRAFFIC CALL-SIGN FINAL APPROACH (runway) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX FINAL APPROACH RUNWAY ZERO SEVEN TANGAMBALANGA or TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX FINAL APPROACH RUNWAY ZERO SEVEN BACKTRACKING AFTER LANDING TANGAMBALANGA Clear of runway call format This call that you have turned off the runway particularly helps where a rise in the runway obscures the view of an aircraft preparing to take-off. (Location) TRAFFIC CALL-SIGN CLEAR OF RUNWAY (runway number) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX CLEAR OF RUNWAY ZERO SEVEN TANGAMBALANGA Turning downwind call format Although not mentioned in AIP the following 'in-circuit' broadcasts may be made if the circuit traffic situation warrants use of any of them. A 'turning downwind' call could be made when starting the turn onto the downwind leg — if the circuit was joined crosswind or if the aircraft is doing touch-and-goes. (Location) TRAFFIC CALL-SIGN TURNING DOWNWIND (runway) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX TURNING DOWNWIND RUNWAY ZERO SEVEN TANGAMBALANGA Turning base call format The 'turning base' call should be made when starting the turn onto base, as it provides a more precise location for sighting and a banked aircraft is more visible. (Location) TRAFFIC CALL-SIGN TURNING BASE (runway) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX TURNING BASE RUNWAY ZERO SEVEN TANGAMBALANGA If you are doing a right-hand circuit it is advisable to say so in the transmission, for example 'TURNING RIGHT BASE'. Turning final call format The 'turning final' call should be made when starting the turn onto final. (Location) TRAFFIC CALL-SIGN TURNING FINAL (runway)] (Intention) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX TURNING FINAL RUNWAY ZERO SEVEN TOUCH-AND-GO TANGAMBALANGA If you are doing circuits then you should add the intention 'TOUCH-AND-GO'; or if this is the last landing of a session of touch-and-go circuits then "FULL STOP' so that any following aircraft doing circuits-and-bumps can make the allowance for runway separation. Broadcast etiquette There are a few unwritten rules that greatly aid understanding by those maintaining a listening watch on the frequency: First ask yourself; "Is this call really necessary?" Mentally compose your message using aviation English (but no jargon), before operating the press-to-talk switch, thus avoiding a transmission containing 'umms' or 'aahs' or long pauses. Transmit once and transmit succinctly! Listen out for a second or two before transmitting so that you don't broadcast over someone else. Ensure you operate the press-to-talk switch before you start speaking; otherwise you are going to cut off the first word or part of it, probably making the broadcast useless to others. This is particularly so because the first word of the transmission is required to be the location. Speak distinctly and at a normal level (speaking loudly will distort the transmission) and at a normal pace (no-one appreciates a clipped, rapid-fire broadcast from the would-be 'hot-shot' pilot); and don't run the words together. Usually the microphone is designed to be squarely in front of the lips and 1–3 cm from them. Ensure the transmission system is of reasonable quality, properly maintained and operated in accordance with the manual. Avoid using superfluous words like 'IS taxiing', 'IS entering' or 'TRACKING for Holbrook' or 'PLEASE' or 'THANKS'. The term 'tracking' is usually only associated with a VOR radial or magnetic track; e.g. TRACKING ZERO TWO ZERO. Don't use non-aviation English phrasing such as '(call-sign) TURNS base' instead of '(call-sign) TURNING base'. Such phrasing is confusing — particularly to students — and may grate on other listeners; consequently the listener may not absorb the information and the broadcast has no value. Avoid confusion and annoyance! Ensure you are not inadvertently transmitting because of a stuck microphone switch. It is very annoying to others, possibly adding to stress and detracts from airfield safety. It can be extremely embarrassing to yourself, and perhaps costly, if you happen to be transmitting the cockpit conversation. Listen carefully to any message being transmitted so that you fully understand it. If you don't understand a transmission ask for a repeat — AIRCRAFT CALLING SAY AGAIN. And remember your own transmission must not include: profane or obscene language deceptive or false information improper use of another call-sign. And do not attempt to avoid landing fees by sneaking in without using the radio. Such actions are stupid but may be criminally reckless. 5.4.4 Discretionary broadcast formats Although radio calls should be kept to a minimum, there are times when traffic circumstances indicate some extra or discretionary calls would be helpful to all in maintaining safe separation; or when you do something unusual such as a go-around or back-tracking after landing. Discretionary calls may be shorter than standard calls. Going around call format If it is necessary to abort the landing and conduct a go-around, a broadcast may be helpful to others. (location) TRAFFIC CALL-SIGN GOING AROUND (runway number) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX GOING AROUND / RUNWAY ZERO SEVEN TANGAMBALANGA If the go-around was necessitated by something that may affect other aircraft then add information to the broadcast; e.g. GOING AROUND / RUNWAY ZERO SEVEN OBSTRUCTED BY LIVESTOCK Departure call format If, for example, you had been practising touch-and-goes and are now leaving the circuit it may be helpful to other aircraft to inform them of your intentions to depart the circuit. [location] TRAFFIC CALL-SIGN DEPARTING (runway) (turn) (departure quadrant) Location repeated For example: TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX DEPARTING FOR HOLBROOK TANGAMBALANGA There is a possibility that the word 'TO' might, in some circumstances, be confused with the numeral 'TWO' — or the word 'FOR' be confused with the numeral 'FOUR' — so some care is needed when composing a transmission. Requesting information There are occasions when a request for information from other aircraft is appropriate. For example, when approaching an airfield and no traffic has been heard on the airfield frequency but you would like to know what runway is in use — possibly by non-radio aircraft. In this case use the call ANY STATION (location) thus: ANY STATION TANGAMBALANGA THRUSTER ZERO TWO EIGHT SIX REQUEST RUNWAY IN USE TANGAMBALANGA The response from a general aviation aircraft on the ground or in the circuit might be: THRUSTER ZERO TWO EIGHT SIX ALPHA YANKEE CHARLIE TANGAMBALANGA RUNWAY ZERO SEVEN IN USE And the acknowledgment: RUNWAY ZERO SEVEN THRUSTER ZERO TWO EIGHT SIX 5.4.5 Communicating with Unicom or CA/GRS stations When inbound to an airfield with a Unicom or CA/GRS service, an information request might take this form (the Unicom call-sign is generally the location plus 'UNICOM'; the CA/GRS call sign will be location plus 'RADIO'): TANGAMBALANGA UNICOM THRUSTER ZERO TWO EIGHT SIX ONE FIVE MILES SOUTH-EAST INBOUND FOR LANDING REQUEST WIND AND TRAFFIC INFORMATION TANGAMBALANGA The informal response from the ground operator might be: "THRUSTER ZERO TWO EIGHT SIX — TANGAMBALANGA UNICOM — WIND IS ZERO SIX ZERO AT TEN KNOTS — A WARRIOR IS DOING CIRCUITS AND A DASH EIGHT INBOUND FOR A STRAIGHT-IN APPROACH ON ZERO SEVEN" There is no requirement to read back any of the information communicated but without a reply the ground operator is left wondering, so the acknowledgment: ROGER THRUSTER ZERO TWO EIGHT SIX Before taxiing at an airfield with an Unicom or CA/GRS service an information request might take this form: TANGAMBALANGA RADIO THRUSTER ZERO TWO EIGHT SIX REQUEST WIND AND TRAFFIC INFORMATION TANGAMBALANGA The response from the ground operator might be: THRUSTER ZERO TWO EIGHT SIX — TANGAMBALANGA RADIO — WIND IS ZERO FIVE ZERO ABOUT FIVE KNOTS — NO KNOWN TRAFFIC And the acknowledgment: ROGER THRUSTER ZERO TWO EIGHT SIX Thruster 0286 would then make a taxiing broadcast when appropriate. 