QFE/QNH question

[vi1012]

Hey folks i have a question here i am struggling with, i came across a similar question on the forums but i am still kind of lost, help anyone??

At an airport, the QFE is 850mb and the QNH id 1010mb. An aircraft making an approach to land has its port altimeter set to QNH and starboard to QFE.
a- what is the elevation of the aerodrome?
b-what is the diff btween the 2 altimeters (i think i got this one)
c-what does the port alt read at 2000feet QFE?

THANKS......

[dan1165]

Field elev : 4480 '
Port alt set to QNH read 6480 'at 2000' QFE

[CAT3C AUTOLAND]

Always worth drawing a picture with Altimetry questions. That way you can see where the datums are.

Remember 1Hpa is equal to 28'.

[bingofuel]

I always thought 1 mb was equal to 27 ft at lower levels, does this mean 1 mb is not equal to 1 hectopascal after all ???

[Whirlygig]

Indeed ... I was taught 27' for CPL (30' for PPL but then that makes the maths easier).

Have standard atmospheres changed?

[pudoc]

Life's too short to worry about 1ft!

[Whirlygig]

Not when it comes between a resit of an exam at £70 a pop, it doesn't.

[pudoc]

Exams tend to have a little leeway between 27ft - 30ft per mb.

[SFI145]

I mb does = 1 hectopascal
The exact equivalent conversion to feet is given by
96T/P where T is in degrees K
So at sea level on an ISA day

1 hPa is equivalent to 96*288/1013 = 27.29 ft

[777-Aviator]

At an airport, the QFE is 850mb and the QNH id 1010mb. An aircraft making an approach to land has its port altimeter set to QNH and starboard to QFE.

a- what is the elevation of the aerodrome?

(QNH - QFE) * 27
Be diligent about it in the exam...If you try 27 and non of the answers provided is close enough to the answer you came up with, then try 28 or 30 in some cases (still applies to ATPL level!!)


b-what is the diff between the 2 altimeters (i think i got this one)

Well..in a conventional "ATPL-style" aircraft, they want you to believe that the port source supplies the LHS altimeter while the starboard source supplies the RHS altimeter. So in this question, the captain altimeter would read QNH (Altitude) while the co-pilot altimeter would read QFE (height above the airfield). On the ground, the Captain Altimeter would read the aerodrome elevation while the co-pilot altimeter would read ZERO.

c-what does the port alt read at 2000feet QFE?

The airfield elevation + 2000ft.


All the best mate.