Re: ETOPS

From:         faurecm@halcyon.com (C. Marin Faure)
Organization: Northwest Nexus Inc.
Date:         05 Nov 96 04:13:57 
References:   1 2 3 4 5 6
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In article <airliners.1996.2226@ohare.Chicago.COM>, Steve Lacker
<slacker@arlut.utexas.edu> wrote:

> C. Marin Faure wrote:
>
> > The first jet engines were less reliable than the piston engines of the
> > same era.
>
> By "first jet engines" do you mean, for example, the J-57s of the 707?

Yes.  The very FIRST jet engines often shed parts during takeoff, several
incidents of which were related to me by Tex Johnston, the Boeing test
pilot on the B-47, B-52, and 707 programs.  But the jets used on the early
707s and DC-8s had their problems, too.  The Wright R-3350 and the Pratt &
Whitney engines (not the Wasp Major, however) were pretty reliable
considering what they were.  Their TBOs were low and they required a lot
of maintenance, but they weren't bad for piston engines.  The ealier jet
engines, however, did not perform up to expectations for a number of
years.  I've talked to B-52 crewmembers, for example, who told me that
they considered it remarkable if all eight engines were still running
after takeoff.

> > They have steadily gotten more reliable until today engine
> > failure can almost be ruled out as a potential problem, assuming proper
> > maintenance and operational procedures, of course.
>
> Again, "almost be ruled out" is a pretty strong term. I was shocked when
> I first flipped through the NTSB report page
> (http://www.ntsb.gov/Aviation/months.htm) to find a surprising number of
> "uncontained engine failures." Most of these weren't losing whole fan
> disks and killing people like the recent MD-88 or the Sioux City DC-10,
> but most represent total engine failures nonetheless. Statistically, yes
> its a small number of failures per number of flights... but in my book it
> can't "almost be ruled out" until the total probability of such a failure
> gets down to the "once in 10 years" sort of range. We aint there yet!

Again, it depends on what engines you're talking about.  The newest
high-bypass engines used on planes like the 757, 767, A-310, A-330, and
777 are incredibly reliable.  More so that the engines used on 727s,
DC-9s, and so on.  As I said in an earlier post, as of the last time I
looked at the statistics there has never been a case of both engines on a
commercial twin-engine jetliner failing for different causes.  As far as
ETOPS operations are concerned, the airlines no longer consider engine
failure the most likely potential cause of a problem.  If there is a
problem on an ETOPS plane, it is much more likely to be a systems
problem.  And since ETOPS planes use the same systems used on 3 and 4
engine planes, the potential of a problem on an ETOPS twin is no different
than the potential of a problem on a 3 or 4 engine airplane.

C. Marin Faure
   author, Flying a Floatplane