5.4.6 CTAF response calls The difficulty for an inexperienced pilot is what to do — and say — in response to a broadcast from another aircraft that is perceived as a possible traffic conflict; particularly in an environment when high-speed turbo-prop RPT aircraft are operating. Maintaining situation awareness is a must for all pilots. All pilots must be aware of the positions and intentions of all other traffic in the vicinity, and — to determine possible traffic conflicts — able to project the likely movements of such traffic. This is not easy for anyone, particularly so if insufficient information is being provided. This is aggravated when aircraft are conducting straight-in approaches, so extra vigilance must be maintained, remembering the straight-in approach may be on the longest runway rather than the into-wind runway — or it might even be an 'opposite direction' landing. You must maintain a mental plan of the runways and associated circuit patterns, and overlay that with the current positions and announced intentions of other traffic. You must include the possibility of abnormal events; e.g. where is the missed-approach path for the turboprop aircraft currently on a straight-in approach on the longest runway? And you must keep other traffic informed of your intentions. Caution. When something unexpected happens in the circuit, for example a broadcast from another aircraft indicates you may be on a collision course, then naturally you will swivel around to locate the other aircraft. In these conditions there is a tendency to be distracted from flying the aeroplane — a dangerous position when at low speed and low altitude, particularly so if turning base or final. See 'Don't stall and spin in from a turn'. Although a recreational aircraft may have the right of way in a particular traffic situation, it is environmentally positive, courteous and good airmanship for recreational pilots to allow priority to RPT, agricultural aircraft, firefighting and other emergency aircraft, or for that matter any less-manoeuvrable heavy aircraft. The following is an example transmission from an aircraft on downwind which, after making a downwind broadcast, has monitored a straight-in approach call from an RPT turboprop and is now advising all traffic of the intent to extend its downwind leg and then follow the turboprop in — at a safe interval to avoid wake turbulence. TANGAMBALANGA TRAFFIC THRUSTER ZERO TWO EIGHT SIX EXTENDING DOWNWIND / RUNWAY ZERO SEVEN NUMBER TWO TO SAAB ON STRAIGHT-IN APPROACH TANGAMBALANGA An article — Talk Zone— in the May–June 2001 issue of CASA's Flight Safety Australia discusses CTAF radio procedure problems. Substitute 'CTAF' for the 'MBZ' references in the article. 5.4.7 En route procedures Class G airspace There are no mandatory reports for VFR aircraft operating en route in Class G airspace. Thus after departing the airfield vicinity, such aircraft are only required to maintain a listening watch on the 'appropriate frequency' and announce if in potential conflict with other aircraft — see AIP ENR 1.1 section 44. "ALL STATIONS (location)" instead of "(location) TRAFFIC" may be used for the called stations ID (refer AIP ENR 1.1 para. 68.4); for example: ALL STATIONS MAITLAND AREA THRUSTER ZERO TWO EIGHT SIX REQUEST ADVICE ON THE WEATHER CONDITIONS IN THE VFR LANE TO GLOUCESTER So what's the 'appropriate' frequency? This could be: the local Flight Information Area frequency — if so, calls to the Flight Information Service would be directed to Flightwatch which service is provided by either MELBOURNE CENTRE or BRISBANE CENTRE. If close to a major airport then perhaps (for example) SYDNEY RADAR. Frequency information blocks depicting Class E and G area frequencies, and the frequency boundaries, are included on the ERC-L, VNC and VTC charts. a listening watch could be maintained on the International Distress Frequency 121.5. See 'Can it ever be appropriate to monitor 121.5 MHz en route?'; a listening watch could be maintained on other specific frequencies; if below 3000 feet agl then perhaps listen out on Multicom 126.7 MHz ; when passing in or near the vicinity of a non-controlled aerodrome the designated frequency (otherwise 126.7 MHz or the FIA frequency ) for that airfield should be monitored to gain information on area traffic. Class E airspace As in Class G there are no mandatory reports for VFR aircraft operating en route in Class E airspace. Such aircraft are only required to maintain a listening watch on the 'appropriate frequency' and advise any potential conflict to the aircraft involved or to ATC. The choice of frequency would be much the same as in Class G with the addition of the appropriate ATC frequency. The latter must be used to take advantage of the Radar Information Service usually available in Class E. 5.4.8 Acquiring weather and other information in-flight Airservices Australia's Air Traffic Service [ATS] and the Australian Bureau of Meteorology provide several means of obtaining a limited amount of weather and other information while airborne: AERIS — the Automatic En Route Information Service network ATIS — the Automatic Terminal Information Service at some aerodromes AWIS — the Aerodrome Weather Information Service at some aerodromes. FLIGHTWATCH — the on-request Flight Information Service [FIS] provided by ATS. Further FIS information is contained in AIP GEN 3.3 section 2 and in the Flight Information Services section of ERSA GEN-FIS. AERIS AERIS is a network of 14 VHF transmitters that continually transmit routine weather reports for major Australian airports and a few other significantly sited aerodromes. Such information could be a guide to actual weather at airfields in the vicinity of those major airports. CASA has issued the following pilot guide showing the location of AERIS transmitters, the expected VHF coverage for aircraft at 5000 feet, the VHF frequencies and the aerodromes for which weather reports are available from each transmitter. See AIP GEN 3.3 section 2.8 and AIP GEN 3.5 section 7.4. More information will be found in ERSA GEN-FIS-1. ATIS ATIS is provided on either a discrete COMMS frequency or the audio identification channel (NAV band between 112.0 and 117.975 MHz) of an aerodrome navigational aid — generally in a control zone, but again such information could be a guide to actual weather at other airfields in the vicinity. The availability and frequency of the ATIS is specified in the ERSA airfield data. The continuous information broadcast includes the runway in use, wind direction (degrees magnetic) and speed, visibility, present weather, cloud and QNH. See AIP GEN 3.3 section 2.7. AWIS Australian Bureau of Meteorology automatic weather stations [AWS] are located at about 190 airfields. All the stations are accessible by telephone and about 70 are also accessible by VHF NAV/COMMS radio. The access telephone numbers and the VHF frequencies of the AWS can be found by entering the 'Location information' page and downloading the pdf for the relevant state. The information is also available in the aerodrome facilities section of ERSA and in the ERSA MET section. The AWIS uses pre-recorded spoken words to broadcast the current observations collected by the AWS — surface wind, pressure, air temperature, dew point temperature and rainfall. (For example, call 08 8091 5549 to hear the AWS aerodrome weather at Wilcannia, NSW.) In both the ATIS and AWIS reports, wind direction is given in degrees magnetic. This is because they are associated with aerodrome operations where runway alignments are in degrees magnetic, and conformity makes the crosswind estimate easier. Wind direction in all the text-based meteorological reports and forecasts is given in degrees true. At aerodromes where ceilometer and vismeter sensors are available, the AWIS