PJ2
Thanks. Very comprehensive. I remain a bit of a cynic about whether the AF447 scenario would have been factored into any proving regimen for the Airbus flight control laws testing and certification. The intangibles presently are:
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...a. The non likelihood of any assumption, for trials purposes, of all three raw data pitot sources becoming simultaneously compromised (which is after all
the likely unforeseen circumstance and unintended consequence leading to AF447's downfall)
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...b. The prescribed failure hierarchy can be short-circuited sometimes. i.e. if it's anticipated that A will fail then B then C etc, any non-alphabetical scrambling of that design failure's graceful degradation sequence can become a true "spanner in the works". (I'm trying to think of an example here. Maybe somebody else will). There are a few EFIS systems around that have test switches labelled "maintenance only" (but accessible to flight crews) that can do weird things if cycled inflight. I can also recall some oddball induced rollback failures on the Allison engines of the Electra (if you were to pull certain DC circuit breakers on the TD system). These were never documented but then again, if that CB had tripped spontaneously (i.e. wasn't pulled), you then knew "why". Same unexpected failure modes if one phase of a triple-ganged CB was to trip in a hydraulic system; knocks out a fan, leads to overheating etc.
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...c. The postulated sequence of events (in my scenario) would have the AF447 crew just not noticing the insidious developments (small increments of trim and thrust over an extended period). I've flown a few aircraft where the autopilot was capable of holding quite significant force gradients (BARO HOLD in but autotrim disabled and manual A/P trim being utilized). You had to be careful when disengaging or you'd break legs down the back.
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...d. I'm reminded of the 1994 break up of Shrike Commander VH-LST upon autopilot disengagement and severe pitchdown. Bendix analogue device for sure, but I've also experienced some strange autopilot behaviour in other types.
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I'm finding it hard to envisage a force feedback system within FBW that could run the auto-trim to null - and so I've "punted" that it is FCPC dictated by the resolved CAS. So, until I'm proved conclusively wrong on that, I don't consider that you can readily discard the possibility of the THS being trimmed to a position inappropriate to the actual airspeed of that A330..... and it possibly being a factor in what may have happened at autopilot disconnect. Just as in the A320 accident off Perpignan France, there are some unanswered questions about the Flt Control system's conduct once boundaries are being challenged..... although compromised AoA sensors are likely to be the culprit there.
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SaturnV said:
The ASJ is not published by a dis-interested party. For example, the Nolan-Law Group, publisher of the ASJ, in Chicago is presently suing Parker-Hannifin, asserting that its equipment was responsible for the crash of EgyptAir 990. They are also suing Air France for AF 358 for the weather-related over-run at Toronto.
Actually David Evans of ASJ (ex Air Safety Week Editor-in-Chief) is very independent of Nolan Law. No-one at Nolan Law vets his stuff. He is sometimes tasked by Nolan to research accidents and does so with ex NTSB Chair Jim Hall (and others of the same ilk in the air safety business). PJ2 may be one of these consultants for all I know. However DE never writes those accidents up on ASJ after the tasking event. That's mainly because by the time litigation comes around, it's really no longer newsworthy. I'm not DE but I know him and he is fiercely independent and has a long history in aviation safety journalism.
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