Originally Posted by PBL
People who think that the only cause (read "causal factor") was the pilot failing to reduce thrust to idle might do well to read the first few inches of column space of David's article, in which he discusses the runway situation at Congonhas.
Originally Posted by RWA
Have to disagree to an extent, PBL. This appears to be one accident where the 'primary cause' is pretty clear; the No. 2 TL being left in the 'CLB' detent (or, to be strictly accurate, being recorded by the FDR as being left in the 'CLB' detent, and duly interpreted as such by the systems) resulted in about 55% N1 forward thrust being delivered by the starboard engine throughout the landing run. In addition, and arguably more important, the incorrect TL position prevented ground spoilers and autobraking from being deployed.
I don't think PBL is denying that this is a causal factor in this accident. He is simply contesting the notion that it is the only cause, or even the
Primary Cause.
The notion of "Primary Cause" as such is problematic, because it is impossible to create an objective prioritisation of causal factors (see last paragraph).
To make a causal explanation of an event, one needs to ensure that the causal factors that lead to it, are (a) individually necessary, and (b) jointly sufficient.
This means that, leaving thrust lever #2 at CL detent during a landing is most likely a causal factor in this incident. (Using the counterfactual test to determine causality:
Had the thrust lever #2 not been left in the CL detent, the accident would not have occured.)
But this is not sufficient. Not all landings where this happens, end in a catastrophe. In fact there is at least one which only resulted in a no-injuries-incident. There may be others, where, except for a longer roll-out distance, nothing remarkable happened. On a long, dry runway, manual braking may well be sufficient.
So there must be other causal factors. The length of the runway comes to mind, as well as its state (presumed "slippery", although this term seems to lack a precise definition), and also the delay in the application of wheel brakes.
PBL has addressed the problem of priorisation of causal factors in his talk at the Ninth Bieleschweig Workshop:
http://www.rvs.uni-bielefeld.de/ -> Bieleschweig Workshops -> Ninth Workshop -> Negotiating Accidents. (
Direct Link).
Cf. pp 36, 54
Bernd