Lyman

Dozy, read what he says:

"I have no control of the plane at all" He wouldn't say that if his inputs were having effect.

Not to burst your balloon, But I don't care what you think, HE thinks his controls have no effect. And, erm....he's flying.

DozyWannabe

But the traces show that his inputs *were* having an effect, and that the aircraft was too aerodynamically unstable for the flight surfaces to have the effect he was expecting.

It's been pointed out more than once that the PF was a sailplane pilot, and as such should have been more likely to understand the basics of aerodynamics than many.

The question he should have asked himself (and his colleague) was "*Why* do I have no control of the aircraft?". The clues were there, and at that point there was still plenty of troubleshooting time.

[The desire to absolve the pilots I can understand (and to some degree is already backed up by their apparent lack of training), but why the continual grasping at straws to conclude the aircraft must have either forced them into making the mistake or suffered a failure above and beyond that we already know?]

gums

first of all...

@ rouli The Viper limiters were inviolable - very hard. The only way to manually control the horizontal tails was with the pitch override switch, and that thing did not work unless AoA was above 30 degrees In other words, we could use it to "rock" outta the "deep stall". I had some excerpts from the Code One article on that in a very early thread here when we were discussing the possibility that the AF jet had an aft cee gee and the same problem as the Viper at extreme AoA's.

@ EMIT TNX for the nice words. I knew about the Belgian, as it was a few months previous. The thing about getting slow or even close to a normal AoA was you lost roll authority. I commented on this during my approach, and 170 knots was prolly too slow, and I should have stayed at 180 or so. The engineers told me that I had approximately one pound to play with out of the 17 pounds required for max roll command. Another factor was that the yaw trim reversed as you slowed down below "x" AoA. So it was a good thing I simply drove the sucker onto the concrete with no flare or attempt to soften the touchdown. That technique became the procedure after another incident or two.

@ Doze Yeah I know the three modes, but feel that the "alternate" should be more basic and eliminate the THS auto-trim feature. old ground, I know and we had a good discussion on the pro's and con's two years ago.

DozyWannabe

As we discussed two years ago, I believe the autotrim shouldn't be the issue because it is one of the things that Alternate Law has in common with Normal Law and as such would feel more natural to a FBW Airbus pilot who has spent 99% of their time flying in that mode.

The only reason autotrim became a factor here was because the PF commanded inputs which were way in excess of what should have been expected in Alternate reversion. The setup in the case of dropping out of Alternate Law is to give the pilots full authority, which makes perfect sense as long as the pilots understand the situation and make their inputs accordingly.

Interestingly (if the sim session was anything to go by) the A320 does have hard limits on autotrim in Alternate Law - which required manual intervention from the TRE to match the trim state of AF447 during our session. Why this was not carried forward onto the widebodies is a question for Airbus themselves, but I wouldn't be surprised it if was a reaction to the perception that the A320 was excessively limiting - if this was the case then the lesson should be "be careful what you wish for".

The point that I still stand by is that a drop from Normal Law means that you cannot rely on the protections and more care must be taken when making control inputs. Alternate Law does make sense, as does the requirement for at least two data sources for protections to be active - I hope you can at least follow my reasoning there even if you don't necessarily agree. The role autotrim played in moving the THS made their lives more difficult - that's a given. But the inputs that caused the autotrim to command that deflection should never have been made in the first place.

gums

I agree with you for the most part, Doze.

Our "autotrim" was referenced to the gee we had trimmed for. So If I pulled hard and relaxed, then the thing tried to get back to the "trim" setting I had. thought we went over this before.

As I mentioned, some folks trimmed to zero gee when entering a fight so to "extend" and gain energy they just had to relax on the stick and HAL got to that wonderful zero gee condition. My understanding is the 'birds on the wing and slot use a tad of trim for something like 0.9 or so. Makes the close up work a bit easier.

Lyman

[The desire to absolve the pilots I can understand (and to some degree is already backed up by their apparent lack of training), but why the continual grasping at straws to conclude the aircraft must have either forced them into making the mistake or suffered a failure above and beyond that we already know?]

1. There are mistakes and failures far in excess of "what we know". Just a stabin the dark.

2. No desire to absolve the pilots. I am asking questions in areas that have been foreclosed by a rush to conclude.

3. Questions I ask are studiedly biased at times to elicit a different look, or pov.

4. I have a place in my heart for "patsies". The "fall guy", the pilot, iow.

Much of my passion here has to do with how absolutely crazy it is that this happened. "Airworthy aircraft, meet certificated pilot crew, see you in Paris."
From the brief prior to launch through "I have no control".... It makes me angry.Most of my anger is reserved for AF. Except the pilot group, who showed stones in demanding a r/r pitots.

