I have just returned from Papua New Guinea and I’ve had a week of watching Air Crash Investigation on Nat Geo. I think I saw 6 episodes and enjoyed them all from a personal and professional perspective.
I had seen some episodes before but most were new to me. Almost all of the episodes examined a crash or series of crashes which were caused by an intentional breakdown of procedure caused by a breakdown in self discipline.
In one episode, a Boeing 757 eventually stalled and spun to the ground because of an airspeed disagreement between the Captains and Co-pilots airspeed indicator (ASI). The Captain had also engaged the auto-pilot which took its airspeed input from the Captain’s ASI which was apparently over-indicating significantly due to a blocked pitot tube. To cut a long story short, the over-speed warning sounded and there was confusion as to whose instrument was accurate. In an effort to reduce the (apparent) speed and silence the over-speed warning the Captain reduced thrust which, because of the low (real) airspeed, caused the aircraft to stall and crash.
Sadly the accident could have been prevented if the Captain had followed a simple but basic procedure on take off. During the take off run, the co-pilot called 80 knots and at this point the crew must confirm that both ASI are in agreement. If they are not as was the case with the 757, the Captain should abort according to the airline’s procedures. At this speed, this should not cause significant problems in most cases. In spite of this, unfortunately, the Captain noticed the discagreement but elected to continue with devastating consequences a few minutes later.
This episode caused me to wonder why it is we sometimes ignore or somehow amend tried and proven procedures. I suspect we all unconsciously undertake a simple risk analysis which due to the circumstances occurs in a fraction of a second, and due to a number of factors we get it wrong! Let’s be honest, in life we have all done it even if not in the aviation context.
The unconscious risk analysis however will sometimes be flawed because it cannot include all relevant information, the environment changes and or, often we have a situational inbuilt human bias which can rationalize any risk. A classic example of this is human bias is something like, “Get-home-itus” which partially compensates the real potential or consequence of the activity in our mind. So all aviation participants whatever role we play must guard against snap decisions which are contrary to procedures. We must be very disciplined to resist our biases and follow tried and proven procedures. Only on very rare and dire circumstances using all crew and other resources available to us, should be consider otherwise.
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