Re: 747

Date:         10 Jul 97 17:46:12 
From:         "matt weber" <mweber@cyberltd.com.au>
Organization: Customer of Access One Pty Ltd, Melbourne, Australia
References:   1
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V. Venkatesh <vangal@u.washington.edu> wrote in article
<airliners.1997.1366@ohare.Chicago.COM>...
> A cousin of mine was flying Sea-Tokyo on a NW 747 on Monday when the
> captain shut down two engines near Alaska and returned to Seattle. I guess
> this isn't much of a deal since nothing appeared in the news. When a 747
> is flying along on 2 engines, what happens to speed, altitude and total
> fuel consumption? I am guessing speed, altitude decrease and also possibly
> total fuel consumption since only 2 engines are running.

Depends very much on weight,  and which engines but from your description,
the aircraft was probably pretty heavy, so the max altitude will fall, as
will the speed. The reduced speed will require different (dirtier) trim
settings, and this may result in increased fuel consumption, but probably
not by much. P3 Orion are often cruised on 3 engines to improve time on
station. Fewer engines running generally means better fuel consumption all
other things being equal.

If you lose both engines on one side, that will require a good deal of care
not to get too close to minimum control speed, and will require a large
trim input, which means lots of drag, and probably substantially increased
fuel consumption.

If it is one engine on each side, and is symmetric (both inboards or both
outboards) trim adjustment is likely to be quite modest and fuel economy
might actually improve.