Greg Deen started a thread about Error Chains about a week ago. Greg and I are
partners, though we are 500 miles apart (geographically, not philosophically).
I usually refrain from commenting on his inputs here since we usually see
things alike. But Gregâs question, ãHow do you know you are in an error
chain?ä, piqued my fancy enough that I started a response. Then, as usual,
Doug Edwards beat me to the punch with his comment: ã. . . how to
differentiate a normal step in a sequence from one sufficiently abnormal to,
uncorrected, (that may) lead to the incident/accident."
As I began to modify my response to Greg, to give credit to Doug for his
thoughts that paralleled mine, Sakumasan came on line with the ãrain dropä
example. And, though I hate to admit it, is much more eloquent that my
decision tree example full of yes, no, and Îif thenâ choices and directions.
Sakumasanâs example provides the randomness that I was struggling to
incorporate.
Then Graham Braithwaite came along and pointed out that ãas human componentsä
in a system, ãwe are all in countless interwoven accident chains and so we
must not fixate on avoiding single ones."
The final blow to my response to Greg came from yet another quarter, Vince
Mancuso. With cool logic he quoted himself with a brilliant piece of self-
evident truth . . . ãWe cannot respond to something that we do not
recognize....ä
So here I sit with most of my own brilliant, incisive thoughts co-opted by my
colleagues, when it occurs to me could we all be right.
An error chain in retrospect seems easy to define. Reasonâs model can be used
to demonstrate when the ãholesä line up to lead to an accident. But if we move
one of the templates just a little, another possibility (or possibilities)
appears. That is the situation faced by the crew in flight. Like Sakumasanâs
raindrops on a pane of glass, the possibilities are endless. So what then
would be the prospect of identifying which of those possibilities are going to
lead to disaster.
Surely then we can train crews to recognize a pending problem. Our teaching
focuses on the decision process and situational awareness. As a decision is
reached, the other possible choices should be examined for their potential for
incident/accident/danger. If one of them could lead to trouble, one should
progress (mentally) back up the decision tree to see if there was an earlier
fault and what were the consequences. Great philosphy, given the time for
musing and analysis. But this process suffers in practicality if the process
is occurring on short ILS final in bad weather, with airplane problems.
So now we are back to the Mancuso/Edwards approach of train to
recognize/respond to error producing conditions. I wait with bated breath for
Vinceâs list of error producing conditions. Doug has created a training
program to psychologically prepare the pilot to respond to certain stimuli.
Maybe with Vinceâs list we can move further in that realm and truly develop a
recognize/respond system. But remember Sakumasanâs raindrops and Grahameâs
warning. There is an infinite number of combinations that can cause trouble,
and I suspect that many times the salvation from the ãerror producing
conditionä will be instinctive rather than cognitive.
We refer to Dougâs ãhabit pattern interventionä with a device called an
assertive statement. The Air Mobility Command of the USAF has formalized this
concept in a manner not unlike Dougâs ÎRed Flag!â. The term used is ÎTime
Outâ. It may be used by any crew member when he/she wishes to ãprovide a clear
warning sign of deviation or loss of situation awarenessä. It does provide an
opportunity to break the error chain prior to a mishap. The term, since it is
a regulatory part of their culture, alerts all crew members that there is a
problem. The pilotâs required reaction is: SAFETY PERMITTING, stabilize the
aircraft and resolve the problem. Included in the procedure is the comment
that: ãThe aircraft commander retains the final decision authority." That
reemphasizes that the aircraft in flight is not a democracy, but a benevolent
dictatorship.
Well, like Grahame, I fear I have gone on a bit, but I hope light has been
shed. Thanks a lot guys for the co-opts, I am now convinced that great minds
do think alike. No brag, just fact.
Dave Wilson
Raytheon