will report cloud amount, height and visibility but the reliability of such observations is limited — the AWIS broadcasts the aerodrome weather derived from the AWS instrumentation and without any human input. The wind direction is expressed in degrees magnetic to the nearest 10°. Note that some of the VHF frequencies are in the NAV band; i.e. the broadcasts are on the airfield VOR frequency. More information is available in the MET section of ERSA online. Flightwatch Flightwatch is the call-sign of the on-request service — contained within Airservices Australia's FIS — which provides information of an operational nature to aircraft operating in Class G airspace. Whether Flightwatch is able to respond to an information request from an RA-Aus aircraft depends on workload and whether the requested information is readily available to the Flightwatch operator contacted — for example, the actual weather at the smaller airfields. The Flight Information Areas and FIS frequencies are depicted in ERC-L. An information request to Flightwatch should take the following form — note the Flightwatch operator may be managing quite a number of frequencies so the FIA frequency used (for example 119.4 MHz) must be included in the transmission: BRISBANE CENTRE FLIGHTWATCH THRUSTER ZERO TWO EIGHT SIX ONE ONE NINE DECIMAL FOUR REQUEST ACTUAL WEATHER LISMORE Acquiring QNH It is not mandatory for VFR aircraft to use the area QNH whilst en route. You may substitute the current local QNH of any aerodrome within 100 nm of the aircraft. Or, if the local QNH at the departure airfield is not known, you can — while still on the ground — just adjust the sub-scale so that altimeter reads the airfield elevation. Local QNH of airfields within 100 nm of the route might be acquired from AERIS, ATIS or AWIS; otherwise, area QNH can be obtained from Flightwatch: BRISBANE CENTRE FLIGHTWATCH THRUSTER ZERO TWO EIGHT SIX ONE ONE NINE DECIMAL FOUR REQUEST QNH AREA TWO TWO 5.4.9 The Surveillance Information Service [SIS] Transponder-equipped VFR aircraft operating in Class E or Class G airspace within the ATC radar coverage (the tan and green colours in the map approximate the lower level coverage) may request a no-cost radar/ADS-B information service [SIS] on the appropriate ATC frequency. (SIS was formerly known as the Radar Information Service [RIS].) The SIS is available to improve situation awareness by providing traffic information and position information or navigation assistance. VFR pilots may also request an ongoing 'flight following' service from SIS, so that ATC monitor your flight progress and can also help you avoid controlled airspace. The requested service will be provided subject to the controller's current workload — their primary responsibility is towards IFR aircraft — but there is usually no problem, particularly if you have filed a flight plan. Refer to AIP GEN 3.3 section 2.16 for the general procedure and remember that you still must comply with CAR 163A which states: 'Responsibility of flight crew to see and avoid aircraft When weather conditions permit, the flight crew of an aircraft must, regardless of whether an operation is conducted under the Instrument Flight Rules or the Visual Flight Rules, maintain vigilance so as to see, and avoid, other aircraft.' Position information and flight following request call format (Location) CENTRE CALL-SIGN (Altitude) (general vicinity) (destination) REQUEST POSITION INFORMATION AND FLIGHT FOLLOWING It is probably advisable to make a short contact call first then when the 'go ahead' response is received send the message. MELBOURNE CENTRE THRUSTER ZERO TWO EIGHT SIX THREE THOUSAND / VICINITY ROMSEY FOR POINT COOK REQUEST POSITION INFORMATION AND FLIGHT FOLLOWING RIS will ask you to 'squawk ident' and when your aircraft is identified will assign an unique transponder code plus the navigation information. When navigation assistance and flight following is no longer required advise SIS. 5.4.10 Sourcing frequency information The FIS frequencies to be used in Flight Information Areas and the frequencies at airfields (plus NDB and VOR frequencies) are either contained in ERSA or shown on PCA, ERC-L, VNC and VTC charts. The following table summarises the communications information available from those sources. PCA ERC-L VTC VNC ERSA VHF coverage at 5000 feet VHF coverage at 10000 feet HF network sector frequencies SIS frequencies Flightwatch frequencies FIA boundaries FIS frequencies at airfields Airfields where FIS contact possible from ground Airfield Unicom frequencies VOR/NDB frequencies and ID CTAFs STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

5.3.1 VHF radio wave propagation Electromagnetic waves travel in straight lines, but the transmission process is modified by interaction with the Earth's surface and by reflection, refraction and diffraction occurring within the atmosphere. The major source of modification of the paths of radio waves is the radiation-related layers within the ionosphere. The process by which the signal (the fixed carrier frequency plus the information) is conveyed between the transmitter and the receiver is propagation. Radio signal energy loss (attenuation) increases with distance travelled through the atmosphere or other materials. Propagation of radio waves within the high frequency [HF] band (the 'short wave' bands between 3 MHz and 30 MHz, with 12 aeronautical sub-bands in the domestic and international HF networks between 2850 and 22 000 kHz) is significantly modified by reflection/refraction within the ionospheric layers — a 'skipping' process that facilitates transmission over very long distances while using low power and small antennas. Propagation in the VHF band (30 MHz to 300 MHz), when using low power and small antennas, is chiefly in the form of a direct path. It is relatively unaffected by reflection, refraction and diffraction within the atmosphere; but is heavily attenuated by the Earth's surface and readily blocked, diffracted or reflected by terrain or structures — as experienced with VHF-band TV reception. Therefore for good reception of a VHF transmission there must be a direct line-of-sight [LOS] path between the transmitter antenna and the receiver antenna. The transmitter radio frequency [RF] output energy must be sufficient that the signal is not overly attenuated over that LOS distance. LOS distance LOS distance between a ground station and an aircraft station, or between two aircraft stations, is limited by the curvature of the Earth's surface, and dependent on the elevation/height of the two stations and the elevation of intervening terrain. The rule-of-thumb is: the maximum direct path distance (the distance to the horizon) between an aircraft and a ground station, in nautical miles, is equal to the square root of the aircraft height, in feet, above the underlying (flat) terrain. Actually it is 1.06 times the square root of the height, but for our purposes that can be ignored. Theoretical LOS distance to horizon Aircraft height (feet) Maximum LOS distance (nm) 10 3.2 100 10 1000 32 5000 70 10 000 100 Estimating the square root: mental calculation is easier if you ignore the two least significant digits of the height, then estimate the square root of the remaining one or two digits and multiply by 10. For example; height 3200 feet, the square root of 32 is between 5 and 6 — say 5.5 — and multiply by 10 = 55 nm LOS distance. Another example; height 700 feet, ignore 00, the square root of 7 is between 2 and three — say 2.6 — multiply by 10 = 26 nm LOS distance. For air-to-air communications the LOS distance is the sum of two 'distance to horizon' calculations; i.e. with one aircraft at 5000 feet the other at 10 000 feet, the maximum LOS distance will be 70 + 100 = 170 nm. It may be a bit more than that because of wave diffraction at the intervening horizon. Intervening mountain terrain may reduce the distance. Be aware that the LOS distance is the theoretical maximum range for direct-path VHF transmission/reception. The actual distance is likely to be a lot less depending on the transmitter/receiver system, the type and placement of the antenna, the quality of the receiver/headset system, and quite a few other considerations. The effective range may be as low as 5 nm or as much as the full LOS distance — but an effective range of 50 nm is probable for a good low-power installation. 