Re: ETOPS Question

Date:         01 Dec 97 02:33:57 
From:         wieni@aol.com (WIENI)
Organization: AOL Bertelsmann Online GmbH & Co. KG http://www.germany.aol.com
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For all ETOPS flights the APU is a NO-GO- item. Therefore it's of course
certified for operation and starting in cruising altitude. For this reason all
APU's I know have an oil heater, which is permanently on to reduce the drag
when starting in high altitude.
A very important fact for APU starting capability in high altitude is the
pressure ratio of intake vs. exhaust. This is a major driver when choosing the
APU intake position.
The APU bleed is not only necessary for engine restart but also for cabin
ventilation and pressurization ( perhaps more important).
In case of no electrical power from the main engines there is also a ram air
turbine on AIRBUS A/C delivering power for the basic systems.

[Moderator's note: Boeing's twins also have a ram air turbine.  -- Karl]

Best Regards Mat