This is by far the most interesting discussion on this site.
Like RWA,I have been going over and over possible scenarios that could have led to this tragedy.
As I see it we have two choices:
a)all available retardation devices were functioning normallly and the pilot was defeated by a combination of i)longish touchdown ii)wet runway iii)tailwind iv)early application of max REV which precluded the rwy GA option(we know they got spoilers from the "spoiler" call-technically,this is the only call a skipper needs before going with max REV on a short wet runway(involuntary action).However,if the touchdown was delayed(prolonged float or incorrect TCH) ,this is reason enough to throw the landing away despite the spoiler call(judgement action).In this case of course,he went for max REV regardless so its not really relevant.However,I think its interesting to mention because it describes a situation where two independent triggers are momentarily in conflict and as we all know the body doesnt always do what the brain actually wants.Very often the body will complete an involuntary action even though it wasnt really what you wanted to do.
b)A failure of the autobraking system to arm followed by failure of alternate brakes OR failure of autobrake system to arm followed by crew switching off ASKID prematurely(ie they jumped the gun and went straight to the NNC-didnt give alternate brakes a chance to work with ASKID).A looming runway end and knowledge that no overrun exists might have induced panic and led to such an error.The evidence rules out spoilers/reversers as being the cause.That leaves some anomaly in the brakes surely...
Some have declared that this cannot have been the case as the decel call was made and MED autobrake was set.But what if the autobrakes were not working and if the decel call was made on PFD trend alone?They had max REV and spoilers so decel might have "appeared" normal in the early stages.Reversers are efficient as a deceleration device in the high speed regime.They would start to become inefficient just around the time things started to appear wrong..ie 70 knots.On a short wet runway,thats an awfully nasty surprise.The warning for it is inhibited until 80 knots??And they did get a status message which the co-pilot wanted to clear??
Then theres the "quitame" call which we learnt might possibly be translated as "switch off.."
Switch off what?The ASKID/NSWSTRG switch ?Could it be anything else?
The Cardiff incident might help explain one or two things.What helped the skipper in that incident was that he used only IDLE REV so the failure of the autobrakes was readily apparent early on.Runway was longer and dry of course.He attempted to recycle(incorrect procedure) the ASKID/NSWSTRG switch after only 1000 feet runway used.In Toncontin,MAX REV was used so if autobrakes were not working,their failure would not have been apparent to the crew either by status mesage(inhibited),PFD trend(would still be healthy),or seat of the pants feel..Dangerous trap.If he had armed MAX,then the discrepancy in actual and anticipated deceleration would surely have been noticed.But because he only armed MED,the autobrake failure could have been masked by max reverse.
Perhaps an experienced and impartial Airbus pilot can answer the following questions:
a)What does the Decel light actually indicate ?
b)Do you call decel based on PFD trend or on the light?
c)how often do you use manual braking above 70 knots?
d)Have the safety recommendations from the Cardiff/Ibiza incidents been truly addressed by Airbus Industrie?Has the switch been renamed ASKID/NSWTSRG/BSCU?Have Airbus improved automated warnings to flightcrews concerning brake effectiveness following touchdown?
e)If autobrakes are used so trustingly and widely by Airbus pilots,should their failure to arm be cause for more than just a status message which can be inhibited by the computer during the touchdown and rollout phase above 80?
Last edited by Rananim; 13th Jul 2008 at 02:52.