Re: in-flight engine shutdown / antiquated ATC equip

From:         geohull@ditell.com (George Hull)
Organization: DirecTell L.C. - Park City, UT. - 1.801.647.0214
Date:         05 May 95 03:27:16 
References:   1 2
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In article <airliners.1995.538@ohare.Chicago.COM>, petercoe@netcom.com
(Peter J. Coe) wrote:

> lchiluku@ucsd.edu (R. & L. Chilukuri) writes:
>
> >The pilot later reported that the engine had shut down. The pilot had to
> >descend to unusually low altitudes because of a loss in cabin pressure.
> >The shut-down of one engine meant the loss of an air conditioning unit,
> >and the remaining unit overheated.

I'm not sure that this description is accurate.  It is possible to
maintain normal pressurization in most  airliners . . particularly the
B-767 . . on only one airconditioning "pack".  Occasionally in normal
operations we are required to dispatch with one pack inop.  We are limited
to a lower cruise altitude, although I've had occasion to shut down a pack
at altitude and the remaining unit maintained pressurization and air
conditioning just fine.  It is possible for an airconditioning pack to
overheat, but this coincidence seems like it needs better explanation . .
and it may have happened just as you describe.

> I had heard about this shutdown, and could not work out why they had
> lost cabin pressure.  Now I know.  This is precisely the the kind
> of thing that worries me about ETOPS.  Sure it seems safe enough to
> fly an aircraft on one engine, but that one engine is now running at
> at least 200% of it's normal cruise power.  Things will be bound to
> break.  I would think that the statistics used to say ETOPS are safe,
> are flawed.  They are based on the reliability of an engine in a twin
> engine set up.  Not a single engine at greater power.

ETOPS assumptions do, in fact, take into consideration the logical
consequences of the loss of an engine enroute.  The resultant systems
losses are also accounted for in ETOPS planning.  The ETOPS twins have
extra layers of redundancy, compared to their domestic versions.  If a
twin loses an engine in an overwater situation the pilots will set a
maximum cruise power limit on their remaining engine, reconfigure systems
if necessary, and divert to an appropriate alternate airport.  A driftdown
to a lower altitude is assumed, based on that power setting.  There have
been unscheduled inflight engine shutdowns in ETOPS operations and there
have been no catastrophes as a result.  The overwater twin operations are
done with sophisticated equipment and the operation has matured and, thus
far, stood the test of time.

Another important point is that _all_ twin-engine jet operations are
conducted assuming the loss of the most critical engine at the most
critical time.  That's why the twins are all terrific performers on two
engines . . we assume that we're going to lose an engine and complete the
takeoff on one engine.  If we _don't_ lose an engine we're almost always
profoundly overpowered.  That should give you some comfort . . it feels
good to me.

> One day one of these babies is going to splash.

ETOPS = Engines Turn Or Passengers Swim . . nothings perfect, but ETOPS
operations have some pretty persuasive statistics to give us some
confidence.


George