From:         Malcolm Weir <>
Organization: Adaptive Information Systems -- A Hitachi Company
Date:         03 Nov 96 19:56:58 
References:   1 2 3 4 5
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Louis K. Scheffer wrote:
> I suspect the answer to this involves procedures and cockpit automation and
> human factors much more than engine reliability.  I know the limiting
> factor on most redundant computer hardware is the human element once a failure
> has occured.  Suddenly, the person in charge has to do things differently,
> using less well rehearsed procedures, and the odds of a mistake rise
> dramatically.  There are many classic cases of this; where one engine goes bad,
> and the pilot then shuts off the good engine (thinking it's the bad one), or
> where a landing gear warning light goes on, and the crew tries to fix this
> while the plane flies into the ground, and so on.
> I would suspect that a modern ETOPS plane, where the automated cockpit does
> the 'right thing' upon an engine failure (where the right thing was thought
> through by experts who were not under time pressure), is probably safer
> than a 4 engine plane where an engine failure needs to be treated with
> a long checklist and modified procedures.

I guess I'm confused.

Let's compare the A330 and the A340, or the B777 with the

Assuming similar technology engines (e.g. R-R Trents on the Boeings), is
there an argument in favor of the reliability of the twin-jet over the
quad-jet?  I certainly agree that a B777 is almost unquestionably as
good, if not better, than a 1969 vintage B747-100 in terms of
reliability.  But is that the question?

I've heard many folks in the industry claim that there is no level of
"acceptable risk", and, as a member of the travelling public, I think
this is A Good Thing!  But the whole ETOPS concept seems to stem from a
"safe enough" philosophy, as opposed to a "safest possible" one.

Now, I don't personally worry one way or the other how many engines the
flight I'm on has, but I do question some of the ETOPS-logic, as it
were, and DO believe that (at least with the PW-4084 B777) that ETOPS
ratings were granted more for Grandstanding reasons than for operational
or technical ones.

(Didn't the GE and RR B777's get 180 minute ratings from the FAA, but
only 120min levels from the JAA?).