spfoster
I never knew you couldn't prime ALT ACQ from MAX CLIMB / MAX CRUISE. I was thinking though that if you had ALT HOLD selected then the autopilot wouldn't be able to vary the pitch attitude and it would hold at the ALT HOLD level. Once there it wouldn't be able to use pitch to increase or decrease speed if necessary. I can see how the autothrottles could hold the speed back but if it were to get warmer then even at full power it may not be able to maintain speed at a fixed altitude.
I'm sure there is a simple answer which will leave us saying "oh yeah, how obvious, didn't think of that"
Just strange it doesn't seem to be written anywhere.
Hi again Steve. At FL600 your aircraft is going to be relatively light, and your autopilot is set to ALT HOLD mode. As the aircraft continues to burn fuel it will 'try' and climb, but the ALT HOLD mode will of course slightly reduce pitch attitude to keep prevent the aircraft from climbing. The autothrottle in MACH HOLD mode can keep us from straying from Mach 2, large positive temperature shears were to my knowledge almost unheard of, and so any speed reduction was exceedingly unlikely. We really need a pilot's input here to further clarify the realities of LHR-BGI supersonic cruise; that's the way the AFCS was designed to do things however.
Dude
