Re: FYI, B757 crash at Bermuda.

From:         "John N. Cothran" <neilcothran@worldnet.att.net>
Organization: AT&T WorldNet Services
Date:         14 Jul 96 22:43:22 
References:   1 2 3 4
Followups:    1
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Rudi Vavra wrote:
>
> Brian A. Reynolds wrote:
>
> > 9)    A stall is caused by disrution of airflow over the wings.  If
> >  the aircraft's nose is excessively high, the airflow will be
> >  disrupted.  The angle of attack (the angle of the aircraft
> >  centerline relative to actual direction of travel) is deteced by
> >  an Angle-of-Attack sensor (AOA for short) which is a vane like
> >  device which 'flies' in the airstream.  If airspeed is sufficient,
> >  then the AOA will stay within limits.  If the angle of attack
> >  vs airspeed is insufficient, then the AOA (as measured by the
> >  sensor) will be come excessive and generate a stall warning.
>
> WRONG! The AOA is the angle between the chord of the wing and
> the relative airflow. The AOA can be exceeded at ANY airspeed and the
> airplane will STALL at ANY airspeed once a critical AOA has been
> exceeded. This is important. You CAN stall an airplane at any
> airspeed.
>
> > 12)   The flight crew experienced simultaneous stall and overspeed
> >  indications.  In reacting to the overspeed warning, the nose
> >  was pitched up to decrease the airspeed.  This increased the
> >  angle of attack, deepening the stall.
> > 13)   At some point the aircraft ceased to have sufficient airflow
> > over
> >  the wings and stopped flying.
>
> The aircraft stopped flying AS SOON AS it stalled. It doesn't matter
> how deep the stall is, after you stall a wing, lift drops
> dramatically. The plane was probably kept in a stall
> unintentionally, as the overspeed warning was still sounding. Usually
> if you stall an airplane and hold it in a stall, it will drop one
> wing quite suddenly and dramatically. In all probability, the
> airliner went inverted, or close to it after it stalled.Obviously
> there was not enough time and not enough altitude to recover from
> this unusual attitude in this case.
>
> All the above is pure speculation based on my aeronautical knowledge.
> I'll wait for the official findings in this case.
>

You are indeed correct, but I think the point of the earlier message was
that the flight crew was receiving two distinct and very different set of
inputs.  The erroneous airspeed indication could indeed have been due dut
condensation in the pitot-static system, although I would wonder why one
system did and one didnt....if indeed the probes were left uncovered, my
guess would be the proverbial "bug in the tube" problem.

As an engineer in the flight simulation industry with over 15 years
designing the math models used for flight training simulators for several
aircraft, including both the B757 and B767, I concur that the aircraft's
response in a stall would most likely be as you mentioned.  The major
problem in this incident seems to me to be the inability of the pilots to
make the correct choice based on the information available to them at the
time, and, let's face it, we may never know exactly what that was.  As a
pilot myself, I think this incident serves best as a reminder of what can
happen when we as pilots forget to observe EVERY piece of data available
to us, not the least of which is the "seat of the pants" data we get
simply by having our asses strapped to the hardware.  Let us not forget
that even the best of modern avionics and flight management systems
available to us today are not and never will be a substitute for plain
old smarts.

--
"A committee is the only
 known life form that possesses
 multiple stomachs and no brain"      Lazarus Long