Originally Posted by
carlwag
At a given altitude and a given mach number, the indicated airspeed will be the same, no matter what the outside air temperature. I remember on the 727, at FL 350, mach .80 equals 272 knots. Always. At different altitudes, the indicated airspeed will be different. At different mach numbers, indicated airspeed will be different. When the temperature changes, and you stay at the same mach number, your true airspeed changes, but not your indicated. Good luck understanding all of that.
I understand believe it or not... Mainly concerned with IAS in this case, because of the overspeed situation mentioned above... So I guess I have to constantly 'reset' (set to .80, and back to .81 again) when I'm in a climb or descent since it doesn't seem to 'update' the bug on the speed tape.
Heres another question - you said it depends on altitude. Well FL350 is not always equal to true altitude... Or does it cancel this out because of the pressure involved is the same?
When do you switch to IAS to Mach? I heard that the magic number is FL260, but what determines this? (I know that for compressibility reasons you make the switch when at high altitude, but how do you know when?)