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Rev. 42c — page content was last changed October 12, 2009
consequent to editing by RA-Aus member Dave Gardiner
|Flight Planning and Navigation|
The four elements of aerial navigation are position, direction, distance and time — and distance by time is ground speed. There are four systems or techniques of air navigation — pilotage, dead reckoning, position-fixing and homing. Pilotage and dead reckoning are the primary navigational techniques for pilots of light recreational aircraft and, like many air navigation terms, they are centuries-old nautical terms.
PilotagePilotage is navigation by visual reference to landmarks — the art of visual track-keeping — which requires that the ground is continually in sight. In the early days, all air navigation was by pilotage with some crude dead reckoning. Indeed the first Pilots' Directions published by Elrey B. Jeppesen in the 1920s, for the early air mail pilots in the USA, were just notes about the landmarks along a route. As accurate aerial charts became available then aerial dead reckoning became much more refined.
Map reading is the essence of pilotage. It entails: a continuous in-flight survey of the planned route (pre-plotted on the chart); identification of the upcoming chart features on the ground (i.e. reading from map to ground); and determining the actual location relative to the planned position. Following the determination of that position (and thus the actual path over the ground) dead reckoning is then used to determine the 'navigation solution':
Only when uncertain of your position will it be necessary to note prominent ground features and their relative positions, and then find those features on the map; i.e. reading from ground to map. Map interpretation is an acquired skill. An inability to relate the map to the ground features in view is a common experience on the initial attempts. Some find it very difficult to master. In the more remote, and rather featureless, areas of Australia what seem to be the major features on the surface may not be shown on the chart, and vice versa.
Dead reckoningDead reckoning [DR] is deriving the current position, or a future position, mathematically from a planned position or the last known position. DR for light aircraft is, or should be, essentially simple navigation by clock, compass and mental arithmetic. Most of the DR for RPT and military aircraft is done within the electronic circuitry of advanced navigation systems such as inertial navigation systems [INS], which calculate a new position, from the previous position, about 100 times per second.
DR has a limitation in that errors in plotting, wind velocity estimation, course steering and timing are cumulative, and the true position of the aircraft can't be verified unless it can be determined by pilotage (landmark reference) or some other position fixing technique.
Position-fixingAeronautical position-fixing techniques are usually radio-based. They encompass simple techniques such as plotting the intersection of the bearings from two radio beacons, through to more complex systems such as VOR/DME which is both position-fixing and homing. Such systems usually incorporate some degree of electronic DR. The Global Positioning System [GPS] is a continuous position-fixing or electronic pilotage system plus electronic dead reckoning to calculate the new bearing to the next waypoint. The non radio-based position-fixing techniques are celestial — star sights or sun sights.
HomingHoming is radio-based and encompasses non-directional radio beacon [NDB] and VHF omnirange [VOR] homing through to instrument landing systems [ILS].
The pages of this navigation guide summarise the essentials of pilotage and manual DR. A section on supplementary navigation techniques provides an introduction to NDB, VOR and GPS for VFR recreational pilots. In addition there is a module describing electronic planning and navigation systems for light aircraft.
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Before undertaking a cross-country flight, the pilot must know the total usable fuel capacity and the rate of consumption at the planned cruising speed. The fuel consumption rates supplied by engine/aircraft manufacturers, unless contained in a formal pilot's operating handbook, must be viewed somewhat sceptically; they may be achievable with an 'as new' engine cruising at the best endurance power setting, but are not reflective of the consumption at a more useful cruise speed, say that at 75% power. Fuel must be allowed for consumption at the departure airfield, for the climb and for circuit delays and landing at the destination or an alternate airfield. In addition, the pilot is required to plan a fixed fuel reserve. The reserve amount planned is a matter of personal discretion and the capacity of the fuel tank. It should not be less than 30 minutes in good flying conditions but a greater amount — perhaps 60 minutes — when there is any doubt about the wind velocities or other conditions.* This reserve should not be planned for use; i.e. whether the aircraft is finally landed at the planned destination or the alternate airfield there ought to be at least 30 minutes fuel in the tanks. The fixed fuel reserve concept still applies even if the planned flight is just a local flight terminating at the departure airfield — or a session of circuits and touch'n go's.
