temp correction
doubleoh:
I would agree that Canada provides the correct information.
RYR-738-JOCKEY:
Should have said "correct", not "corrected".
QFE is the reference, and QNH is computed based on ISA, and when the temperatre is different the errors appear. Also rememebr in mountainous terrain, the error can be of a large magnitude.
It is perfectly possible for a modern ADC to compensate, as it knows the actual temperatre, at all times, (less any computation lag), thus a corrected height could be displayed. However the lag at normal appraoch speds would be unacceptable.
Arctaurus:
At -53C at a sea level airport you are about 100ft below your displayed altitude, so the baro shows 200ft (cat 1), but you are at 100 (cat 2). The rad alt will show the correct height.
But remember, on a cat 1 approach the RAD alt is not the approved height measuring device.
I have been working in Siberia this winter, and these errors are noticable. BUT in Russia you land on QFE, so no problem.
Bumz