ATPL Met question
Thread Starter
Joined: Aug 2010
Posts: 23
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From: Aberdeen
ATPL Met question
Hi everyone,
Im studying my ATPL's at the moment however iv come across a question that has me banging my head of the wall. The question states
The altimiter of an Aircraft at FL40 is corrected for pressure error giving an indicated altitude of 3892ft. if the temp is ISA -12, what is the true altitude?
The answer they have come up with is 3705ft.
However I have NO IDEA how they came up with it.
If anyone could shed some more light on how they got the answer it would be very appreciated.
Im studying my ATPL's at the moment however iv come across a question that has me banging my head of the wall. The question states
The altimiter of an Aircraft at FL40 is corrected for pressure error giving an indicated altitude of 3892ft. if the temp is ISA -12, what is the true altitude?
The answer they have come up with is 3705ft.
However I have NO IDEA how they came up with it.
If anyone could shed some more light on how they got the answer it would be very appreciated.
Joined: Jan 2011
Posts: 660
Likes: 20
From: England
For non ISA temperatures use a correction of
4 feet per degree ISA deviation per 1000 feet
Inserting the figures in youir question gives a correction of
4 x (-12) x 3.892 = -186.816
Adding this correction to your indicated altitude gives
True alt = 3892 - 186.816 = 3705.184 feet
4 feet per degree ISA deviation per 1000 feet
Inserting the figures in youir question gives a correction of
4 x (-12) x 3.892 = -186.816
Adding this correction to your indicated altitude gives
True alt = 3892 - 186.816 = 3705.184 feet
Joined: Jan 2011
Posts: 660
Likes: 20
From: England
Yes, we have a correction factor of 4 feet per 1000 feet per degrees ISA deviation, so if our indicated alt is in feet we need to convert it into thousands of feet (by dividing by 1000).
3892 / 1000 = 3.892
3892 / 1000 = 3.892
