Re: in-flight engine shutdown / antiquated ATC equip

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         17 May 95 17:25:53 
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>Whatever became of the ETOPS requirement that an aircraft had to have
>an APU (or 2) that was operable throughout the entire single-engine
>flight envelope? The idea was that the air conditioning and other
>non-essential loads would be shifted to the APU ...

I don't see where ETOPS would concern itself with non-essential
loads.  That's not to say AC is non-essential, if the loss of it
requires a lower altitude which in turn increases time to reach
an alternate landing site.

In any case, there is no requirement that an APU must be operable
throughout the full envelope, just that power for electrical and
hydraulic systems has more redundancy than just the two engines.
Airbus did choose to meet this requirement on the A300 and A310
via an APU that can operate throughout the envelope, with the hard
part being starting the APU at altitude after an extended cold-soak.
Boeing does not do this on the 767 (or 757), instead opting for a
RAT (ram-air turbine).  While fortuitous for the Gimli Glider, this
adds equipment (thus weight and added maintenance) vs the Airbus
APU solution.  Nevertheless, Airbus uses a RAT on the A330 and also
the A340.  (Obviously not for ETOPS on the A340!)

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