Originally Posted by
airtren
They in fact, fall in the same category with the others, as the ability to recover or not recover does not change the character and source of the problem.
I'm not saying that the behaviour isn't problematic, I'm saying that I don't think that the return of the stall warnings is unambiguously triggered by the nose-down inputs. The only source that suggests that there was internal disagreement at the BEA is that one "La Tribune" article, and as such until I see some corroboration I'm going to be sceptical.
And if you think I'm being stubborn about press accuracy, you wait until you've spent a little more time on this board!
It is wrong to say that the failure of the SW to relay the correct information to the pilots does not matter because it was too late for them to recover anyway.
Again, I didn't say that it doesn't matter (I'm an engineer, I like to find things to fix!), I said I'm not 100% convinced it played a causal factor in this accident
It is bogus, because it was a Stall Warning giving the wrong indication relative to the PF actions
Based on the evidence of a single press article that almost certainly comes from within Air France (which as an entity would benefit financially and in
PR terms from Airbus having to shoulder a larger percentage of the responsibility), I'm not buying that until I see some better traces - right now it looks ambiguous to me.
and relative to the state of the “a/c” relative to Stall.
That's fair - however as I said before, this is the only airliner to my knowledge that has been that far outside the envelope for that long, falling from that high - so at present it's not clear whether there is a deficiency in the stall warning design specific to the A330 (and by extension the entire Airbus FBW range), or whether this is something that needs to be examined on an industry-wide scale.
The message from the PF/NPF/CDB perspective was signaling a transition from NON STALL to STALL, when in fact the transition was from STALL to NON STALL.
Well, not quite - it was still stalled. If the nose-down inputs had been maintained before passing, say, 15,000ft on the way down then it might have stood a chance of coming out of the stall, but that's not a given. Remember that a stall warning is designed to activate before reaching the stall itself, so once it had picked up speed and the wings were unstalled, the warning would continue for a few seconds until it was out of the stall warning regime. That's not bogus, it's just a factor of the design.
Hypothetically, if they had successfully unstalled the wings, started bringing it back under control, but the extra couple of seconds of stall warning meant the difference between successfully pulling out of the recovery dive and crashing - would you be arguing deficient design on the part of the aircraft? Do you think Air France would?
You are missing the point, if you think, that the exact internal cause, or the mechanism of triggering the message matters. It does not matter, relative to the needs of the pilots, and state of the “a/c”.
It matters if you want to think about how to fix it. The guys who designed these systems didn't just slap it all together - everything they did had to fit a very strict set of criteria. There was a reason the logic was designed as it was and as such, any change is going to have to be considered very carefully.
In the same time, you’re making my point – if the internal mechanism was creating the condition in which the STALL Warning went silent...
Well, this is the thing - we've had two explanations doing the rounds - one, that the stall warning is inhibited by a software setting and the other is that once the airspeed has fallen that low that the AoA vane no longer functions. No doubt we'll find out if one, the other, both or neither is true in the coming weeks and months.
Which one would correspond to WSJ, and which NI? Media makes money from disseminating information, and scandals make money….But there is a gauge that each of us has, and in this case it is not the trash, that you could throw a Blanket Dismissal at.
This crash has been under investigation for more than 2 years now, and many following it had the ability to have a good enough understanding without being influenced by one press article, or another.
I don't know if you've noticed yet, but there is a small cabal of pilots, reflected in a number on here who have a kneejerk hatred of anything Airbus. This is in part based on press assertions made since the late '80s that Airbus was a prime mover in "taking pilots out of the loop". Some believe this was a deliberate attempt to deskill the job of airline pilot and undermine their livelihood. This is complete nonsense of course, but the press fed that rumour mill and made it what it is today, which is kind of ironic when one considers the short shrift most pilots give the majority of mainstream media articles on aviation.
I'm not that bothered about people who take the time to understand the issues, but when the press get it wrong, or chase a certain angle to get a juicier story, it pollutes the general public's understanding of the issues at hand, which is why you've still got a lot of people today thinking that the infamous 1988 crash of the A320 was caused because "the computer thought it was landing and overrode the pilot", or that "Airbus makes planes that use computers, Boeing still use good old-fashioned cables and hydraulics in their new designs". This bothers me because regardless of whether related to aviation or not, I can't stand people who should know better spreading misinformation.
What’s the today’s press and TV news in France? More of course... as there is more reaction by the parties involved....
Interestingly at the moment it's Air France that's making all the noise - Airbus seems to be keeping their cards very close to the chest at the moment.
So what if other planes don’t have it. Is the validation of other planes needed for Airbus?
It's helpful to stop the "If it ain't Boeing, I ain't going" crowd from crowing.
But ultimately the subject of Stall Warning is a prickly one - as far back as 1972 you have crashes caused in part because the pilots thought they were getting a false stick pusher activation, dumping the stick push and in doing so sealing the aircraft's fate.
There is one very simple, but also major reason to have it: Operating it in relative secrecy, when the results cannot be easily perceived by the entire team in the cockpit contributes to the type of AF 447 accident.
And there are equally plenty of major reasons not to, not least of which being what would happen if a back-driven sidestick was wired up in reverse during a critical stage of flight (which has happened). Others include the assistance in enforcing SOPs, crew roles and CRM given by having one person with their hand on the stick at any one time, the extra systems complexity and weight that setting up back-drive entails (the 777's backdrive system by its very nature has more potential points of failure as a result).
It has become a matter of personal preference really.
As we speak about this, I still have an unanswered question relative to the Airbus 330 stick functioning:
Is the control surface deflection proportional with the duration of a stick action in a certain position – if it is longer action in a certain position, is the deflection different than shorter action in that position?
In Normal Law you are commanding *rate* of movement in the axis rather than deflection. The FCU will do whatever it deems necessary with flight controls and thrust to get you the rate you're commanding. As you progress down through the laws, channels move from rate to deflection. In that case, I don't think the amount of time you hold the stick in a given position changes the deflection, but obviously the longer you hold the stick in position, the more time that deflected surface has to act, same as any other aircraft.