The flip side is there is so much to learn, to change, to re-assess, and then re-introduce ourselves to a more honest approach to Air Travel. The driving force morphed from an innocent joy in having breakfast in Paris, and dinner in San Francisco into a numbers game. It would have been alright, but for the greed and sloppy handling of things that cannot be compromised, and must always be held close. We're in this together, and a mild jump in camaraderie and integrity would be nice. There is no relax, in the shop, on deck, or the ramp. Let the heathens choose colors for the FA's uniforms, but keep them out of the equipment, and all its supporting iterations.

This crew is not as derelict as some would suggest. Unfortunately they were a bit shy of what must be a new standard for all of us.

DozyWannabe

Fair enough, but the system you're describing suits a fighter, not an airliner. I hate to repeat myself, but the very fact that in the F-16 the human pilots had the option of ejecting in extremis makes the design considerations of the system as a whole very different.

The investigation seems to be pretty thorough so far and has in part led to the first collaboration between Boeing and Airbus of its type regarding response to stall.

Not to seem rude, but you've enthusiastically backed every theory from vertical stab separation to jammed stabilisers to inappropriate FD commands to try to point the finger at the aircraft.

I've got no problem at all with that, but the outright fiction (e.g "no UAS procedure existed") goes way beyond that, to the point that it can sometimes appear as deliberate attenpts to misinform.

Again, fair enough - but you only seem interested in pursuing a single line of inquiry.

There are no "patsies" in this case (and much as it may drive CONF to distraction, neither were there any at Habsheim). The aircraft was mishandled - the evidence to back that assertion up is overwhelming.

I am relatively certain that there is no drive to "protect" Airbus within the French aviation safety community. I'm equally certain that there never was. Like all other manufacturers, I have no doubt that their legal department is poised to argue the toss if necessary, but thus far there's been no evidence to suggest that there is. The BEA gains nothing from it - so why does this suspicion remain?

I'm hoping you mean Rio De Janeiro or Sao Paulo - otherwise we're talking about a completely different flight.

No-one (not even the DGAC) is suggesting that the crew were "derelict" - merely that the evidence suggests that they mishandled the emergency. There's a big difference.

Owain Glyndwr

Sticking my neck out, but this is why I think that when he said that he was almost entirely correct.

1. With the wing completely stalled, the ailerons would have been useless - no roll control, but maybe some adverse yaw.
2. At that sort of AoA the rudder power would be severely limited because (a) it was working at something like 70 deg effective sweep and (b) it was probably sat in the low energy wake of the stalled wing.
3. The elevators and THS were working.
4. When you roll an aircraft around the fuselage axis at high AoA you get an increase in sideslip and a reduction in AoA just from the geometry.
5. Changes in AoA produce changes in pitching moment and that in turn changes the pitch attitude. So there is a pitch/roll coupling.
6. At high AoA, as I have said before, the Dutch roll changes to a lightly damped or constant amplitude roll/sideslip oscillation. This will be accompanied by a corresponding pitch oscillation. [Check out the traces - the roll and pitch oscillations have similar frequency and much the same relative phasing throughout once the aircraft is stalled]
7. He would not be able to control the roll oscillation - with zero aileron effectiveness no amount of thrashing of the sidestick is going to make any difference.
8. He would not be able to suppress the pitch oscillation by using elevators because the motion would have been perpetually regenerated by the roll motion.
9. No wonder he thought he had lost control!
10. The only vestige of control left to him would have been a steady application of down elevator to reduce AoA, after which the other problems would disappear. Tragically this was the one option he did not try.

mm43

In the period from 02:10:57 through 02:11:38 they may well do, but the results certainly don't. As I surmised in a previous post the CL was hanging on as demonstrated by the synchronized roll/pitch oscillation. So when the PF made the statement, "I've lost control", he had realized that his inputs were having no effect on the outcome.

I see that Owain Glyndwr has made comments complimentary to the above.

rudderrudderrat

Hi DozyWannabe,


The elevator basically follows the sidestick inputs up to 02:10:45 with deviations mostly around zero - which is what a sailplane pilot would expect. Thereafter, the FBW computers are attempting to maintain the pitch attitude requested by pf, despite the speed fall off and well beyond Alpha Max, by applying stab trim and lots of up elevator.