*The CASA civil aviation advisory publication CAAP 234-1 'Guidelines for aircraft fuel requirements' provides information and guidance on the fuel requirements for aircraft required by CAR 234. CAAP 234-1 suggests a 45 minute fixed fuel reserve for piston engine VFR aeroplanes. For recreational aircraft I suggest 45 minutes for engines of 80 hp and above and 30 minutes fixed reserve for engines below 80 hp, but read CAAP 234-1.
It is vital to be able to measure fuel consumption during flight, so a reasonably accurate fuel contents gauge, sight gauge or an in-flight view of the fuel tank content is necessary. It is good practice to maintain a history log in the aircraft where the actual fuel consumption per flight hour is entered at the conclusion of each flight. A consumption history log provides valuable information, both for future flight planning and for discerning engine performance trends.
When planning a cross-country flight, the objectives are to arrive at the planned destination safely with a reasonable reserve of fuel in hand and without affecting the safety of others while en route; or even creating a possibility that safety might be affected. But remember the first rule of aviation — fly the aeroplane at all times, navigate when able and always be a few minutes ahead of the aeroplane. When navigating a light aircraft, and particularly an open-cockpit ultralight, a person's capacity for mental arithmetic is not as good as it is when sitting at home. Nor is it easy, or maybe even possible, to manipulate navigation tools in flight and it is very difficult to handle charts, pencils and notepads in the cockpit. Pre-flight preparation should be directed towards reducing and simplifying the in-flight work load.
You should have a good acquaintance with the flight envelope of the aircraft, both with and without a passenger. In particular you must know the optimum cruise speeds obtained when cruising at, say, 75% power plus the proven fuel consumption, in litres per hour — at that throttle setting and aircraft weight. Calculate the maximum sector time allowable by dividing the total usable fuel capacity by the hourly consumption to find hours; then deduct 30 minutes reserve fuel to arrive at the maximum advisable sector time. For example let's say our aircraft has a fuel capacity of 66 litres with 64 litres usable; proven consumption at 70 knots normal cruise is 16 litres/hour. Then maximum sector time is 64/16 = 4.0 hours or 240 minutes; less 30 minutes fuel reserve = 210 minutes. Never equate fuel consumption with distance, only time.
Light aircraft consume 40% or 50% more fuel in a maximum power climb than at a normal cruise setting. It is normal practice to initially climb away at best rate of climb speed (Vy) until a safe height is reached, then airspeed is allowed to increase to a suitable en route climb speed, while maintaining maximum allowed climb power, until the cruise altitude is reached. The extra fuel consumption during the climb can be estimated from the normal rate of climb achieved. For example, rate of en route climb 250 feet/minute = four minutes per 1000 feet, then extra fuel consumed (~50%) is two minutes fuel per 1000 feet climbed. This extra fuel will be used whatever power setting is used in the climb; it is the chemical energy exchanged for the potential energy of height.
There are several articles in the online version of CASA's magazine Flight Safety Australia that are recommended reading. Look under 'Fuel management' in our categorised index of the articles of particular interest to recreational pilots in Flight Safety Australia.
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R/T communications and procedures in the 'VHF radiocommunications guide'.
All other civilian airfields can be classified as public or private. Public airfields are usually owned by the local government body and landing permission is generally not required, although it is always wise to check. Private airfields usually cannot be used without prior permission from the owner, except in an emergency — even then there may be problems with trespass. Landing and parking charges apply at many airfields.
There is much to be considered when planning a landing at an unfamiliar airfield, or indeed a familiar airfield. Please read 'Operations at non-controlled airfields' and 'Safety during take-off and landing'. The current ERSA should be fully consulted; particularly check the circuit procedures, stated hazards and whether the airfield is certified or registered, thus requiring use of VHF radio.
