PBL,
thanks for your clarifying iportant aspects about statistics and statistical (in)significance.
Another point may always be if you can show a
causal link between the locked reverser and the crew mishandling the thrust levers in the flare. (I stress again: the mistake was made while pulling levers to idle in the flare, reminded to by the "Retard!"-calls, and
not while selecting reverse).
To show causality you need a number of necessary causal factors, and you need to show that these are sufficient.
A well-known way to check for necessary causality is application of the counterfactual test, one of its informal representations may be:
"B is a necessary causal factor of A, if, had B not happened, A would not have happened, either."
Thus, to show that the locked reverser was a causal factor of the flight crew not pulling thrust lever #2 to idle, the following must be true:
Had the thrust reverser not been deactivated, the crew would have pulled the thrust lever #2 to idle.
How can we tell if that is true?
We can try to speculate phycologically that the knowledge about the locked-out reverser, and the reminder shortly before landing about "remember, only one reverser" may have influenced the crew's actions, but this still will not satisfy the counterfactual test, although perhaps some probabilities may be arrived at by human psychology experts.
Secondly, even if we take it as true, we are certain that it is not sufficient. There were hundreds of thousands of landings with locked reversers and proper handling of the thrust levers. So we need at least one other necessary causal factor to explain why the crew made this particular mistake in this particular instance. One can imagine high work load, inexperience on type, CRM issues, training, ... as necessary causal factors, but it seems doubtful that we can ever show causal sufficiency.
I am sure the investigators will look at all these in detail and work with experts in the field and may find it necessary to further stress the importance of adhering to SOPs and of discipline on the flight deck, as matters of training.
If and when the official investigation points to such causes, which will have to pass the "IN/
JS" criterion (Individually Necessary / Jointly Sufficient), I may augment my Why-Because Graph with nodes showing the factors leading up to the crew mistake.
Bernd