View Full Version : Temperature Error Correction Question (Cathay Book)

Lafyar Cokov
12th Feb 2008, 23:44
Ok - I am now stumped - there is the following question in the Cathay Book:

On a 3 glide path, OAT -25, OM crossing height of 1760', the aircraft altitude will indicate:

a. 1820'
b. 1760'
c. 1720'

The answer given is A. I agree that the answer must be higher than the indicated but using the standard (approximate) temp error calculation I reach:
(Assuming Gnd OAT = -21C)
4 * (21+15) * 1.8 = 4 * 36 * 1.8 = 259.2ft

Therefore answer is about 2020ft

Am I massively wrong or is the question out???


Bruce Waddington
13th Feb 2008, 05:16

You calculations are good. The chart we use at our airline produces a correction of 280 feet. This would give an indicated altitude of 2040 when crossing the outer marker on the glide slope.

I worked the correction out for an airport elevation of 0 feet.

best regards,

Bruce Waddington

13th Feb 2008, 10:29
Could it be a misprint - if the temp was +25, then wouldn't 'c' be right?

13th Feb 2008, 11:30
Lateral thinking indeed:) but "The answer given is A.":confused:

21st Feb 2008, 17:46
The exact answer is irrelavent and impossible to know without knowing the elevation of the airfield, they just want you to pick the only answer that is higher than the published crossing alt. to show you understand how cold weather affects the altimeter. It can only be A.


21st Feb 2008, 20:33
Yep, I agree with Bengolds..;and not to mention..but a few other infos are missing..anyway the reading must be higher than the one published..and so for..the only one acceptable is the "A"..

As mentioned, they only want a check your understanding about the influence of the actual T...

You're quite lucky..It coulld have been:

a: 1765
b: 1780
c: 1835


21st Feb 2008, 21:30
Hot to Cold don`t be bold...:}