If the airfield is not shown in ERSA it will be a small private operation (an 'aircraft landing area' [ALA]) — possibly with a listing in the Australian Aircraft Owners and Pilots Association publication 'Airfield Directory', which has details of about 2000 airfields, including whether prior landing permission is required. If an airfield is not listed in ERSA or the AOPA Airfield Directory, then it is most unwise to contemplate using it without contacting the owner. Even if landing permission is not required, you should always pre-check with the owner/operator about hazards and conditions. It is too late to find out if the surface has been softened by rain when you are up to the axles and about to tip over.
Using a Google Earth image — found by the location latitude and longitude coordinates — may be a useful source of visual information for airstrips that don't appear in ERSA.
HazardsYou must be aware of your aircraft's landing (and subsequent take-off) performance in normal, soft field and short field conditions. You must also perform a safety audit of the destination and alternate airfields for length, slope, surface condition (e.g. roughness, mud, surface water), approach and go-around hazards, stock and wildlife hazards, tyre puncture and wheel hazards, and any commonly occurring micro-meteorological and dust hazards. Check runway directions and expected wind conditions, and be wary of airfields with single runways; crosswind conditions may be beyond your aircraft's capability. Be particularly wary of airfields with 'one-way' strips — they are extremely tricky, if not outright dangerous, for those not familiar with any topographic turbulence, sink or other atmospheric hazards that could exist. Low-lying strips may be badly softened by rain or inundation. The availability and location of suitable fuel should be checked. Remember, just because your assessment concludes that you can safely land at a particular airfield it does not guarantee that you will be able to take-off safely.
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Route construction is often done the day before planned departure, or even earlier if an extensive cross-country flight is planned.
With a soft pencil and a rule, draw a preliminary line on the chart between your departure and destination — you may have to overlap charts, but be aware that WAC and VNC are at different scales. Check along the line for areas to be avoided; i.e. 'tiger country' — rough, forested or hilly areas where there is a limited availability of open, cleared, flat land for an emergency landing. If possible, avoid long stretches of featureless terrain and also terrain exceeding 3500 feet elevation. If you are using a WAC, check the relevant ERC-L for CTR, PRD and CTAF aerodromes and mark them on the WAC. Note any other airfields near the line. Now decide which areas of terrain to avoid and find a suitable diversion around them. If that diversion takes you quite a distance from the direct line then so be it; it won't make that much difference to the total distance flown. If there are areas of scenic or other interest evident on the chart, you might plan to overfly them — even if it does makes a zigzag path.
Tracking around and beneath controlled airspaceIf your intended track is within the area covered by a VTC you must examine the current VTC for the mandated VFR routes for aircraft flying in Class G and plan to follow those routes. They are indicated as a line of large purple dots. Carefully check the VTC and current ERSA for the altitude at which these routes should be flown. You may find, for instance, that some coastal routes require flight in one direction at 500 feet amsl and at 1000 feet for the opposite direction. The Airservices Australia Flying Guides and Publications contains a lot of information to assist in planning flights around Sydney, Melbourne, Brisbane, Canberra, Adelaide and Perth to avoid violations of controlled airspace; look for the link to 'Visual guides'.
Note that on VTCs any area where the elevation does not provide at least 500 feet clearance between the terrain and the lower limit of the overlying CTA is tinted purple; such areas must be avoided. You may also find that when threading your way around CTRs, the clearance between the terrain and the overlying CTA may be so limited that all aircraft in Class G would be flying at much the same low height and tracking over the same ground, — this provides the conditions for a mid-air collision. Also in such terrain there is a significant possibility of strong lee downflows. Never plan to fly such routes unless a reasonable visibility is forecast and the winds around 3000 feet amsl are below 20 knots.
The Australian Transport Safety Bureau Web site contains a research report in PDF format Limitations of the See-and-Avoid Principle, which is recommended reading.
