Altimeter adjustment

[facthunter]

I think it varies Turbo.

 

Setting aerodrome height on your altimeter is a good start. The aerodrome is not always level so there should be a reference point, where you set it.

 

2 things then require you to to reset it. (The datum on the Kollsman scale).. One relates to moving across the countryside and the other relates to the weather systems moving across the countryside. You then need a current area QNH to reset it to. This could be from a forecast that you have or receiving the appropriate figure from ATC.. IF your altimeter is not calibrated all this is academic..

 

To check the altimeter have a current area QNH on the subscale and be at an aerodrome that you know the height of. Your instrument should read the actual aerodrome height.. There is a tolerance . If you are outside it your altimeter is technically unserviceable. Nev

 

 

[jakej]

"To check the altimeter have a current area QNH on the subscale and be at an aerodrome that you know the height of. Your instrument should read the actual aerodrome height.. There is a tolerance . If you are outside it your altimeter is technically unserviceable. Nev"

 

"VFR altimeters have a +/- 100' tolerance to be legal." cficare

 

Wasn't this covered in post #6 ?

 

 

[facthunter]

I attempted a summary Jake. And to put some of it in different words. If I repeat what you have said in part of it then I am obviously agreeing with you.

 

Going to Yenn's point, when there are regular traffic going in and out of an aerodrome as well as allowing more height, try not to tangle with the other traffic on climb or descent into the aerodrome..Stay off their track. ( If known). Nev.

 

 

[jakej]

Yeah I know Nev It just seemed an inordinate amount of 'traffic' to get a basic point across. Pardon my ignorance but isn't basic Altimetry (& Radio too) taught to RA Aus pilots ? If not then there are more potential problems with some ops to below 10,000 ft, no ?

 

 

[Jabiru Phil]

I record data about each waypoint (including aerodromes) on my flight plan knee board sheet. It includes AD name, ICAO designation, CTAF, Area freq, Altitude (and any other notes like right hand circuit, runway numbers, PAL, etc..)That way, I just glance at the sheet to instantly mentally calculate what altitude I need to be, for what I'm doing. After turning Base, I don't look at the altimeter anymore. I just look at the aerodrome and runway, pick an aiming point and continue to adjust glide slope as required by the prevailing wind, wind shear etc.. I do sometimes glance at altitude as I turn final, but it isn't something I have any fixation about. Can't use that for a simulated engine failure or a pitch and recover landing.

 

Jabiru Phil;

 

Just wondering what it means to have an altitude for Base and Final? We turn Base from circuit altitude, and then descend from there until you land. The only fixed points at which you might register altitude would be joining downwind (at circuit height) and turning final (at a height specific to your aircraft and circuit size).

David 10

 

Guess that it sounds confusing using the 800' on base but this allows me to on average be on final at 500'

 

Perhaps you more experience pilots can do this with eyes shut. Same could be said for balance ball, I rarely have to monitor now except glances when landing, where once I used to watch constantly.

 

 

[jakej]

David

 

Not meant to be critical, more like stunned about the lack of understanding. Contributing to the knowledge base is what I also do, encourage, and will continue to do so however shouldn't Altimetry be part of the training syllabus ?

 

 

[jakej]

I hear you.

 

 

[Guest davidh10]

Jake;

 

It is also possible for students to learn what to do, but not understand why. Some are satisfied with that level of knowledge, but others ask questions to seek an understanding. That's good.

 

There are a variety of ways in which we learn, but each person has a key modality that is best for them. The fact that we all respond in different ways to a question, plays to that need.

 

 

[petetheprinta]

My Fault, I asked what I thought was a simple hypothetical question on procedure, I have been taught not to alter my altimeter, it was a question as to why not, and suddenly we are onto the merits or not of RAA instructors, schools and what ever else. My previous question got locked out by IAN coz of people getting totally off subject and obviously getting very irate with one and other on the pros and cons of the Jabiru.. Give me a break fellas, all I ask is stay on topic please.

