PPL air law question QNH & QFE
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PPL air law question QNH & QFE
Hi,
I have my air law exam next week and im totally stuck on one type of question! Ive used the search funtion but with no success
Please help
The question is...
You are setting your altimeter at an aerodrome, where the elevation is -31 ft. The QNH you have been given is 1029 millibars. What would you expect the aerodrome QFE to be?
A 1015 millibars
B 1030 millibars
C 1028 millibars
D 1032 millibars
How would you work this out??
Thanks alot for any help in advance and hope this is the right section to put it in.
Cheers
Conk
I have my air law exam next week and im totally stuck on one type of question! Ive used the search funtion but with no success
Please help
The question is...
You are setting your altimeter at an aerodrome, where the elevation is -31 ft. The QNH you have been given is 1029 millibars. What would you expect the aerodrome QFE to be?
A 1015 millibars
B 1030 millibars
C 1028 millibars
D 1032 millibars
How would you work this out??
Thanks alot for any help in advance and hope this is the right section to put it in.
Cheers
Conk
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Quick revision of the basics;
QNH - the pressure you set on your altimeter subscale that will result in the altitude being displayed as feet above mean sea level.
QFE - the pressure you set on your altimeter subscale that will result in the height being displayed as feet above aerodrome datum.
In a standard atmosphere the pressure decreases by 1mb (or 1HPa) for an increase in height of approximately 30 feet.
Thus at an airfield with an elevation of 330 feet above sea level the QFE will be 11mb lower than the QNH.
To answer your question - your airfield elevation is -31 feet, therefore the QFE will be 1mb higher than the QNH of 1029mb - ie 1030mb, answer B.
HTH
QNH - the pressure you set on your altimeter subscale that will result in the altitude being displayed as feet above mean sea level.
QFE - the pressure you set on your altimeter subscale that will result in the height being displayed as feet above aerodrome datum.
In a standard atmosphere the pressure decreases by 1mb (or 1HPa) for an increase in height of approximately 30 feet.
Thus at an airfield with an elevation of 330 feet above sea level the QFE will be 11mb lower than the QNH.
To answer your question - your airfield elevation is -31 feet, therefore the QFE will be 1mb higher than the QNH of 1029mb - ie 1030mb, answer B.
HTH
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rule of thumb 1mb = 30ft so id go for 1030mb.This is because you lose approx 1mb per 30ft in height you gain.
Almost the same type of questions appear in MET too..
Liam
Almost the same type of questions appear in MET too..
Liam
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Below sea level and QFE will be greater than QNH. Not many airports are actually below sea level!!
If you set your altimeter subscale such that the "altitude" is zero, the setting should be equivalent to the QFE. Do the same for the airfield elevation, and the setting will read the QNH.
Cheers
Whirls
PS edit - Air Soul's excplanation is more accurate but I fly from Norfolk where there's v. little difference!!
If you set your altimeter subscale such that the "altitude" is zero, the setting should be equivalent to the QFE. Do the same for the airfield elevation, and the setting will read the QNH.
Cheers
Whirls
PS edit - Air Soul's excplanation is more accurate but I fly from Norfolk where there's v. little difference!!
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Anybody spot air soul's deliberate mistook?
Cusco
Cusco
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Thanks fore the replys
According to air quiz the answer was B
Could some please post a formula up because im still struggling?
Im fine with questions like...
You are approaching an aerodrome at an altitude of 1230 ft, with QNH 1015 millibars set. You set 987 millibars QFE for landing. What will your altimeter read now?
Is it along the same principles?
Conk
According to air quiz the answer was B
Could some please post a formula up because im still struggling?
Im fine with questions like...
You are approaching an aerodrome at an altitude of 1230 ft, with QNH 1015 millibars set. You set 987 millibars QFE for landing. What will your altimeter read now?
Is it along the same principles?
Conk
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conk, the formula is the same you have been using. You just need to do what Pitts forgot to do and read the question properly!
The aerodrome was MINUS 31 feet which puts BELOW sea level. In this case the QNH was going to be lower than the QFE or put it another way the sea level was above the airfield so you are going to add rather than deduct.
QNH = 1029
Airfield Elevation is 31ft so 1mb BUT it is a NEGATIVE elevation so
1029 +1 = 1030
If it was a postive elevation then it would be 1028
There are a few negative elevation airfields around, I seem to recall Texel may be.
The aerodrome was MINUS 31 feet which puts BELOW sea level. In this case the QNH was going to be lower than the QFE or put it another way the sea level was above the airfield so you are going to add rather than deduct.
QNH = 1029
Airfield Elevation is 31ft so 1mb BUT it is a NEGATIVE elevation so
1029 +1 = 1030
If it was a postive elevation then it would be 1028
There are a few negative elevation airfields around, I seem to recall Texel may be.
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I dislike questions like this. It's a trick question really as in over 20 years and 12,000 hours of flying, I have never landed at an airport below sea level ones.
(Some of the sea level ones were slightly lower after my landing, but not before - old aviation joke).
(Some of the sea level ones were slightly lower after my landing, but not before - old aviation joke).
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There are a few negative elevation airfields around, I seem to recall Texel may be.
I have landed at Schiphol many times and I seem to recall it is minus 11ft.
But in the Netherlands we don't do QFE, just QNH so it's all a bit of a non-issue.
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When I landed at Furnace Creek (Death Valley National Park Ca. -210ft) a coupla years ago, even though I knew it was below sealevel and by how much, the altimeter readings so spooked me on final that I threw the approach away, went around and sorted myself out: second circuit = perfect landing.
Cusco
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exam advice
You just need to do what Pitts forgot to do and read the question properly
R.T.F.Q = (at least) 1/2 T.F.A
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You are approaching an aerodrome at an altitude of 1230 ft, with QNH 1015 millibars set. You set 987 millibars QFE for landing. What will your altimeter read now?
810ft?
Got my Airlaw in the next 2 weeks, bloody dreading it. This QNH & QFE throws me too.
810ft?
Got my Airlaw in the next 2 weeks, bloody dreading it. This QNH & QFE throws me too.
Last edited by BladeM3; 17th Nov 2008 at 12:41.