5.3.2 Transceiver operation The apparatus that comprises an aircraft station is: an antenna system and feedline coaxial cable a radio transmitter/receiver unit or transceiver with modulating, transmitting, receiving, demodulating and power amplification circuits, plus mounting for the operator controls and displays a speaker/earphones and circuits to convert electromagnetic waves to sound waves a microphone and circuits to convert sound waves to electromagnetic waves the necessary interconnection cables, connectors and matching devices. All the system components must be correctly matched (electrically) to each other and to any separate cockpit intercommunication unit installed in a two-seat aircraft. Transmission Amplitude modulation [AM] of the fixed RF carrier wave, rather than frequency modulation [FM], is used in the aviation band to impress the voice information on the carrier wave generated by the transceiver. AM occupies less bandwidth than FM, consequently the AM channel spacing in the aviation COMMS band is only 25 kHz. When the transceiver is powered up and the pilot speaks into the microphone while depressing a 'press-to-talk' [PTT] button, the transmitter circuits amplify and broadcast, via the antenna system, the selected output frequency — 126.7 MHz for example — modulated with the audio frequencies from the microphone. This may also include the cockpit background noise. The low-fidelity R/T audio frequencies added are in the range 50 Hz to 5000 Hz; much the same as the domestic AM radio broadcast or the public telephone system. The transmission power of handheld transceivers is usually around 1 to 1.5 watts carrier wave. Fixed-installation transceivers are around 4 to 8 watts carrier wave. Some hand-held transceiver suppliers quote the peak envelope power [PEP] output which, for ordinary speech, is probably around three times the carrier wave value. The peak envelope power of an AM signal occurs at the highest crest of the modulated wave. Reception An aircraft antenna continually collects all passing RF energy in the band for which it is designed, which at any time will normally consist of many transmissions. The receiver tunes out all transmissions on all frequencies except one — the selected, or active, frequency. Signals on this frequency are demodulated to isolate the voice information from the carrier, amplify it and pass to the speaker system to convert to the sound waves heard in the earphones or speaker. Setting and changing frequencies The frequencies required are usually entered into a VHF transceiver via an electronic keyboard, concentric rotatable knobs, toggle buttons or a set of thumbwheels. There may be a switch to set channel steps at either 25 kHz or 50 kHz. Most transceivers allow the user to set one frequency into the unit as the active frequency and to set a second frequency as the standby frequency. All transmission and reception is done on the active frequency. Pressing a flip-flop, or similar switch, causes the standby frequency to become the active, and the active to become the standby. Thus, normal procedure prior to take-off is to set the airfield frequency as the active and the flight information area [FIA] frequency as the standby. When departing the airfield area, pressing the flip-flop will make the FIA frequency active for the required listening watch. On return to the airfield area pressing the flip-flop again restores the airfield frequency to active. Generally when selecting, keying or dialling another frequency during flight the new frequency changes the stand-by frequency. Some transceivers have 'dual-monitoring' capability – the ability to listen-in on more than one frequency (e.g. the FIA frequency and an airfield frequency) – but transmit on one frequency only. Features common to most transceivers a number of memory positions (5–50) allows storage of frequently used airfield/FIA and other frequencies an associated fast-scanning function of those stored frequencies instant access to the emergency/distress frequency of 121.5 MHz high and low transmit power settings for hand-held transceivers, giving a choice of minimum battery drain or maximum range hand-held transceivers are usually supplied with adapter(s) to connect the unit to the aircraft's COMMS (and NAV) antenna(s) hand-helds usually have key locking facilities to prevent inadvertent frequency changes or transmissions hand-helds may also provide access to the 200 channels in the NAV band between 108.00 and 117.975 MHz, which gives a limited VOR capability if the transceiver can be adapted to a NAV dipole antenna. The main advantage provided by this facility is access to any ATIS or AWIS frequencies between 112.1 and 117.975 MHz. Headsets The cockpits of powered recreational and sport aircraft are notoriously noisy and those close to a high rpm two-stroke engine are the worst. Propeller tip speeds may approach mach 0.8 and generate noise at fairly high frequencies while the engine produces noise in the low to middle frequencies. External airflow noise may or may not be significant depending on the existence and effectiveness of cockpit sealing. In all, the cockpit noise level may approach 100 dB and long-term exposure to noise above 90 dB will damage hearing. Also, noise and vibration add to pilot fatigue and the low-frequency engine noises below 300 Hz are particularly fatiguing. Consequently all pilots must wear some form of hearing protection — which may be incorporated within a good quality protective helmet. Headsets serve a dual purpose in providing hearing protection whilst improving communications. The basic headset consists of two earphones with some physical sound sealing capability plus a directional microphone mounted on an adjustable boom, so that it can be positioned within 1–3 cm in front of — and square on to — the pilot's lips when transmitting. The headset cables are jacked into the transceiver input/output sockets or patched via a cockpit intercom unit. Standard headsets may not be able to be used with hand-held transceivers without an adapter device. Additional facilities — such as individual volume control on each earphone with an electronic noise reduction system and cockpit noise cancelling microphones — are available. You can get headsets specifically designed for two-stroke engine noise reduction. Normal headsets rely solely on passive noise reduction — creating a physical barrier around the ear to attenuate noise — which usually works quite well for middle to high-frequency sound but doesn't block low-frequency engine noise and background rumble. Active noise reduction technology uses electronics to determine the amount of low-frequency (50–600 Hz) engine and other noise entering the system and then generating out-of-phase noise, in the same frequency range; this counters the background noise and leaves a soft 'white' noise in the headphones. But the technology doesn't significantly affect the higher-frequency noise. Using the squelch control All transceivers have some form of ON/OFF/TEST/VOLUME control. As aircraft cockpits are very noisy, the output volume control must be set fairly high. This of course amplifies the weak atmospheric background radio frequency noise — the hash — which is always there when no strong transmissions are being heard on the active frequency; this hash can be quite annoying. The 'squelch' or 'gain' or 'RF gain' or 'sensitivity' control is an adjustable filtering device which, for operator comfort, can be set just to filter out the hash but still allow any strong signals to be switched through. The squelch control should only be switched on and adjusted when contact with the active frequency has been established, volume set and headset connection checked. Otherwise, when the signal is weak, there is a high risk of also filtering out the active frequency transmissions which, in effect, turns the receiver off. Some transceivers have an automatic gain control. In which case, pressing the test facility will override the squelch, allowing the background hash to be heard. 