Air Law exam on Saturday

[PompeyPaul]

Qfe & Qnh

I understand the differences between QFE & QNH but I don't understand how you convert heights between the two pressure scales, like this question:

Your aerodrome elevation is 24 ft, and the QFE you have just been given is 1021 millibars. What would you expect the aerodrome QNH to be?
A 1015 millibars
B 1020 millibars
C 1022 millibars
D 1027 millibars

There must be some mapping between the 2, but I just don't get it. Somehow I have to work out what the pressure difference is across 24ft and add it to 1021. Anyone ?

[PompeyPaul]

Qfe & Qnh

I understand the differences between QFE & QNH. I don't understand how you map one to the other though, i.e.

Your aerodrome elevation is 24 ft, and the QFE you have just been given is 1021 millibars. What would you expect the aerodrome QNH to be?
A 1015 millibars
B 1020 millibars
C 1022 millibars
D 1027 millibars

Obviously I need to work out the pressure difference 24ft makes and add it to 1021 to get the result. Is there some constant mapping per foot of pressure ? Anyone ?

Thanks

[Merritt]

You will be pleased to know its very easy.

Pressure drops as you get higher by approx 1mb per 30ft

so if your QNH is 1000mb (at MSL), your QFE at 30ft would be 999mb....


HTH

Steve

[PompeyPaul]

Thanks for all of the help folks

I PASSED!!!!

Ouch my head hurts today.

[tiggermoth]

Paul,

Well done !

[BigAl's]

Originally Posted by PompeyPaul

I understand the differences between QFE & QNH. I don't understand how you map one to the other though, i.e.

Your aerodrome elevation is 24 ft, and the QFE you have just been given is 1021 millibars. What would you expect the aerodrome QNH to be?
A 1015 millibars
B 1020 millibars
C 1022 millibars
D 1027 millibars

Obviously I need to work out the pressure difference 24ft makes and add it to 1021 to get the result. Is there some constant mapping per foot of pressure ? Anyone ?

Thanks

So in this instance the answer is C.. 1022. As has been said, pressure drops with altitude gained. Given that 1mb = 30ft, QFE at MSL (and hebce QNH) would be 1022, (24ft lower giving an increase of approx 1mb).

I'm pretty sure that's right!.. I hope. It is past my bed time!

Well done on the exam pass!!

[Nil Flaps]

Good work fella

On yer Paulie!

[Captain Smithy]

Well done Paul! Great to hear you did it.