I think we are panning for gold here. I don't have anything like a
complete answer, but would like to posit some provocative thoughts.
For starters, may I change your question to, 'How do we know when a
normal sequence has metamorphosed into an error chain?'
The dynamics of flying rely on continuous forward motion. It's no
surprise that our flying thought processes follow sequences. The key
to the question thus is how to differentiate a normal step in a
sequence from one sufficiently abnormal to, uncorrected, lead to the
incident/accident. We always do the next thing (commence descent),
which always leads to the next next thing (continue descent while I
sort out this little heading problem).
I grappled with this in writng my book, in a chapter I was going to
call 'Red Flag'. It got too complicated, so I dropped it. But I did
leave in some stuff on 'habit pattern interruption', on pages 89 and
90, related to students' internalising the 'wrong' sequence, it then
becoming their 'usual' routine (habit) and how to break the chain of
causation and get them to re-learn and embed the 'right stuff'.
The 'habit pattern interrupt' technique involves a conscious decision
to suspend a routine and to take time to examine a critical issue. The
interrupt is triggered by a key word or event. The word obviously
needs to be an attention-getter. In its application to flying outside
the training arena, I saw it as operating in this way:
A step in a sequence is interpreted as being sufficiently abnormal to
call for some further consideration. A crew member says, 'Red Flag! I
believe that step calls for review.' Resort to the term mandates
response. The sequence is suspended, the next thing not done, with
appropriate advice to ATC, request for assistance, and so on. I have
some ideas on how such a procedure could have functioned in a number
of well-known accidents, but I'd like to wait and see if anyone else
picks up on - and can take further - the general idea I'm trying to
get across.
Like I said, it got too complicated for me. But, I think we may be
tracking something very important, here. Any thoughts?
Cheers
Doug