At 02:12:15 down ss has no effect - full up elevator is still applied.
After 02:12:30, despite nose down inputs, the elevator never reduces beyond -15 degs and for the most of the time, both elevator and stab trim are fully saturated at full nose up.

Since the crew were never aware of their control surfaces' positions (unlike a sailplane) - I'm not surprised that pf thought he had no control - because (fortunately) he could not pull back any harder even when he tried.

HazelNuts39

The PF didn't know that at 02:11:32. Until then the plane was still responding in pitch.

That said, you're right about the rôle of the control law. The response of the elevator to sidestick demands depends on the pitch rate and normal acceleration that the airplane already has.

Linktrained

When was Flight Idle selected ( for a few (10 ?) seconds only )? NOW this is said to be a part of the new joint Boeing/AB Stall recovery for aircraft with their engines mounted under the centre line or wing.

IIRC the pitch of AF447 was reduced during this short period, before TOGA was restored and the pitch went back up and remained up.

( For these brief moments AF447 WAS indeed a " stalled glider", with whatever advantages this might or could mean. Think of AirTrans, which was not stalled as I recall, but did fly as a glider to a safe landing.)

As a stalled glider of course the nose should be lowered, to get the wings working properly as usual. And then power restored to make it an aeroplane.

As has been discussed "STALL" appears not to have been recognised.

DozyWannabe

mm43, rudderrudderrat - cheers.

I know that in stalled air that the ailerons would not have had the desired effect, I was just trying to squelch the notion that the surfaces didn't respond.

I'm trying to remember whether the elevator traces are absolute or relative to THS angle, because you can see clearly the elevators beginning to come down when nose down is applied for a few seconds, first by the PF and then by the PNF - unfortunately too late in the sequence.

roulishollandais

@gums, #803 thread 8

Shame to me ! for mismatching the Viper limitations ! Sure it is hard-limited and very well protected inside its enveloppe in normal law.

Connection with AF447 :
@ Dozy
To be master or slave concerns precisely who decides when reaching the limit and the protection at the limit and if you can override it.

DozyWannabe

Those limits weren't plucked out of the air though, they were defined by the test pilots (a group of the best and most experienced in Europe) who went up in the prototype A320 and found them. So the "master" of the protections is still a pilot - just not the pilot in the seat at the time.

CONF iture

Apparently both.
Up to that time the HDG was constant meaning the PF was able to maintain the vertical FD bar in the center, but at 02 11 30 he applies full left stick (even the PNF is 'helping') but the HDG is increasing, the vertical bar cannot be maintained in the center ...

(…) je n’ai plus le contrôle de l’avion là
J’ai plus du tout le contrôle de l’avion

No control in roll
No control in pitch

I'm not able any more to keep the FD bars in the center.

What is terrible about that is that just before the FD bars reappear the PF had finally managed to stabilize the situation.
Sir, you've been criticized so much up to now, you was doing well, well enough to arrive in Paris, I just wish you took a big breath before following those reappearing commands ... I just wish those commands never came back.




mm43, I know I'm asking a lot, could you add to your graph the HDG, lateral inputs, ... in fact all the parameters.
Your graph is terrific, only a video animation would be better.

DozyWannabe

@CONF iture - you sound awfully certain of this. Do you have proof that he was trying to follow the FD or do you just wish that were the case?

If they'd followed UAS procedure the FDs would have been turned off and would not have come back.

roulishollandais

@gums, #803 thread 8

Shame to me ! for mismatching the Viper limitations ! Sure it is hard-limited and very well protected inside its enveloppe in normal law.

Connection with AF447 :
@ Dozy
To be master or slave concerns precisely who decides when reaching the limit and the protection at the limit and if you can override it.

DozyWannabe

Given that the limit is set pretty close to the point at which structural damage or loss of control is possible, why would overriding them be a good idea?

jcjeant

It is nevertheless regrettable that the BEA is not an NGO
His ultimate boss .. is the state
If for some reason .. a survey of BEA threaten the state ... the survey could be classified as top secret .. or state secrets
A perfect example is a Caravelle accident very long ago ...
Another example is the disappearance of a fishing vessel where a submarine is suspected
I don't think the BEA had free hands in those inquiries ... and indeed .. he gains nothing ..