5.3.3 Wave length and antennas It is stated in the electromagnetic spectrum section that the frequency in MHz = 300/wavelength in metres — or restated, the wavelength in metres = 300/MHz. Thus the wavelengths involved in the aviation VHF COMMS band, 118.00 to 136.975 MHz, are from 2.54 metres to 2.19 metres and the mid-point is about 2.37 metres. The Multicom frequency — 126.7 MHz — has a wavelength of 300/126.7 = 2.37 metres. Wavelength is important as the efficiency of the antenna (a passive electrical conductor that radiates the signal energy when transmitting, or collects signal energy when receiving) partly depends on its length relative to the frequency wavelength. Most ineffective radio installations are because of ineffective antenna installations and/or RF interference generated by the engine ignition system or the aircraft's electrical components. Dipole antennas Aircraft COMMS antennas are usually dipoles or monopoles. A dipole is an antenna that is divided into two halves insulated from each other. Each half is connected to a feedline (coaxial cable and RF BNC series bayonet connectors) at the inner end, which routes the RF energy between the antenna and the transceiver. The length of each half is about 5% less than the mid-point quarter-wave — usually about 56 cm, or 22 inches. (The mid-point quarter-wave is 2.37/4 =59 cm.) Rather than being set out end-to-end horizontally, each half is canted up about 22.5° to form an internal angle of around 135°, which prevents a deep "null" zone off both ends. NAV or COMMS dipoles may be mounted within the fuselage if the aircraft is not metal-skinned or metal-framed. A NAV antenna must be horizontally polarised; i.e. mounted horizontally. The two halves of a COMMS dipole antenna can be end-to-end vertically mounted with a centre feedline and built into the fin of a fibre-reinforced composite aircraft — but not if it is carbon fibre. Similarly a half-wave dipole antenna might be used on a trike where the longer length can be mounted vertically end-to-end and strapped to the king-post. The telescopic 'rabbit's ears' antennas used with the old black and white TVs were dipoles — as channels (frequencies) were changed the length was adjusted to maintain the half-wavelength dimension. Monopole or whip antennas The most common recreational aircraft COMMS antenna — the monopole — is just one half of a dipole; i.e. quarter-wavelength. (To calculate antenna quarter-wavelength in centimetres, divide 7130 by the frequency; i.e. 7130/126.7 = 56 cm.) Thus the monopole is usually about 56 cm long, mounted vertically (vertically polarised) — normally on the top of the fuselage (away from the undercarriage legs) — with the feedline conductor to/from the transceiver connected to the bottom end of the antenna. The 56 cm length should provide very good mid-frequency reception and reasonable reception at the lower and upper ends of the COMMS band and, usually, increasing the thickness of the antenna element increases its effectiveness. The antenna element may be enclosed within a streamlined fibreglass fairing to add structural strength. To replace the other half of the dipole a conductor system is placed just below the antenna to serve as an earth ground — a ground plane, ground screen or at least four ground radial strips or rods, connected to the coax cable shielding. The radius of the ground equals the length of the antenna; i.e. 56 cm. In a metal-skinned aircraft the fuselage acts as a ground plane, which is electrically insulated from the antenna by a very small gap. The photo shows the ground plane, in Leo Powning's Jodel project, mounted under the ply turtle deck (looking aft). The centre plate and four 25 mm wide radials are cut from light gauge aluminium sheet sold in hardware stores. Total dimension from the antenna socket to the end of each radial is 57 cm — about the mid-point of the COMMS band. The sloped radials provide an antenna impedance of approximately 50 ohms. The 50 ohms coax connecting the antenna is attached to the turtle deck formers with plastic P clips. Transmission/reception pattern Because of antenna characteristics and airframe shielding, the radiation/reception pattern of the antenna will be weaker in some directions and may even exhibit null zones. The easiest way to check this is to tune in the continuous broadcast — at a reasonable (say 30 nm) distance — from a known ATIS, AWIS or AERIS location, then circle while listening to the signal strength. A few turns should be sufficient to plot the directions, relative to the aircraft's longitudinal axis, from which signal strength weakens and/or reduces to nil. Because the attitude of the aircraft also affects transmission/reception, it is advisable to first fly non-banked turns to ascertain the normal pattern then fly banked turns to check the consequent effects. Impedance matching All VHF transceivers are designed for a standard load (impedance) of 50 ohms. Ideally the coaxial cable, BNC connectors and antenna match that 50 ohm impedance all the way; then all the transmission power sent to the antenna will be radiated as RF energy. However, the resonant frequency of any antenna will match only one frequency, and the COMMS operational frequencies range over 19 MHz. So for most transmission frequencies the antenna will exhibit positive or negative reactance (or impedance), which results in the phenomenon known as 'stationary' or 'standing' waves in the feed line and reduces the output of the antenna. Also the incoming signals will be weaker. The RF performance of the antenna system is expressed in terms of the voltage standing wave ratio [SWR or VSWR]. A perfect (but most unlikely) antenna system would have a SWR of 1:1 but generally a SWR less than 2:1 results in quite acceptable performance and limits transceiver overheating. The Microair 760 — described in the next module — requires a SWR between 1.3:1 and 1.5:1. If the transmission performance is okay then the reception performance should also be okay. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

5.2.1 Radiotelephony pronunciation (AIP GEN 3.4 section 4) A phonetic alphabet is used in radiotelephony [R/T] communications when transmission of individual letters is required. This phonetic alphabet was originally developed by the North Atlantic Treaty Organisation as an international alphabet for use by the armed forces of the NATO nations. Letters Phonetic Pronunciation Phonetic Pronunciation A ALFA AL fah B BRAVO BRAH voh C CHARLIE CHAR lee D DELTA DELL tah E ECHO ECK ho F FOXTROT FOKS trot G GOLF GOLF H HOTEL hoh TELL I INDIA IN dee A J JULIETT JEW lee ETT K KILO KEY loh L LIMA LEE mah M MIKE MIKE N NOVEMBER no VEM ber O OSCAR OSS cah P PAPA pah PAH Q QUEBEC keh BECK R ROMEO ROW me oh S SIERRA see AIR rah T TANGO TANG go U UNIFORM YOU nee form V VICTOR VIK tah W WHISKY WISS key X X-RAY ECKS ray Y YANKEE YANG key Z ZULU ZOO loo Numbers The R/T pronunciation of numbers should be the following phonetic form: 0 ZE–RO 5 FIFE 1 WUN 6 SIX 2 TOO 7 SEV en 3 TREE 8 AIT 4 FOW er 9 NIN er Hundred HUN dred Thousand TOU SAND Decimal DAY SEE MAL Expressing numbers All numbers used in the transmission of altitude, cloud height and visibility information — that contain whole hundreds and whole thousands — must be transmitted by pronouncing each digit in the number of hundreds or thousands followed by the word HUNDRED or THOUSAND as appropriate, but without the