When planning to track near a CTR be aware that you must apply a tracking tolerance — offsetting it at least one nautical mile from the boundary of controlled airspace — if flight is planned below 2000 feet agl, or two nautical miles if between 2000 and 5000 feet agl; watch out for the overlaid CTA steps. A VHF radio is advisable when planning to operate close to a CTR because it is good airmanship to let them know you are there — if a heavy RPT aircraft is being let down overhead there is always a chance of being caught in sinking wake turbulence. Also if you do get caught between rising terrain and a lowering cloud base you can always call Air Traffic Control and inform them that you "require entry" to pass through the edge of the CTR because of deteriorating weather. ATC are always very helpful but unauthorised entry into the CTA or CTR (the dreaded 'violation of controlled airspace' or VCA) is a safety hazard and may earn a substantial fine. Read the article 'Lost in controlled airspace' in the online version of CASA's magazine Flight Safety Australia: November - December 2001 issue.
Waypoint selectionYou need to find readily recognisable point locations or waypoints for monitoring flight progress and/or to mark the points of diversion and consequent turning points. Suitable waypoints are airfields with formed runways, major road junctions, small towns, grain silos near rail lines, intersecting line features and distinctive permanent water features — though in drought conditions such features may not be obvious. You may also see some highly visible linear features — roads, railways, rivers, beaches — that roughly parallel your intended track for a reasonable distance. Plan a track divergence to intercept and then follow such line features — and be aware of the 'Rules of the Road' that require aircraft to track to the right of a line feature, or when flying within a valley or any air traffic lane. In the more remote areas of Australia the distances between verifiable landmarks are great and in such cases the only viable route is to follow sealed roads. Mark all the turning points on the chart, joining them to form the route segments of the required track. These turning points will also be used as fuel consumption checkpoints. Generally speaking, a route that provides the best visual fixes and reasonably short segments is the best option.
Measure the total track distance using the scale (in nautical miles) printed on the map or alternatively use the latitude graticule printed along the meridians; each mark is one minute of latitude or one nautical mile. The printed scale is easier to read and thus less prone to errors. (You can buy a ruler scaled in nautical miles for use with WACs, VNCs and VTCs online from the Airservices Australia online store navigation and planning accessories — and buy a protractor at the same time. ) Divide the total track distance by the cruise speed to get an approximate total time required. If the total time required is greater than the known maximum sector time, then the flight must be broken into two or more sectors by introducing refuelling stops at appropriate distances. This probably necessitates replanning the waypoints so that one or more coincide with an airfield with assured and suitable fuel supplies. Re-plot the route if necessary.
If the total time required is less than the maximum sector time, then the first-cut plan for the route to be followed may be viable — but we have not yet taken into account the effects of wind, which may be considerable; these are covered in the next module. Forecast weather and winds should be ascertained as close to the planned departure time as possible, but it is advisable to obtain a preliminary weather forecast the evening before the flight. If a very long flight is planned it is advisable to watch the weather patterns for a few days prior to the trip. Any NOTAM applicable to the area in which you intend to operate should also be obtained at that time. See section 3.6.
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(A larger 141 kb plot image is available. It will open in a new browser window.)
The chosen route utilises the 100 nm of low (elevation about 300 feet amsl) country, extending eastward from the departure airstrip where atmospheric conditions are likely to be less turbulent, with an east-west railway as a good line reference. There are two sentinel hills (Warraway Mountain) south of the rail line and about 75 nm east of Oxford that will provide a distinctive landmark for a turning point. The elevations shown are 895 and 987 feet, thus rising about 600 feet above the surrounding plain. All elevations on the WAC are in feet. We also note that there are two good alternate airfields in the vicinity, Lake Cargelligo and Condobolin, and find that the latter is 58 nm east of Warraway Mountain while Lake Cargelligo is 20 nm south-east of that hill (off the map image). Checking ERC-L(5) we find there is no special use airspace — restricted or danger areas — in the vicinity of our planned operation.
