Qfe & Qnh

[ben123]

Hi everyone, I was given given this question in a recent college assignment;

Q) If an altimeter millibar scale is set to QFE at one airfeild, and the aircraft flown to another airfield of the same height above sea level:-

a) The scale may need resetting before landing for the altimeter to read zero on landing
b) The scale will not need resetting for the altimeter to read zero on landing
c) The altimeter will read the height of the air field above sea level

To be honest i was hoping someone could give me the text book answer, as I think if the pressure did not change B could be correct, but of course it takes time to fly from one airfield to the next so the pressure could change. What do you do in practice?

Any help appreciated, Thankyou Ben

[Dufwer]

I would go for a). If the question had stated that the pressure at airfield B was the same as A, then you would not need to reset, but the question doesn't give that detail so you may need to reset. It is good airmanship to check upon arrival. c) is wrong because QFE is height above aerodrome level, not altitude above sea level.

D

[Dantruck]

Dufwer is correct. The answer is 'A'.
The keyword here is MAY...it may need resetting because the atmospheric pressure may be different at the other airfield.

Remember, an altimeter is a pressure instrument, ie: it senses (works off) air pressure which, like your investments, can go down as well as up.

Of course, an altimeter may even need to be reset if the aircraft is landing back at the same airfield. If the pressure changes while you're flying around enjoying yourself, the altimeter will think the airfield has risen or fallen when you return.

[ben123]

Thankyou for your help, I understand now..

[Dantruck]

Dufwer is correct. The answer is 'A'.
The keyword here is MAY...it may need resetting because the atmospheric pressure may be different at the other airfield.

Remember, an altimeter is a pressure instrument, ie: it senses (works off) air pressure which, like your investments, can go down as well as up.

Of course, an altimeter may even need to be reset if the aircraft is landing back at the same airfield. If the pressure changes while you're flying around enjoying yourself, the altimeter will think the airfield has risen or fallen when you return.