suffix 'feet'; e.g.: ALTITUDE: (800 feet) – "EIGHT HUNDRED" (1500 feet) – "ONE THOUSAND FIVE HUNDRED" (4750 feet) – "FOUR SEVEN FIVE ZERO" (10 000 feet) – "ONE ZERO THOUSAND" CLOUD HEIGHT: (2200 feet )– "TWO THOUSAND TWO HUNDRED" (4300 feet) – "FOUR THOUSAND THREE HUNDRED" VISIBILITY: (1500 feet) – "ONE THOUSAND FIVE HUNDRED" (3000 feet) – "THREE THOUSAND" All other numbers, except VHF frequencies, must be transmitted by pronouncing each digit separately; e.g.: HEADING (the words 'degrees' and 'magnetic' are not transmitted): (150° M) – "ONE FIVE ZERO" (080° M) – "ZERO EIGHT ZERO" (305° M) – "THREE ZERO FIVE" WIND DIRECTION (the word 'degrees' is transmitted): (020°) – "ZERO TWO ZERO DEGREES" (100°) – "ONE ZERO ZERO DEGREES" (210°) – "TWO ONE ZERO DEGREES" WIND SPEED: (10 knots) – "ONE ZERO KNOTS" (15 knots, gusting to 25) – "ONE FIVE KNOTS GUSTING TWO FIVE" ALTIMETER SETTING – QNH: (995 hPa) – "NINE NINE FIVE" (1010 hPa) – "ONE ZERO ONE ZERO" (1027 hPa) – "ONE ZERO TWO SEVEN" VHF frequencies are a bit unusual because 25 kHz spacing is gradually being introduced in Australia as frequency congestion becomes apparent. However, currently only 50 kHz spacing operates in Class G airspace. If the frequency is a 50 kHz multiple then all significant digits are transmitted including the first zero after the decimal point: (122.0) – "ONE TWO TWO DECIMAL ZERO" (122.15) – "ONE TWO TWO DECIMAL ONE FIVE" (126.05) – "ONE TWO SIX DECIMAL ZERO FIVE" (126.7) – "ONE TWO SIX DECIMAL SEVEN" If the frequency is a 25 kHz multiple (i.e. the second and third digits after the decimal point are 25 or 75) then the sixth digit is inferred as 'FIVE' and not transmitted: (122.025) – "ONE TWO TWO DECIMAL ZERO TWO" (122.525) – "ONE TWO TWO DECIMAL FIVE TWO' (122.075) – "ONE TWO TWO DECIMAL ZERO SEVEN" (122.675) – "ONE TWO TWO DECIMAL SIX SEVEN" 5.2.2 Expressing time (AIP GEN 3.4) The 24-hour clock system is used in R/T transmissions. The hour is indicated by the first two figures and the minutes by the last two figures, e.g.: (0001 hrs) – "ZERO ZERO ZERO ONE" (1920 hrs) – "ONE NINE TWO ZERO". Time may be stated in minutes only (two figures) in R/T communications when no misunderstanding is likely to occur. Current time in use at a station is stated to the nearest minute in order that pilots may use this information for time checks. Australian civil aviation uses Coordinated Universal Time [UTC] for all operations. The suffix 'Zulu' is appended when procedures require a reference to UTC, e.g.: (0920 UTC or 0920Z) – "ZERO NINE TWO ZERO ZULU" (0115 UTC or 0115Z) – "ZERO ONE ONE FIVE ZULU". To convert from Australian Standard Time to UTC: Eastern Standard Time subtract 10 hours Central Standard Time subtract 9.5 hours Western Standard time subtract 8 hours. 5.2.3 Standard words and phrases (AIP GEN 3.4) The following words and phrases are to be used in radiotelephony communications, as appropriate, and have the meaning given: ACKNOWLEDGE Let me know that you have received and understood this message. AFFIRM Yes. APPROVED Permission for proposed action granted. BREAK I hereby indicate the separation between portions of the message (to be used where there is no clear distinction between the text and other portions of the message). CANCEL Annul the previously transmitted clearance. CHECK Examine a system or procedure (no answer is normally expected). CLEARED Authorised to proceed under the conditions specified. CONFIRM Have I correctly received the following ... ? or Did you correctly receive this message ... ? CONTACT Establish radio contact with ... CORRECT That is correct. CORRECTION An error has been made in this transmission (or message indicated) the correct version is ... DISREGARD Consider that transmission as not sent. HOW DO YOU READ What is the readability (i.e. clarity and strength) of my transmission? See 'clarity of transmission'. I SAY AGAIN I repeat for clarity or emphasis. MAINTAIN Continue in accordance with the condition(s) specified or in its literal sense, e.g. "Maintain VFR". MAYDAY My aircraft and its occupants are threatened by grave and imminent danger and/or I require immediate assistance. MONITOR Listen out on (frequency). NEGATIVE "No" or "Permission is not granted" or "That is not correct". OVER My transmission is ended and I expect a response from you ( not normally used in VHF communication). OUT My transmission is ended and I expect no response from you ( not normally used in VHF communication). PAN PAN I have an urgent message to transmit concerning the safety of my aircraft or other vehicle or of some person on board or within sight but I do not require immediate assistance. READ BACK Repeat all, or the specified part, of this message back to me exactly as received. REPORT Pass me the following information. REQUEST I should like to know or I wish to obtain. ROGER I have received all of your last transmission (Under NO circumstances to be used in reply to a question requiring READ BACK or a direct answer in the affirmative or negative. Do not use the term 'COPY THAT' or double click the transmit button.) SAY AGAIN Repeat all or the following part of your last transmission SPEAK SLOWER Reduce your rate of speech. STANDBY Wait and I will call you. VERIFY Check and confirm with originator. WILCO I understand your message and will comply with it. (Do not use the term 'COPY THAT' or double click the transmit button.) Clarity of transmission The response to the query 'HOW DO YOU READ?' or 'REQUEST RADIO CHECK' is phrased in accordance with the following readability scale: Unreadable Readable now and then Readable but with difficulty Readable Perfectly readable. Phraseologies The phraseologies to be used in communications between ATS and pilots in various circumstances are detailed in AIP GEN 3.4 section 5. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

5.1.1 The aircraft station and aeronautical mobile station class licence All operational radio transmitters are required to be licensed by the Australian Communications and Media Authority [ACMA]. To avoid the need to license individual VHF and HF aviation radiotelephony transceivers (and other transmitters carried in aircraft such as transponders or radio distress beacons) the ACMA issues a class licence. The current Radiocommunications (Aircraft and Aeronautical Mobile Stations) Class Licence 2006 [CL2006] replaced the Radiocommunications (Aircraft Station) Class Licence 2001. CL2006 authorises the operation — by qualified operators — of a range of aeronautical radiocommunications and radionavigation equipment fixed to, or carried on board, all aircraft including recreational aircraft. It also authorises most ground-based aeronautical mobile radiocommunications equipment operating on the common group of aviation frequencies. An aircraft station may only be operated (i.e. transmitting) when it is on board an aircraft, thus you cannot operate your hand-held transceiver as an aircraft station unless you are in an aircraft and identify yourself with that aircraft's station call sign. If any condition of CL2006 is breached (for example, transmitting on a frequency not encompassed by the class licence) the operator is no longer authorised to operate under the class licence. In this instance, the operator would be liable for prosecution by the ACMA. An aeronautical mobile station (and an aircraft station) may only be used for communications that relate to: the safe and expeditious conduct of a flight an emergency a matter that relates to the particular occupation or industry in which the aircraft to which the aircraft station relates is engaged; or the aeronautical mobile station is engaged. Typically a flight instructor on the ground with a hand-held transceiver supervising a student in the circuit is operating as an aeronautical mobile station. The same might apply to a person advising traffic conditions at a fly-in. The operator of an aeronautical mobile station must use a form of identification