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Old 5th Oct 2007, 22:34
  #2695 (permalink)  
gpvictor
 
Join Date: Aug 2007
Location: Switzerland
Age: 64
Posts: 10
Originally posted by PBL Some people on this thread have expressed the opinion that the only significant causal factor was the failure of the crew to reduce thrust on landing.

To show how limited such a view is, I quote from the recently-issued U.S. NTSB Summary of their report on the December 2005 overrun at Chicago Midway:

Quote:
Originally Posted by NTSB
Also, contributing to the severity of the accident was the absence of an engineering materials arresting system (EMAS), which was needed because of the limited runway safety area beyond the departure end of runway 31C.

The same obviously holds true of 35L at CGH.

PBL
I think that in the discussion about causality, some points should be stressed:

1) The causality of all events with some complexity, like plane accidents, is systemic. Even in cases like SR111 at Halifax, where apparently it seems to be possible to restrict it exclusively to the plane, it isn’t actually so, because the first factor in TSB’s report was the certification for material flammability, done far away from the plane itself. Generally speaking, it’s true that there can be a main cause (or, better, factor), but rarely it’s sufficient to explain the whole fact. In the case of CGH, we have two main factors: a) some kind of fault (human or technical), b) an airport with a relatively short runway and w/out escape areas. Every factor is necessary to explain the event, but not by itself sufficient to cause it. If the fault was done on the main runway at GRU, for example, it is probable that the crew could stop the plane. If no fault was done at CGH, this was simply a normal landing. The only difference between these two factors is that the former is a disconformity, while the latter wasn’t considered such, at least for the brazilian standards at the moment of the accident. At present, the second factor, too, is rated as faulty, since they are creating EMAS.

2) These are facts. Another fact is that TAM’s pilots operated two different procedures for landing with de-activated thrust reverser. It seems that the choice depended from the runway’s length, since the procedure first with both TL to idle and then both to rev needs 40-50 m more space than the other to stop the plane. Was the choice let to the crew, or this was some acknowledged internal TAM’s rule? At present, all pilots have to use only the first procedure. It should be expected too that AI changes the software i.o. to solve the 40-50 m problem (it is only a little bit of space, but in some cases perhaps decisive, like in the recent Midway accident).

3) Now the hypotesis. a) If the fault was technical (very improbable), it should be at the level of the interface or of the software. It should be discarded a mechanical locking of the TL, because the FDR don’t show statements in this sense. b) In the case of the human error, it is probable that the “one TL forward and one backward” procedure, more tricky and unusual, can mislead the pilots when acting under stress conditions, because it is probably stored in the medium-long term memory and not in the short term like the usual ones. The accidents at Taipei and Bacolod seem to confirm this hypotesis. It should also be investigated more deeply why at least three pilots did the same kind of mistake. Were they acting on the basis of the same logic, and what were it?

4) From the safety point of view, some lessons have been drawn and some improvements, as seen, are now implemented. Since it is impossible to revert the flow of the time, it is of little worth to say for example that AI could make mandatory the persistence of the warning “retard”, or that TAM should be more rigorous in the training of his pilots, before the accident. The important thing, is that the chances of the repetition of similar events are at present very lower than after the Taipei accident.

Originally Posted by BOAC Whatever else, the aircraft left them with no real options to stop APART from closing the T/L (if that was the case) and that to me is WRONG, be it Boeing/Airbus/Embraer/Tupolev or whoever - WRONG. Plain and simple. Indeed, if Boeing have now gone that way, then I think they are WRONG too and I would not be surprised if folk are now looking rather carefully at what they have 'created'.
Forgive me if I have missed it in previous explanations - IF there had been those unlikely multiple failures in the sensors and with No2 T/L actually at IDLE but indicating CLB, what could the crew do to deploy the ground spoilers?
5) I ask myself if some form of “total stop device” like the ones present on locomotives, that stop immediately the engines and apply the maximal brake power to the train, could be useful on planes, specially when pilots are not aware of what is really going on, or forget something (as AA 1420 in Little Rock)
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