Date: 21 Nov 97 01:59:52 From: firstname.lastname@example.org References: 1 2 3 4 5 6 7 8 9 10 11 12 13 Followups: 1
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Karl Swartz wrote: > >One other point. The APU cannot be operated in the air on the > >B747-100/200 series...of running during takeoff, the APU on the B747-400 > >can be used upto approx 15-20,000 ft. > > The first part of the definitely is not true. From the NTSB report on > the February 24, 1989, UA 811 accident, which involved a 747-122: > > The auxiliary power unit (APU), which was used during the takeoff, > was shutdown shortly after making the initial power reduction to > climb thrust. ... > I'm pretty sure none of the Boeing airliners have APUs certified for > re-start once cruising altitude has been reached, primarily because > of problems getting it lit after an extended cold-soak. That doesn't > imply that it *can't* be started in the air, and perhaps at lower > altitudes it might work if you had to try it. Let's understand some about almost any aircraft. There are certain components on an aircraft, such as an APU, which are not normally certified for use in the air. However, this does not prevent a carrier from modifying the component and getting it certified for use when airborne. The main reason I made the earlier statement about the B747-100/200 is that the intake of the APU would not allow an adequate air supply in order to start an engine while airborne. In some cases APU's are certified for use in the air, but for electric only.