Re: hydraulic problems with DC-10's??

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works
Date:         Wed, 18 Nov 1992 20:50:05 GMT
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In article <airliners.1992.6@ohare.Chicago.COM> sdl@linus.mitre.org writes:
>Some of my pilot friends have accused the DC-10 as having a
>particularly bad history of hydraulic problems (which have
>contributed to a few crashes).

Two, at least.  AA 191 at Chicago/O'Hare on May 25, 1979, and UA 232
at Sioux City, Iowa on July 19, 1989.  The Turkish Airlines crash near
Paris on March 3, 1974 helped set up UA 232 though I'm never seen any
reference to the hydraulics as being contributory to that crash.

>But do the statistics really support the notion that the DC-10 really
>has a significantly worse safety record than other wide-body jets, or
>is this just a myth?

After the A320 crash at Strasbourg early this year I saw something
that said the A320 had overtaken the DC-10 as having the worst safety
record of any large jetliner and that both were an order of magnitude
worse than the third-place contender.  I really wish I could find the
reference, but alas, I can't.  I don't recall the metrics used, and
one could certainly debate the statistical validity given the small
samples involved.

Another view is to look at the number of airworthiness directives (AD)
issued by the FAA in the US for the DC-10 versus its contemporaries.
As of January 1, 1982, the DC-10 had 148, far ahead of Boeing's 747
with 57 and Lockheed's L-1011 with 51.  The FAA clearly found a lot
more to worry about in the DC-10.

Probably the best general interest discussion of the DC-10 and all its
problems is in The Sporty Game, by John Newhouse (Alfred A. Knopf, New
York, 1982).  Chapter 5 in particular goes into great detail, though
it of course predates the Sioux City crash.

>Also, have all these hydraulic problems been corrected, or does the
>DC-10 still suffer from hydraulic problems even today?

The DC-10 (and the MD-11) haven't "suffered" from them recently,
though the problems still exist.  Fundamentally, the DC-10's hydraulic
system shortcomings as compared to the 747 and L-1011 are that there
are only three, instead of four, giving less redundancy, and they tend
to be routed together so that something which affect one probably will
affect all three.  Boeing and Lockheed (and I believe Airbus) used
three hydraulic systems in any one area of the plane, providing the
mandated redundancy, but used four overall so that a problem which
caused the failure of all three systems in one part of the aircraft
would still leave control in other areas via the intact fourth system.
They also chose to route the three systems independently, again to
minimize the possibility of complete failure.

As mentioned, I don't believe the Paris crash involved the hydraulics,
but it did lead McDonnell-Douglas to relocate the control cables and
hydraulics from under the cabin floor, where the cables had been
severed by a collapsing floor, to the top of the cabin.  This simply
left them vulnerable to a different failure mode -- demonstrated 15
years later when the fan on UA 232's #2 engine disintigrated and sent
shrapnel through the top of the aft fuselage, including all three of
those hydraulic lines.  Clearly a more reasonable solution would have
been to move only *some* of the lines after the Paris crash, but this
was not done and has not been done since, though some check valves
were added to minimize the impact.

The vulnerable location of the hydraulics at the leading edge of the
wing, instead of a mid-wing and/or trailing edge location as used by
other manufacturers, precipitated the Chicago crash, and the lack of
any mechanical locking mechanism to prevent uncommanded flap retrac-
tion also played a significant part.  (The largest blame was placed
on American Airlines for improper maintenance practices, though the
airframe certainly received its share of blame.)  While I believe the
locking mechanism was later added, nothing was done about the routing
of the hydraulics.  Indeed, American requested a modification kit to
move the hydraulics and was willing to pay for it, but McDonnell-
Douglas refused.

I'll leave you to draw your own conclusions, but I certainly do not
feel comfortable flying on the DC-10, even though I've flown on them
many times.  I fly SFO-ORD somewhat often and do my best to catch one
of the 747 flights United offers or a 757.

-- 
Karl Swartz	|INet	kls@ditka.chicago.com		
1-415/854-3409	|UUCP	uunet!decwrl!ditka!kls
		|Snail	2144 Sand Hill Rd., Menlo Park CA 94025, USA
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