Re: ETOPS Question

Date:         25 Sep 97 01:39:45 
From:         faurecm@halcyon.com (C. Marin Faure)
Organization: Northwest Nexus Inc.
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In article <airliners.1997.2181@ohare.Chicago.COM>,
"[non-spam]jfmezei"@videotron.ca wrote:

> C. Marin Faure wrote:
> > limit.  After several bad crashes of twin-engine piston airliners in the
> > 1950s after they lost one engine and burned up the other one trying to
> > reach an airport,
>
> On modern jetliners, if one engine fails during cruise, is the remaining
> engine really used to the max ?

No.  The problem stemmed from piston airliners that did have to run at
very high power setting to continue flight.  Unlike a turbofan engine, the
chance of failure in a piston engine increases steeply with power.  As
long as you don't overtemp it, a turbine could care less what power
setting you run it at or for how long.

> Or is there still a need to limit single-engine operations to a certain
> length because the remaining engine, being tested to its limit, really
> has a higher risk of failure ?
>
> > safe flight after the in-flight shutdown of an engine.  The fire
> > supression system must be able to keep a lower hold cargo fire from
> > spreading for 180 minutes, the backup electrical and hydraulic systems
> > must be able to keep the airplane's control systems functioning for 180
> > minutes, the battery(s) must be able to keep certain critical
> > communication and navigation systems functioning for 180 minutes, and so
> > forth.
>
> Are these requirements any different from 3 or 4 engined jets ?

No.

> Considering the
> history of fires which consume airplanes in the matter of minutes, if
> you can survive 180 minutes after a fire has been declared, doesn't this
> mean that the fire was totally extinguished and hence, you could
> continue forever ?

No.  Fires can smolder for a long time.  Sometimes the only thing keeping
one from bursting into a full-fledged conflagration after awhile is the
fire supression system.

> Also, for the backup electrical/hydraulic systems, if one engine fails,
> won't all these systems continue to operate safely from the remaining
> engine?

You'd hope so, wouldn't you.  But what if the generator fails on the
remaining engine, or the hydraulic pump.  The engine's keeping you up, but
you've got no electricity from it or the dead engine.  You need something
else to keep your power on for the 180 minutes.

> Now, if the remaining engine fails, is it not rather pointless to
> require the true backup electrical systems (battery and prop-turbine) to
> operate for 180 minutes ?

Yes, but you want your critical systems to continue operating so you can
control the plane on the way down (like Air Canada's Gimli Glider).

C. Marin Faure
  author, Flying A Floatplane