that clearly identifies the mobile station. Equipment standards Various equipment compliance requirements, specifications and mandatory technical standards apply to radiotelephony equipment intended to equip an aircraft station under the class licence. If it is a fixed installation only Civil Aviation Safety Authority [CASA] approved apparatus may be used; refer to AIP GEN 1.5 para 1.1. An ACMA approved and licensed hand-held (or demountable) VHF aviation band radiotelephone may be used by pilots of recreational aircraft operating in Class G airspace, provided that the equipment is able to be operated without adversely affecting the safety of the aircraft. Refer to AIP GEN 1.5 para 1.5. Recreational aircraft operating in Class E airspace must be equipped with a serviceable VHF communications system. The AIP Book is perhaps at variance with the CARs and CAOs so it is not absolutely clear that ACMA approved hand-held units are acceptable in Class E or other controlled airspace. The standard for hand-held equipment performance is that set out in the Australia/New Zealand Standard 4583:1999 (and later). Aircraft station identification All transmitters are required to have an individual identification or call-sign that clearly identifies the station. The call-sign for recreational and sport aircraft registered with CASA is generally the last three characters of the registration marking. The mandatory call-sign for RA-Aus registered aircraft is the aircraft type followed by the four-digit RA-Aus registration number, for example "Thruster zero two eight six". The call-signs (where 'a' represents an alphabetic character and 'n' a numeric character) for recreational aircraft are: Recreational aircraft type Call-sign format RA-Aus (all groups) (aircraft type)nnnn Trikes (HGFA registered) TRnnn or TCnnn Hang Gliders HGnnnn Paragliders HGnnnn Gyroplanes Gnnn and Gnnnn Sailplanes (VH-) aaa Balloons (VH-) aaa General aviation (VH-) aaa Aeronautical stations The backbone high frequency [HF] and very high frequency [VHF] civil aviation radiotelephone communications network is owned and operated by Airservices Australia. In addition, regular public transport companies have their own communications networks. Similarly other 'fixed' ground stations could be licensed by ACMA for operation in the aviation VHF band by aero clubs, flying schools and parachute clubs; or by other organisations providing an aerodrome Unicom service. In the regulations such fixed ground stations are called aeronautical stations. However, aero clubs, flying schools and parachute clubs are more likely to operate as 'aeronautical mobile stations'. The military aviation network utilises ultra high frequency [UHF] at military airfields. Radio frequency symbols Radio frequencies are described in terms of hertz or 'cycles per second'. The symbols used in the aviation bands are kHz (thousand cycles per second e.g. 2850 kHz) in the HF band and MHz (million cycles per second, e.g. 126.7 MHz) in the VHF and UHF bands. 5.1.2 Communication limitations Communications between aircraft stations; and between aircraft stations, aeronautical stations and aeronautical mobile stations. A person may operate an aircraft station to communicate with another aircraft station, aeronautical station or aeronautical mobile station only if the communication relates to: the safe and expeditious conduct of flight an emergency a matter that relates to the particular occupation or industry in which the aircraft, to which the aircraft station relates, is engaged proper call-signs must be used. Communications between aeronautical mobile stations and aircraft stations. A person who is a member of an aero club, flying school or parachute club may operate an aeronautical mobile station to communicate with an aircraft station for the particular activity only if: the aeronautical mobile station is owned and operated by an aero club, flying school or parachute club; and the communication occurs when the aircraft to which the aircraft mobile station relates is engaged on a flight to or from the aerodrome at which the aeronautical mobile station is located. Unauthorised communications From the above, it is evident that an aircraft station may not transmit private or personal messages; i.e. information not pertaining to operational requirements. Nor can an unallocated frequency within the aviation VHF band be used for communications. In addition, all transmissions must be in the English language, use standard phraseology and a phonetic alphabet, and may not include: profane or obscene language deceptive or false information improper use of another call-sign. Secrecy of communications CL2006 holders are legally bound not to divulge, without authority, the content of any radiotelephony message sent or received. 5.1.3 Aircraft station operating frequencies Airservices Australia is nominated by the ACMA to approve all frequency assignments made in the aviation bands. Radiocommunications with Airservices Australia's air traffic services [ATS] are chiefly conducted in the aviation VHF communications [COM or COMMS] band, 117.975 to 136.975 MHz where, at 0.025 MHz (25 kHz) steps, there are 760 channels possible. Currently, channel separation in the Australian aviation band, except in Class A airspace, is generally at 0.1 MHz (100 kHz) or 0.05 MHz (50 kHz) spacing. However 25 kHz channel frequencies may be allocated for Class C, D and E airspace, along with rules for frequency stability standards to reduce inter-channel interference. (If a current receiver/transmitter displays frequencies with three decimal places it is likely to meet stability standards; for more information read 'Channel squeeze update' in the May – June 2009 issue of Flight Safety Australia.) There is a dedicated aviation VHF band from 108.1 to 117.975 MHz for operation of navigation facilities, such as VOR systems. This is the 'NAV band' while the full aviation VHF band from 108.00 to 136.975 MHz is the 'NAV/COM band'. Some specific aviation operational frequencies are: Aero club operations — 119.1 MHz Flying school operations — 119.1 MHz Fire spotting — 119.1 MHz Parachute club operations — 119.2 MHz Aviation sport — 120.85 MHz Emergency location — 121.5 MHz (plus 243.0 and 406.025 in the UHF band) Glider/sailplane operation — 122.5, 122.7, 122.9 MHz Fishing or agricultural operations or stock mustering — 122.8 MHz Pilot-to-pilot communications — 123.45 MHz Traffic information aircraft broadcasts — 126.35 MHz Aircraft industry testing — 129.1 MHz Crop dusting — 129.6 MHz Aerodrome operator, including refueller — 129.9 MHz Air show — 127.9 MHz Charter and other purposes not listed — 126.4, 128.9, 135.55 MHz Search and rescue only — 121.5, 123.1, 123.2 MHz (plus the 156.3, 156.8 MHz marine band frequencies) Inter-pilot air-to-air communication frequencies at airfields Within Class G airspace are some areas, surrounding all reasonably active airfields where, to maintain safe separation, pilots are required to exercise particular monitoring and reporting procedures between each other; and to self-administer movement priorities where appropriate. These are common traffic advisory frequency [CTAF] areas, and the VHF frequency to be used at particular CTAFs is specified in ERSA and VNC, VTC, PCA and ERC-L charts. Some CTAF airfields may have a private ground-based 'Unicom' information service, the operating frequency of which is the same as the airfield VHF frequency specified in ERSA. For further information on operations at, or in the vicinity of, airfields in Class G airspace see Radiotelephony communications and procedures in Class G airspace. Inter-pilot air-to-air communication frequencies en route Interpilot air-to-air communications can be conducted on frequency 123.45 MHz. When aircraft are operating in remote areas out of range of VHF ground stations, then 123.45 MHz is the regional air-to-air channel. Communications between aircraft on 123.45 MHz are restricted to the exchange of information relating to aircraft operations and only the proper call-signs may be used. 5.1.4 Radio operator qualification Operators of aircraft stations must be qualified in accordance with the requirements of the CL2006, which states: A person may operate an aircraft station or an aeronautical mobile station only if the person is qualified to operate the station in accordance with the Civil Aviation Regulations and the relevant Civil Aviation Orders. The Chief Flying Instructor of an approved flight training facility may recommend issue of the radio operator's endorsement after evaluation of the applicant's demonstrated performance during flight operations and in an oral or written examination. The examination will cover the syllabus listed in the RAAOs manuals. For example see the RA-Aus Operations Manual section 3.08. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)

