Originally Posted by
deSitter
Oh boy this is an understatement. There aren't many chapters in aviation history as sad as this one. One finds oneself grasping at straws to understand it
Based on the information we've had over recent years, it's not that uncommon an accident type (now that more basic errors and systems failures have reduced in number). Night operations are the worst possible time and place to have unreliable instrument indications - being in the vicinity of convective activity only adds to the risk - certainly something that would weigh heavily on the mind of any pilot in that situation, regardless of experience, age, type rating or temperament.
Originally Posted by
Ashling
That said if they had responded correctly to the initial stall warning would they have found themselves in that situationand having found themselves there they had other indications, attitude, to help with the diagnosis. A pilot well versed in UPs/Upsets should have been able to recover the aircraft safely.
Originally Posted by
kilomikedelta
Checkboard; Would the cockpit displays tell the pilot that the THS was at maximum nose-up so that stick aft wasn't helping?
The attitude indicator/"artificial horizon" would have been telling them exactly what was going on in that regard. However, as has been shown by accidents over the last 20 years, how pilots react when instruments become unreliable is heavily dependent on their aeronautical knowledge and temperament. In the case of the Birgenair 757, only one pitot tube (the Captain's) was blocked, and all other instruments including the F/O's ASI were indicating correctly. Despite this, the Captain seems to have almost shut down, focusing on his erroneous speed indications despite the F/O clearly warning him that his own instruments indicated that they were stalling.
The question is - given that you know at least one instrument has failed, how much are you willing to trust the others? In this case you're in the middle of threading your way through some dicey weather conditions in the middle of the night, so you have no outside reference, and as has already been pointed out it's around 3 minutes from the onset of stall to impact with the ocean (it took me longer to write this paragraph).
Originally Posted by
mm43
Not least is the lack of coherency in what has been reported by the BEA, which I believe is possibly a deliberate attempt not to put any party in a bad light, and also to placate while side-stepping any judicial implications.
Or possibly, you know, just releasing information that they can confirm completely at this time rather than releasing information that needs time to be double-checked and re-checked. In their position would you rather go with what you know and can prove, or go off half-cocked and possibly have to issue an embarrassing retraction at a later date?
That said, thanks for the link - this seems to have some relevance by my reading (emphasis mine):
In Alternate Law, Valpha prot and Valpha max are replaced by VSW. Note that VSW is a stall speed and so is EAS sensitive unlike Valpha prot/max. Stick free aircraft aims to control alpha by limited authority stability order to less than VSW. If the stick input forces VSW exceedance, alpha floor activation of TOGA occurs. However, it is possible to stall the aircraft as the protection may be overridden. Above V/Mmo an over-rideable nose up demand is introduced. The VSW symbol disappears but Vmo+4 and Vmo+.006 warnings remain. V/Mmo is reduced to 305/330/.82.
Alternate 2 : Pitch control laws are identical to Alternate 1
Originally Posted by
RetiredF4
Can somebody explain, how tis is done in relation to the airspeed? I mean, at high airspeed the change of the trim for a given stick input would be slower and at low airspeed it would be higher?
What kind of speed input does the system use, the wrong one from the iced up pitots? If that is the case, in the beginning the actual speed was still high, but the sensed speed was wrong and already much lower.
If I've got this right - the system will detect the unreliable speed indications and simply give the pilot the authority requested (in this case full nose-up or thereabouts). Loss of airspeed indication basically implies stall protection is minimal, if not lost entirely in this failure mode.
[EDIT: Just checked - autothrust was disengaged early in the accident sequence. With autothrust disengaged, stall protection in this mode is indeed non-functional. At Habsheim, we saw a demonstration of what Normal Law will do to prevent stall in the event of autothrust disconnect/disable - i.e. command elevator inputs to maintain incidence even if the PF attempts to command nose-up. It would appear that Alternate Law in combination with autothrust disconnect defers to pilot input (as designed).]
Originally Posted by
CONF iture
No Paul
and Airbus thinks it is just fine ...
Really, CONF?
Originally Posted by BEA notes
At 2 h 13 min 32, the PF said "we’re going to arrive at level one hundred". About fifteen seconds later, simultaneous inputs by both pilots on the sidesticks were recorded and the PF said "go ahead you have the controls".
Looks like he was perfectly aware from where I'm sitting...