Re: Photo of Pan Am 747 W/5 engines

From:         Tony Maddern <tmaddern@cse.unsw.edu.au>
Organization: University of New South Wales
Date:         03 Nov 96 19:57:00 
References:   1 2 3 4
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McElravy asked:
>
> How is the extra engine mounted? How long does it take to mount/unmount?
> How much extra does it cost to haul a spare around? Are airlines allowed to
> do during normal commercial flights? If so, how often does it really
> happen?

Spare engine carriage (SEP) ability is an option that is ordered before
the aircraft is built. A hard point is built into the wing, usually
inboard of the left hand engine(s), onto which a mini-pylon which
carries the engine can be attached. The engine is pre-prepared for
carriage and then simply bolted to the mini-pylon and a stream-lined
fairing placed around it. Our engineers could demount the new engine and
mount the broken engine ( for return to the shop ) in one hour.
There are quite severe performance penalties with SEP so it is only done
when alternative freight methods are not available.
SEP is conducted on normal revenue flights as it is a fully certified
operation. With more and more wide-body freighters in operation and the
increased reliability of jet engines it is now an unusual occurrence.

Tony Maddern (ex-Cathay)