Originally Posted by
NamibFox
I appreciate that there are efficiencies to be gained by flying higher but am informed by a corporate jet pilot of my acquaintance that there are pitfalls as well. He spoke of critical Mach numbers, higher likelihood of flameouts and the need for additional vigilance etc. How relevant is all this to the A380, 747 etc?
Polite request - Any hope of an answer to these questions. or am I on the wrong track, thread, forum?
Postscript - A bit of self investigation and I think I am beginning to answer my own questions. It seems that flight at operational ceilings might not be advisable if this case is anything to go by.
http://www.ntsb.gov/publictn/2007/AAR0701.pdf
Well, not a A380/747 specific answer (which is partly why I refrained earlier) but in general, there is no especially hazardous element of flight within the aircraft's certified envelope, provided you are also within its performance envelope (operational capability) and fly the aircraft 'by the book'.
The "max certified altitude" is the highest altitude at which the aircraft can be safely flown in complience with the various regs; it's not necessarily the altitude which is the performance limit for the aircraft - on some days that will be above the certified altitude - in which case there should be no reason not to go there, if the balance of the flight plan leads that way - on other days the performance ceiling will be below max certified, and you have no business trying to get there.
The case you list was ABOVE the operatioonal ceiling, certainly the way they got to FL410 - zoom climb/energy management is not the way to go. They ended up behind the drag curve and couldn't hold altitude and speed.
Had they 'nursed' the aircraft up there (on speed schedule etc) maybe they could have got to FL410 with enough speed to hold level flight. Still wouldnt have been a great choice, though.
That case also points to another reason not to play games near the max ceiling - you have very little in the way of excess power to get out of trouble with - at lower altitudes (provided you aren't ridiculously low!) you'll generally have lots of SEP in reserve (unless you've lost an engine of course). At or close to max alt you may already be at or close to max power, leaving no margin there. (Which is why the "standard" action to recover from stall warning - max power and just accelerate out of trouble - works pretty much ok at lower altitudes but is useless up high)