 

 

[jakej]

Correct David, no offense meant Pete.:big_grin:

 

My real concern is that some Instructors may not be making sure that pilots understand the theory taught as distinct from just hearing. I know of a situation where I questioned a pilot about how he used his altimeter - his reply was that he just dialed in aerodrome elevation, no problem with that except the altimeter was reading - 800 ft, I was stunned then too.

 

So Pete ,and others, please ask the questions as we are here to help and learn.

 

Jake J

 

 

[petetheprinta]

Thanks David and Jake, no offence taken. I have a lot to learn and a million questions, so be warned.

 

 

[jakej]

Thanks David and Jake, no offence taken. I have a lot to learn and a million questions, so be warned.

Check your pm - I have a question, totally unrelated but more about UHFs.

 

 

[Bryon]

"We really have a lot to contribute in the right spirit and we can learn from the experience as well, after all we are not always right"

 

David Isaac, post #40

 

I agree David, I once thought I was wrong, ..........................but I was mistaken

 

 

[Guest davidh10]

As an example of how pressure and thus altitude reading can change quite quickly, even in a "local area", this was from yesterday. Altimeter duly adjusted for aerodrome elevation at 420' just prior to takeoff roll. On landing two hours later on the same runway, it read 520'.

 

That means that for me circuit height was in fact 100' lower, as flown, to land compared with someone who had just taken off to do circuits.

 

 

[Louis Moore]

Hey Pete,

 

Took me reading this a few times but I get the point know, your purely talking about reducing your work load. I agree with David, (by the way AD refers to Aerodrome) leaving the QNH set on the altimeter to display your altitude AMSL means your altimeter will theoretically display what any other aircraft in the vicinities altimeter will be displaying and thus make it easy to maintain separation.

 

As others have already said re-adjusting your altimeter during flight I would think would increase your work load more than simply adding a 1000 ft to airport elevation. It is worthwhile noting that you are allowed to "round up and down" the airfield elevation to whole numbers to make it easier, I do!!!! So if the airfield elevation is 1258 ft I simply add 1000ft to 1300ft, making my circuit height 2300ft. I tend to forget about my height once I turn base and just look at the runway for a guide. In time you will find yourself not worrying about all 500ft marks.

 

 

[J170 Owner]

It's part of the flight plan Peter. Disregarding air pressure changes, if you plan a flight to (say) Chinchilla, you look at ERSA and see that Chincilla has an ELEVATION of about 1000 feet. So you plan to arrive in the circuit at 2000 feet indicated on your altimeter. However, especially on a longer flight, the pressure may drop (say) 10 millibars. That's 300 feet, and a drop in pressure means you will be flying that 300 feet LOWER in order to get the desired 2000 feet reading. You will actually be 700 feet AGL at the destination. Remember, from HIGH to LOW, lookout below!!!!

 

 

[J170 Owner]

Just for the record, aerodromes have an elevation, not altitude.

 

 

[facthunter]

You are right. On the ERSA chart you will see ELEV shown. If a student asked me what that meant I would say it was the height of the aerodrome above ( or in rare circumstances below) mean sea level. Altimetry is not always understood by all and can easily be the cause of a catastrophe where someone gets the figure wrong in their mind, and thinks the aerodrome is at sea level when you are actually at Alice Springs, in the middle of the night. Some countries use QFE, which makes the altimeter be zero when it is at the aerodrome level/elevation/height. This might at first glance seem like a good idea except that it then reads meaningless altitudes at all other times. You couldn't use the readings to ensure clearance above terrain enroute, without doing mental gymnastics or have vertical separation from other traffic. To have this separation you have to have all altimeters in the same location based on the one QNH at any given time.

 

Another good one is to set the subscale out by 10 at transition level. ie 1003 instead of 1013. This gives about a 300' error. Enough to put you at or below the ground at DH on an ILS approach. Nev

 

 

[Guest davidh10]

Just for the record, aerodromes have an elevation, not altitude.

