FF I'm curious about this...I read in Pilot a piece by Bob Grimstead, I think it was the 'Can a PPL land a jumbo' one in which he said that at 35,000ft the aircraft is so unstable because of the thin air that it is very difficult to keep straight and level...this may be an exaggeration but if left me with the impression that crews are slightly 'at the mercy of' the plane high up. Having said that though I believe the Quantas 707 was flown all the way from Southend to Australia without an autopilot.