Original posted by Rob21 Maybe this can explain why on "nice" runways (POA) is SOP (TAM) both TLs to reverse and also (maybe) there is another "SOP" selecting only one TL to reverse on the "good" engine when runway is slippery (CGH).
Rob21, if you are correct, on the landing of the previous track (CGH-CNF) the procedure should have been both TLs to reverse, because of the Confins runway's lenght.
At the present, two are the hypotesis: a interface/software defect or a human error. I suggest to discard the idea of the physical locking of the TL, because, with much probability, the reaction of the crew should have been different, since in this case they should be aware of the problem with the engine. In all this thread I didn't find any mention of the occurrence of events of the first type, so I think that this hypotesis is very improbable, even if not impossible. For the human error, since it is not the first time that it caused an accident (and we can ask ourselves how much times similar faults occurred without consequences), the probability is higher.
Original posted by PBL AI's position on (5) will be that, until the Congonhas accident, there was little evidence that failing to reduce thrust to idle on flare was an oft-repeated error. There were two incidents on record in (what AI claimed in its deposition) over 30 million fleet landings in 19 years.
I disagree. In general, between the various causes of many accidents, we can find events whose occurrence is very rare, and the task of safety's professionals is to prevent them. If the Taiwan's accident had occurred on a shorter runway, it could be more tragic. Moreover, from a purely statistical point of view, the accident of Congonhas didn't transform this kind of mistake from rare to oft-frequent. We could speculate that, if, after Taiwan, AI had made mandatory everywhere the procedure with both TLs to reverse, maybe the accident of Congonhas couldn't occurr.
I think that, with some probability, the mistake did originate from a discrepancy in the interfacing between machine and man, because the former operates only on the basis of the binary logic (1-0, yes-no), while the latter is
educated to operate in this way, and often resume some logical processes under "frames" (in German: Gestalt). One of these could maybe be "one TL forward and one backward". It is only a hypotesis; I think that the important thing is that the professionals of the field can learn something from these tragic events, i.o. to improve the safety of aviation.