Originally Posted by bubbers44
It was difficult to know exactly what IAS would do flying a FL and flying into colder air because the mach would increase because of the colder air and the speed of sound would of course decrease but how much, if any, would this change the IAS? Also would the true altitude change?
Well, suppose you have a constant true altitude - say, sea level - and the temperature changes, for example from +40 to -40 while the pressure remains unchanged...
If pressure is not changed, flight level is not changed. But the density of air changes. Therefore the IAS changes at a constant TAS.
Right?
So, the same ought to apply at any higher FL... as the FL follows pressure, flying into colder air should increase IAS if the TAS is unchanged...