Mon Apr 08, 2019 12:37 pm
Sorry, but when flying into hotter air the altimeter will under-read, not over-read.
Think of the atmosphere as a set of surfaces, each corresponding to a given absolute pressure. Those surfaces will rise and fall like contours according to temperature - in cold air they will be compressed closer together, in warmer air they will stretch out further apart.
As you travel along at a given pressure setting on your altimeter, maintaining a constant indicated altitude, you are flying along one of those contours. If you pass into warmer air you will follow that contour upwards; i.e. your true altitude will increase while your indicated altitude remains the same - your altimeter will therefore under-read. Similarly, if you pass into colder air, the contours become compressed and you will descend while indicating a constant altitude - your altimeter will over-read. This is addition to any change in local QNH which in itself would move the datum up and down if not corrected.
As in pressure settings varying as you travel enroute 'High to Low - Beware Below'
Sent from my high horse not using Tapatalk