Re: Power Hungry air conditioning ?

From: (Sense)
Organization: America Online, Inc. (1-800-827-6364)
Date:         17 Mar 95 12:58:01 
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The APU is used to power the AC is correct, but it also powers all of the
plane's electrical systems, and I think the hydraulic as well.  When the
engines are running, the APU is turned off and engines power the entire
plane.  In order to keep maximum power to the engines, the APU can be used
as a "battery" to run the other systems of the plane (since the AC, like
in your car, eats plenty of juice), and relieve some power from the
engines from having to run 10 or 15 percent of the electrical motors and
part of the AC.  Some airlines run the APU a couple of miles pre-arrival. 
This also acts like a battery and gives a little of boost in handeling
performance.  On a 767, it also stresses the APU Air Inlet Door Actuator
which my company manufactures.