Re: A brief commentary

From:         "Rudi Vavra" <flying@ozemail.com.au>
Organization: Goodfox Pty. Ltd.
Date:         14 Jul 96 22:43:24 
References:   1 2 3 4 5
Followups:    1 2 3
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> This is the second time in recent weeks that I've read of a fatal
> accident caused by a preventable stall, the other incident being the
> BirgenAir B757 crash, where the instruments supposedly said "Speed
> up!!" and "Slow down!!" at the same time, and the pilot made the
> wrong choice (at least, that is the speculation prior to the NTSB
> report).  Why did the pilot in the accident mentioned above slow
> down to V2?  It sounds like some kind of SOP which could have been
> dispensed with.

The pilot slowed down to V2 BECAUSE he was trained to do so in that
scenario. With the loss of one engine (remember, the crew did not
know that they lost the whole engine including the pylon, the
assumption was that the engine lost power), the SOP was to slow down
to V2. This airspeed probably corresponds closely with the "best angle
of climb" airspeed, and this procedure was implemented so that all
ground obstacles are cleared safely before the crew "clean up" the
airplane and decide on further action. In an emergency, you have to
fly the airplane first. This is what the crew were doing. With the
benefit of hindsight, higher airspeed should have been maintained,
and control of the aircraft would not have been lost. Emergency
procedures were changed accordingly. When it happened, though, the
crew were doing everything as they were trained, and although it was
the wrong thing to do in this case, in the majority of aviation
incidents and accidents, the crew emergency training is the only
thing that saves the lives of the passengers. If the same incident
happened today, it'd most probably be just that, an incident,
because the crew would react exactly as they were trained (SOP was
revised after the accident).

> The BirgenAir decision seems even more dubious.  Unless I'm much
> mistaken, a B757 is not so overpowered that the engines can push it
> past the max airframe speed in level flight.  This one was climbing
> and relatively full, which suggests that an overspeed airframe
> failure was all but impossible.  I'd be interested to hear
> otherwise.]

Aaah, yes, but again, you are analysing this with the benefit of
hindsight. Spatial disorientation is a very powerful and deceiving
sensation. The only way to combat it is to trust your instruments.
When your instruments don't agree, it's very hard to decide which
instruments to trust.

We are all human, and one of the human traits is to stick with your
convictions. Once the crew make a decision and elect to trust one set
of instruments, they will go with that decision even if all
subsequent events try to tell them that their decision was wrong. It
takes a clear analytical mind to evaluate these signs and break the
chain. There are plenty of examples of this "fixation", the flight
that went into the ground because the flight crew were trying to
figure out whether the front gear was down and locked, or whether the
green indication light was faulty. Even though the ground proximity
warning sounded some twelve seconds (from memory, don't quote me on
that) before impact, no one pulled back on the yoke, because the
whole crew was convinced they were flying at 2000 feet. They
convinced themselves that the GPW was faulty!!! (The power of
assumption.)

Rudi


--
Rudi Vavra <flying@ozemail.com.au>
http://www.ozemail.com.au/~flying
(Those Magnificent Men and Their Flying Machines)
--
<<The beatings will continue until morale improves.>>