Thanks J170. I've amended the term in my post to use the term in conventional use.

Having said that, it isn't actually incorrect, just unconventional. Either altitude or elevation could be used with respect to an aerodrome height above mean sea level, however only altitude can be used with respect to an airbourne object. Just for reference, the definitions from CAR 1988:-

 

• altitude means the vertical distance of a level or a point, or an
  object considered as a point, measured from mean sea level.
   
   
  
• elevation means the vertical distance of a point or a level on or
  affixed to the surface of the earth, measured from mean sea
  level.
   
   
  

 

 

The term "height" is not defined in CAR 1988, and thus must have a reference point specified when used, as for instance in "circuit height" being referenced to "AGL" (above ground level).

 

 

[skeptic36]

Hi all,

 

For anybody that is still unsure about QNH etc this thread is very comprehensive.

 

It makes me feel a little embarrassed reading it back now

 

Regards Bill

 

 

[facthunter]

Yes, I just read through that again 36,

 

ALL instructors/ teachers are aware of the need to assess the understanding of the information that their pupils should attain. The whole flying training thing, is skills assesment based. If the follow-up (assessment) is not done, the job is not finished. It seems pretty obvious that although some schools do it , well some aren't doing it well. We're talking Airmanship folks, not how to mix paint. Nev

 

 

[Guest davidh10]

Yes, I just read through that again 36,ALL instructors/ teachers are aware of the need to assess the understanding of the information that their pupils should attain. The whole flying training thing, is skills assesment based. If the follow-up (assessment) is not done, the job is not finished. It seems pretty obvious that although some schools do it , well some aren't doing it well. We're talking Airmanship folks, not how to mix paint. Nev

With the objective of not mixing paint ;-)

 

 

[Another David]

I am just learning to fly and doing circuits. So far I have flown from 3 different Airstrips at vastly different heights. While I can see the merit of setting the altimeter at the circuit elevation when venturing away from base to another airfield it makes no sense to me when taking off and landing and flying over the same place it can't be just left on 0 from the ground as in England. . All the approach heights are then easy to follow. There is something just wrong about landing and the altimeter reading 1500'

 

Also from reading all these threads from some obviously very experienced pilots going on about all the variables of altimeter settings based on pressure and the changing there of with weather mountains etc. Why in this day and age aren't all planes equiped with a GPS or Radar height calculator that would give the correct height without all the re setting.

 

 

[facthunter]

David, you don't fly actual heights, at the moment You use altimeters that are calibrated based on a STANDARD atmosphere and there is an assumption that they are serviceable and set to the correct baro figure. ( below transition height) You then fly a constant pressure height when over 10,000" when you go to a 1013 mb or Kpa datum . Aircaft performance can be better calculated with pressure height especially engine fuel consumption figures . vertical separation is catered for also. The time may come when GPS derived heights may be used. but don't hold your breath. Incidently half the world uses metric altimeters where height is shown in meters.. Life wasn't meant to be easy. Nev

 

 

[Guest davidh10]

...it makes no sense to me when taking off and landing and flying over the same place it can't be just left on 0 from the ground as in England. . All the approach heights are then easy to follow. There is something just wrong about landing and the altimeter reading 1500'....

You are only thinking about your reference in the statement above. How will you respond when an inbound aircraft queries your position? You have to give it in 3D. ie. usually a radial and distance from the aerodrome and an altitude, which is referenced to Mean Sea Level.

Now picture several aerodromes within say 10-20 miles of each other, and which have different elevations. At what point would you change your reference to another aerodrome, if your were referencing altitude to one of the aerodromes. Worse, how do aircraft approaching from different directions, and by your suggested standard of referencing altitude from aerodrome elevation, translate the altitude you give to that over the aerodrome to which they are closest? What a mess that would be. Hope that you can understand it now that the picture is a little more realistic, rather than just one inbound aircraft and one aerodrome, or you just doing circuits with other local aircraft.