It started as a dream to link outback towns by air and grew into a global icon, flying more than 50 million passengers a year around the world. Over the past century, the legacy of Qantas has grown to become much more than an airline — the flying kangaroo is now a globally recognised brand. Today, 16th November 2020, 100 years since the airline was founded in western Queensland, a good-natured outback rivalry over the story of the airline's formation shows no signs of losing breath, as three towns lay claim to being the birthplace of Qantas. Longreach, Cloncurry and Winton — located in the state's remote outback — each say they are the true home of the national carrier. "It's a very proud western Queensland story that couldn't have happened anywhere else," said Jeff Close, an amateur historian from the town of Winton, 1,300 kilometres north-west of Brisbane. Jeff Close is so passionate about Winton's role in the Qantas story, he wrote a play about the airline for its 90th anniversary in 2010.(ABC Southern Queensland: Nathan Morris) Dream springs from Cloncurry riverbed A century ago, on November 16, 1920, Queensland and Northern Territory Aerial Services Limited was registered. Its co-founders, Sir Hudson Fysh and Paul McGinness, had wanted to establish an airline to alleviate the tyranny of distance facing residents living in Australia's outback. Sir Hudson Fysh (left) and Paul McGinness (right) wanted to create an airline to connect outback towns.(Supplied: Qantas Founders Museum) "We go with what Sir Hudson Fysh himself said," Mr Close said. "[Qantas] was conceived in Cloncurry, born in Winton and grew up in Longreach." In 1919, then prime minister Billy Hughes announced a prize of 10,000 British pounds for a Great Air Race for Australians who wanted to fly home from Great Britain after World War I. Fysh and McGinness were tasked with surveying possible aircraft landing strips across western Queensland and the Northern Territory. As they travelled over rough terrain from Longreach to Darwin in a Ford Model T, at an average speed of 25 kilometres per day, the pair hatched a plan to establish an air service connecting remote communities. Paul McGinness (centre) and Sir Hudson Fysh (right) were in outback Queensland preparing for the Great Air Race in 1919 when they devised a plan to establish an airline.(Supplied: Qantas Founders Museum) But according to Hamish Griffin, a Cloncurry resident and advocate for cheaper regional airfares, it was in the dry riverbed of the Cloncurry River that the idea really gained traction. "If people really, really do a deep dive into the story of how it came about, they would really know that Cloncurry was definitely the founding place of Qantas," Mr Griffin said. In December 1919, McGinness came to the aid of a wealthy grazier whose car had broken down in the riverbed. They formed a friendship and the grazier, Fergus McMaster, agreed to financially back the plans for an airline. It was in the near-dry riverbed of the Cloncurry River that Qantas co-founder Paul McGinness met grazier Fergus McMaster, who went on to financially back the airline.(Supplied: Qantas Founders Museum) Early moneymen hail from Winton But Mr Close says it was 347 kilometres away in Winton, to the south-east of Cloncurry, that Qantas really took flight. "Winton really is and was the mover and shaker as … the early money mainly came from Winton," Mr Close said. He said five of the company's eight original shareholders were from Winton. The Winton Club, site of the airline's first board meeting in 1921.(ABC Western Queensland: Ellie Grounds) The Winton Club is filled with Qantas memorabilia.(ABC Western Queensland: Ellie Grounds) "They put the money up and got it going," Mr Close said. "They had the drive, the expertise, the youth, the exuberance, the need … Winton was just in the right place at the right time." The airline's first board meeting was held at the Winton Club on February 10, 1921. The club is still there today, proudly displaying the company's original articles of association, which list Winton as the airline's headquarters. Mr Close feels so strongly about Winton's role in the airline's story, he wrote a play about Qantas and performed it at the Winton Club on the airline's 90th anniversary. Next year he plans on putting on another play, to recreate the first board meeting in the room it took place in a century earlier. Longreach becomes airline's home A decision was made at that meeting to move operations to Longreach, for logistical reasons. The town is now home to the Qantas Founders Museum, where visitors can tour significant aircraft including the Super Constellation, the first pressurised plane, and the first jet aircraft the airline owned — the Boeing 707-138 VH-EBA, named "City of Canberra". A DH-50 fuselage under construction in the Longreach hangar circa 1926.(Supplied: Qantas Founders Museum) "Longreach had the rail head, the major services came into Longreach, the railway stopped here," said Tony Martin, the museum's CEO. "It made sense for Longreach to be the hub to start the airline." The hangar built in 1922 to house the planes is now a national heritage-listed site. It's the oldest civil aviation building in Australia. "It's the place where the airline began its operations," Mr Martin said. "[Qantas is] one of the only airlines in the world to build their own aircraft, and they did it here in Longreach. Qantas built seven DH-50 planes in the Longreach hangar from 1926 to 1929.(ABC Western Queensland: Ellie Grounds) Qantas is 'Vegemite, thongs … it's home' A century on, the residents of Cloncurry, Winton and Longreach still like to wind each other up about which town can really claim to be the birthplace of Qantas. Mr Griffin said that because the museum was located in Longreach, it could be "forgiven" for portraying itself as the birthplace of the airline. But he said, with a wry smile, the record needed to be set straight. "It's our time to shine. Cloncurry —we're the place." The Qantas Founders Museum in Longreach is home to some of the airline's most iconic planes.(ABC Western Queensland: Ellie Grounds) Mr Close said the three towns squabbled over the airline's history like siblings. "Like kids in a family we can all have our scraps, but in the end we are united very much by our pride in Qantas," he said. With a grin, Mr Martin admitted he could be guilty of stoking the "great friendly rivalry" between the towns. "If I could say to our neighbouring towns, I guess Longreach, like Qantas, had the vision to tell the story here," he said. Tony Martin admires the four-passenger De Havilland DH-50, the first purpose-designed airliner used by Qantas.(ABC Western Queensland: Ellie Grounds) But, all jokes aside, he said the airline's 100th anniversary was a chance to celebrate one of western Queensland's greatest exports. "For us to be part of a story that's 100 years old, and is such a global story...," he said. "Qantas, it's Vegemite, it's thongs, it's koala bears, it's up there with that branding. It's home."