Re: 777 landing gear

From: (James T. Ringland)
Organization: Sandia National Laboratories
Date:         01 Jul 95 02:24:40 
References:   1
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In article <airliners.1995.881@ohare.Chicago.COM>,
   Joe Diederichs <> wrote:
>Recently somewhere (maybe in this group) I read what I will for now
>consider a rumor about a key part of the 777 landing gear being
>under-designed by exactly a factor of 1/2.  Supposedly this results in
>the replacement of this item being an annual maintainance task.  The
>point was that, while the CAD systems allow fast design and accurate
>details, fast design cycles allow less time for cross-checking the big
>picture.  Being an electronics designer myself, one of my biggest
>concerns when doing a design is not missing some crucial overall aspect
>while getting all the little details right.
>Can anyone substantiate this?  If so, what part or parts are involved?

This was written up in comp.risks two months ago and I found it interesting
enough to save.  That post is copied below.  This may be what you saw.  I know
no more than what is written here, so I too would appreciate more information.

Jim Ringland

Date: Tue, 4 Apr 1995 23:38:16 -0700 From: (Nathan Myers)
Subject: Boeing 777 has dainty feet

I have heard recently that the new Boeing 777 jetliner, described in recent
news reports as "skating through the approval process", has a little problem
that might be interesting to RISKS readers.

It seems that an important part of the landing gear is too weak, and will get
"used up" (through metal fatigue), and need to be replaced annually. While
this is probably not a safety problem, it's an extra expense (frequent
inspections and replacements) and an embarrassment.

Unfortunately, fixing it isn't just a matter of making the part stronger; it
would then be bigger and heavier, affecting fit, balance, and nearby parts.
This sort of problem is familiar in the "shakeout period" of all previous
jetliners, but it's surprising that it showed up so late in the approval
process.  (A previous 7?7 has a nonlinearity in the landing gear linkage that
caused an oscillation when trying to close the doors; it was fixed by an
appalling hydraulic "patch" that cancels feedback during the nonlinear portion
of the cycle.)

How did this mistake get all the way through Boeing's legendary engineering
process?  The 777 is the first commercial Boeing to have been modeled entirely
on computer before construction.  Apparently the part is precisely a factor of
two weaker than it should have been.  Does this smell like a structural model
entry error?  I have been unable to find out more about the source of the
error, and would welcome more detailed information.

Maybe the RISK is in streamlining your engineering process so well, and
eliminating so many of the more common mistakes that would have caused delays,
that you are already getting final FAA approval before the booboos that only
time can reveal are noticed.  Or maybe the RISK is just that better
communications can leak word of embarrassments few would have known about