Thanks for sharing that, Jack. I've seen pictures of the failed attach
fittings. They are radiused, composite tabs which go into clevis fittings
on the fuselage in double shear. The composite fittings separated at 90 &
270 degrees (i.e. perpendicular to the shear load) leaving the sheared of
portions in the clevis'. Composites are not supposed to "see" fatigue
loads, so this is quite surprising.
I've taken some accident investigation courses from UCLA and have
participated in a number of A/C accident investigations. The photos were
not detailed enough to see the actual separation surface, but from their
general condition and delaminated state, I suspect an overload type failure,
which COULD be consistent with flutter failure.
I agree with Gary that wake turbulence would not cause a structural failure
without some underlying condition. Flutter on-set can, indeed, be sudden
and very violent. When you consider the surface area of an airliner
vertical stabilizer, you can see that even small side-to-side fluctuations
in surface pressure would mean HUGE pressure changes at the stabilizer
mounts. If the flutter stability was negative (i.e. gets worse with each
cycle) if could take very little time to become catastrophic
There is an Emergency AD from the FAA now (2001-23-51, dated 11/16/01 [just
4 days after])instituting extensive inspections of stabilizer mounts,
fasteners and control surface mounts/bellcranks on A300 & A310 A/C.
I travel a lot as part of my job, but I think I'll be asking what equipment
is being used when I make my reservations.
Dale C.
You really have to feel for New York ...
Subject: A300 crash
>>
> A friend sent this. Gary has dedicated his life to aerodynamics. He
>invented the Wheeler Vortex generator, and the "Gurney" wing on race
cars.>These are his views on>the crashed Airbus.)
>
> Howdy,
>
> Re: the New York 11-12-2001 Airbus crash.
>
> I found this photo of the vertical stabilizer's failed composite
> attachment blades, or webs. The bolts that attached the composite
vertical>stabilizer to the fuselage, remain properly attached. Clearly,
the failure>is a>delamination of the composite vertical tail, above the
points of attachment>to the fuselage.
>
> There are reasons (despite the weight savings) why Douglas Aircraft
and>Boeing have never used composites this way -- and you're looking at
one.>
> As the delamination of the composite progressed, the entire 37-ft.
tall
>vertical tail would have fluttered briefly & violently. That would
explain>why both engines were literally shaken off the airplane. (This
is
>particularly remarkable, because unlike Douglas and Boeing, Airbus
has>bragged of purposely designing their engine mounting pylons to keep
the>engines in place no matter what!) One wing tip was found several
blocks>away from the main wreckage.
>
> BTW, you'll be hearing a lot about an encounter with wake
turbulence.>
> That is a red herring. Wake turbulence can make it difficult --
maybe>even impossible to control the airplane -- but no amount of wake
turbulence>can remove the vertical tail at such low flight speeds unless
there is a>preexisting>structural fault.
>
> What is flutter? This morning, I got an email from a friend who is
the>Director of Structural Engineering of a major American aircraft
maker.
>
> He described a chilling picture: "Flutter modes often have an
> explosively quick onset, rising from nothing to catastrophic in the
> blink of>an>eye.
>
> Furthermore, the shaking can happen so fast that, despite the large
>(huge) deflections involved, an observer on the ground might not see
it. It's> just a blur.
>
> "The people in the back of the airplane would have been shaken
>senseless worse as the seats tore loose and everything was homogenized
back>there; but it was all over a few seconds later."
>
> The design weakness can and will be fixed on other Airbuses. If
not,> there are plenty of nice Boeing jetliners mothballed in the
Mojave Desert,>that can trade places with the Airbuses. In the
meantime, I'm not riding>Airbus.
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