About 50 nm north-east of Warraway Mountain and at the top of the watershed is a distinctive road junction, suitable for the second waypoint. Note the figure 1584 in bold type, just above the road junction — this indicates the highest elevation (Mt Susannah) in that WAC grid section. Similarly the figure 1528 just to the right of the junction indicates the location of the highest elevation in the neighbouring grid section. Thus we will have good indication of track holding from quite a distance if we appear to be tracking towards a position midway between those high points. Also there is a road about 20 nm north-east of Warraway Mountain, which we will cross at right angles, to provide a good ground speed check.
The last segment is a 30 nm run following the valley downslope direct to Tottenham, which, from ERSA, has an elevation of 780 feet. There is a cautionary note in ERSA that a significant animal hazard (kangaroos?) exists on the airfield. Tottenham should be readily recognised from a distance by the distinctive pattern of minor roads, the rail line coming from the south-east and terminating at Tottenham, plus the mine (indicated by the crossed pick and hammer symbol) and a large grain silo. The symbol for the latter is difficult to see but it is right against the western edge of the purple circle indicating the airfield. The total distance of the three route segments is about 155 nm, very little more than the straight line route and much easier pilotage.
The approximate sector time will be 155 divided by our 70 knot cruise = 2.2 hours or 132 minutes, well within our maximum sector time of 210 minutes. Thus the flight will be viable — if the weather is favourable.
Checking ERC-L(5) the relevant Melbourne FIS communications frequencies are ML 124.9 for the first two legs and ML 123.9 for the final.
Quantifying the route dataWe can now measure the non-variable route segment data to initiate the flight plan:
• Centre the protractor on Oxford, ensure that the protractor is aligned with the chart meridians and read off the bearing to the first waypoint — about 094° true.
• Centre the protractor on Warraway Mountain and read off the bearing to the second waypoint — about 061° true.
• Centre the protractor on the road junction and read off the bearing to Tottenham — about 040° true.
• Note that you can use the face of the protractor shown on the left as an erasable drawing surface.
• Using a scale ruler to measure the length of each route segment we find they are 74, 52 and 33 nm respectively.
Checking minimum safe altitudeWe now have to decide the minimum altitude at which each segment can be safely flown. We will allow a minimum safety margin of about 1000 feet above the highest terrain 10 nm either side of the required track. From the chart the highest terrain for the first segment is 1036 feet, so our lowest safe altitude is 2000 feet above mean sea level. Similarly on the second and third legs the highest terrain is 1584 feet, so our lowest safe altitude will be 2500 feet on both. The cruising altitude will be determined by the wind profile at flight time and the appropriate VFR cruising level; although for best engine performance a cruise altitude, where the throttle is fully open and the engine is delivering 65%–75% power, is indicated.
The preliminary flight planWe have now accumulated the non-variable part of our flight plan:
Before we can proceed further we must:
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Airservices Australia provides an online forecast service for 30 or so aviation forecast areas — ARFORs — shown on the PCA. First we need to locate our flight area on the PCA — outlined in green on the PCA section shown and thus located in ARFOR 22.
The black grid on the PCA is the individual WAC coverage so our planned flight area (outlined in green) is more or less contained in WAC 3457 but we would certainly need to also take along WAC 3356 adjoining the northern edge of WAC 3457.
Meteorological information for any ARFOR can be obtained from Airservices Australia's internet meteorological briefing system www.airservices.gov.au/brief/aismet.asp. Just click 'Area Briefing' on the opening page, then the ARFOR area (in our case, 22) on the map display. Also place a check in the 'Head Office Notam — summary' request box but uncheck the other boxes. An area briefing provides area meteorological information, NOTAM and meteorological information on aerodromes, NOTAM for restricted areas within the selected area, and relevant Flight Information Region meteorological and NOTAM information. The aerodrome meteorological information is in the form of Meteorological Reports [METAR] and Aerodrome Forecasts [TAF]. We will look at the meteorological information in the flight plan preparation module for which I have downloaded an area 22 ARFOR and added some comments (this opens in a new browser window).
