Re: Re[2]: Fed Ex MD-11 crash was mechanical

Date:         28 Aug 97 02:30:44 
From:         "nite rider" <guesswho@memphisonline.com>
Organization: Big and Purple
References:   1 2
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Joel S Cole <stevec00@juno.com> wrote in article
<airliners.1997.1838@ohare.Chicago.COM>...
> Nite Rider,
>
> 	I would like to respond to your email stating the MD11
> experienced a wheel failure and ask a couple of questions.
>
>   [1] Who are you?  What is your source?

Just think of me as a sort of Matt Drudge-like source who wishes to remain
anonymous. I'm not a journalist, and this is the internet, and I did say my
source was heard from within the company (i.e., second/thirdhand) so don't
hold me to anything resembling a major network evening news broadcast
journalistic standard, please.

Hint-- no bonus for me.

>    	Several rumors have surfaced about this incident, and most,
> like your email, has the wrong facts.  The data quoted in your email does
> NOT agree with that in the latest Aviation Week.

The only glaring error I saw (yes I saw the AW article at
http://www.awgnet.com/safety/nzfedx11.htm) was the 1.2g figure versus the
1.7g figure in the AW article. Actually, the first figure I heard was
"about 1.6g" but 1.2g seemed to come from a more reliable purple source. I
stand by my claim that the focus of the investigation shifted to mechanical
failure, though I am no longer inclined to draw conclusions from this. At
any rate, the depth of the information I received is indicated by the fact
that I didn't know the aircraft had bounced and experienced a second
impact. After hearing that, I decided this accident is more complex than we
thought. Now I have more questions that remain unanswered.

>   [2] When you say the crash was due to a failure of the "wheel
> assembly", do you mean Wheel Assy or Tire Assy?

Neither because they didn't say, though the condition of some of the pieces
indicated mechanical failure. That's why the focus of the investigation
shifted to mechanical failure, apparently. Besides, the crew interviews
were completed. Note the right main gear continued down the runway? This
seems to suggest it separated early in the chain of events.

> 	After inspecting the failed landing gear parts, I tend to believe
> your version; especially when #4 Tire had above average landing cycles on
> its carcass. However it must be pointed out that FedEx never experienced
> a Wheel failure on a DC10 or MD11.  We've had Tire and also Bearing
> failures with little, if any, secondary effect.  I recall the DC10 that
> lost the entire Nose wheel on takeoff from England and landed in MEM with
> no damage.

I still have many more questions than answers (or rumors). How much roll
and yaw did the aircraft experience at the time of the second touchdown?
Was it aggravated by crew input? Was this an autolanding (If so did the
throttles remain symmetrical throughout?) Which part of the aircraft
impacted first after bouncing? Did the anti-skid system function normally?
Did the gear fail on the first or second impact?

>   [3] Even if there was a "Wheel failure", why would this result in a
> Gear collapse at an approach of 460 fpm and 1.2 g's?

I never said "wheel failure", I said "wheel assembly", which is less
specific. There are many possible factors involved-- how about strut
underservicing, brake release failure (anti-skid malfunction), tire
separation during wheel spin-up, metal fatigue (lots of cycles on this
aircraft and previous history of hard landings), to name a few? If the
right-hand undercarriage were to collapse it would in turn cause the
aircraft to roll right, with the #3 engine impacting the runway, and
possibly wing-tip impact; this in turn would aggravate the yaw condition,
resulting in a snowballing effect and total loss of control.

> 	Either your numbers on the approach is incorrect (again, refer to
> AV Week) or you have underestimated the strength of the landing gear
> design.

Not considering the yaw and roll at the point of second runway impact. The
sideload stresses involved were probably more than a match for a weakened
gear structure (this aircraft had a hard landing history) and possibly
excessive even for a perfectly intact gear structure.

> My guess is maybe a tire blew on the first touch down and there
> was no gear failure.  (Think of it; why would the aircraft bounce if the
> gear broke?)  The troubles occurred at the second touch-down: higher g,
> right roll.  But then the right wing drop could only be attributed to
> pilot input. Coming down on only ONE strut, the one that has a flat
> tire, maybe could cause the strut to fail.

Only pilot input? Wouldn't gear collapse on first rebound cause a yaw and
roll to the right? How about asymmetric autothrottle response-induced yaw?
Wheel lockup on right main at touchdown? Asymmetric strut servicing?
Tire/hub assembly separation on wheel spinup? Loss of hydraulic downlock
pressure? I do agree that the most likely cause of catastrophic wheel
assembly collapse is a hard touchdown on an excessively loaded gear, due to
roll and yaw.

Again, more questions than answers.

Incidentally, the first officer was credited with going back into the
aircraft and pulling out the two jumpseaters inside who were still dazed,
hanging upside-down from their straps.

nite rider