From:         Steve Lacker <>
Organization: applied research laboratories
Date:         08 Nov 96 05:24:24 
References:   1 2 3 4 5
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Chris Dickson wrote:
> In January '89 there was a British Midland 737-400 (Flt BD-92) which crashed
> just short of the runway at East Midlands airport, England. A fan blade had
> failed on one engine. The crew shut down the wrong one and for various reasons
> did not realize it until the engine failed completely late on final.
> The AAIB reports online don't seem to go back that far - but there was
> an April 89 Flight international editorial on the potential ETOPS implications
> of this crash. This can be found at :

I went to that page, where I read the following:

  After examining systems recovered from the crashed aircraft, the AAIB is
  certain that the cockpit instruments correctly indicated severe vi- bration
  in the left engine.  Investigators note, however, that pilots distrust
  aircraft engine vibration indicators, based on experience with earlier
  electromechanical instruments.  Crews seem unaware that electronic indicators
  on later 737-300's and the 737-400 are more accurate.

  Another example of mythology triumphing over knowledge is the apparent
  perception among 737 crews that cockpit air conditioning comes solely from
  the right engine, and that smoke and burning smells in the cockpit tend to
  indicate fire in the right engine.  In fact, air supplied to the cockpit
  comes from both engines, in a 70:30 right: left mix.

This addresses some issues I have strong feelings on. If you are going to
*operate* any sizeable machine, you should have more than a casual
*understanding* of the operation of said machine. It doesn't matter if its a
bulldozer, an airliner, or your car. This also touches on the issue Karl
mentioned in another thread, that of some aircraft isolating pilots from the
actual process of flying.

First, the "isolation" issue, which is really one of "human factors" as is being
discussed in another thread. I'm not opposed to glass cockpits in planes, nor
ABS and traction control in cars- these things have their good points- however
it is essential that these systems are designed and implemented so that they do
NOT operate too "transparently."  An example can be drawn from ABS in
automobiles. In 1993, the ABS system used by Chrysler Corporation (I happen to
own one of these, which is why I picked it) creates a LOT of noise and a LOT of
brake pedal motion. There is NO doubt when you as a driver have passed the
limits of the tires and pavement and are exercising the ABS system, and I
consider this an excellent design. Unfortunately, drivers who didn't understand
the system complained very vocally and in large numbers that it was "broken" and
burned up a lot of warranty money having dealer technicians go over perfectly
good cars. The system was redesigned to be quieter and produce less pedal
movement in later cars. It is worse for this, in my opinion. Automated systems
that operate "too quietly" in the cockpit are a bad idea too. It is possible to
design an automated system that will help protect the aircraft, but still
provide plenty of warning as to the fact that it is operating.

The importance of an operator understanding the machine is apparent from the
comparison with driving a car too. Much as I would like to have a "mechanical
knowledge" section on drivers license tests, I realize this won't happen. The
days when all drivers understood the basic operation of cars went away sometime
around WWII and won't come back. Everyone drives a car, and some *will* choose
to continue to drive cars without oil, with bald tires, and with spun bearings
making sledghammer noises until they physically won't go any further.
Fortunately, the result is generally a broken car parked in the ditch- but there
aren't ditches at 30,000 feet.  The airline industry does NOT have to follow
that path, because not everyone and his dog needs to be an airline pilot. I
think it should insure that pilots obtain a good basic understanding of the
systems on each aircraft type they operate. I know that truly good pilots do
this already, and I'm not talking about a detailed understanding of physics,
aerodynamics, engine design, etc.- just understanding correctly and exactly
which engine drives what accessories, how the hydraulics are interconnected,
what various failures "feel like," etc.- the kind of knowledge that MANY people
who post to this group already have. It won't prevent all mistakes, and it might
not have changed the 737-400 incident... but if false "myths" about how a basic
aircraft system operates are indeed rampant among operators, there IS a problem.

Stephen Lacker
Applied Research Laboratories, The University of Texas at Austin
PO Box 8029, Austin TX 78713-8029