Plain English conversions of current ARFOR, METAR and TAF for all Australian ARFOR areas are available from Ian Boag's website. However pilots must still get the NOTAM from the Airservices site. Also student pilots should be aware that the ability to decode the BOM information will be tested in some of the aviation examinations.
(Bear in mind that CAR 120 imposes penalties for use of forecasts that were not made with the authority of the Director of Meteorology and it may be that plain English conversions are not authorised by the Director.)
The times of first light and last light for any Australian location can also be accessed from the opening page — click 'First light / Last light' (or go direct to www.airservices.gov.au/brief/lightbrf.asp) and follow the instructions.
You can also download the current and forecast national weather charts (plus a great deal of other information) from the Australian Bureau of Meteorology website aviation weather services page.
Go to www.bom.gov.au/reguser/by_prod/aviation/.
From that page you can also access the images from the Australian Weather Watch Radar Network. The colour images indicate the intensity of atmospheric precipitation overlaid on a surface map for an area up to 512 km radius from the radar. The radar images are updated every 10 minutes or so and the latest four images can be rolled into a progressive display that gives an indication of the development and velocity of such weather phenomena. The weather radars provide the most accurate and up-to-date rain and storm information, and should always be checked prior to a flight within areas covered by the radars.
UTCCoordinated Universal Time [UTC] and the 24-hour clock — rather than local time — are used throughout the flight information and meteorological services. UTC is 10 hours behind Australian Eastern Standard Time, 9.5 hours behind Australian Central Standard Time and 8 hours behind Australian Western Standard Time. Add an additional hour in a daylight saving time period. You can check current UTC on the opening page of Airservices meteorological briefing system at www.airservices.gov.au/brief/aismet.asp; just click 'UTC Time'. UTC is often referred to as 'Zulu' time because it is normally distinguished by the suffix 'Z' and Zulu is the standard phonetic for that letter.
NAIPSAirservices Australia also provides the National Aeronautical Information Processing System [NAIPS], a user-friendly and comprehensive online pilot briefing and flight notification service. Further information is contained in the 'Electronic planning and navigation' module.
The next module deals with the effect of wind on our flight plan.
|Stuff you don't need to know
• DR was born in the early days of oceanic sailing vessels. Every hour or two during the voyage the log (a quadrant shaped piece of wood weighted to float upright with an attached log-line knotted at intervals) was dropped over the stern of a vessel under way and the vessel's speed was reckoned from the amount of line paid out over a particular period of time. In 1637 an English mathematician and navigator, Richard Norwood, calculated that the spacing between knots should be 47.25 feet with a 28 second sand glass used as the timer. If you do the calculation, using the then estimated 6075 feet to the nautical mile, you will see that the number of knots that passed over the stern rail during the 28 second period equals the ship's speed in nautical miles per hour — hence knots. The log was presumed to be 'dead in the water'; i.e not dragged by the ship or affected by tide, drift or current. Each reading was marked on a log-slate and, during each watch, the course, speed and distance reckonings — adjusted for tide and current estimates — were entered in the logbook.
(Note: some obviously non-nautical people reckon that 'dead reckoning' is a diminutive of 'deduced' reckoning, but I reckon their reckoning is wrong. According to the Oxford English Dictionary the term 'dead reckoning' first appeared in print in 1613 in a work titled 'Magnetic Bodies' written by one M. Ridley; so the term has been in use for at least four centuries. The term also appeared in Richard Norwood's work, The Seaman's Practice, published in 1637.)
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Groundschool — Flight Planning & Navigation Guide
|Module 4 of the Flight Planning & Navigation Guide discusses the effects of wind on heading and groundspeed|
Copyright © 2001–2009 John Brandon [contact information]