Originally Posted by mm43
the PF effectively spent 4 minutes battling with a compromised yaw damper that contributed to the roll and at no time was the SS left in the longitudinal neutral position. Without regurgitating the stuff long since posted (many times), if you simply don't know, the result will be equally simple.
I might be wrong but that's not the way I see it. Yaw damper works as expected and only starts rudder-wagging when aeroplane is stalled and at low forward speed so chances are yaw damper was not compromised mechanically but rather by inefficiency of fuselage-blanketed rudder. Is there something I'm missing?
Originally Posted by HazelNuts39
Probably turbulence: Transition from updraft to downdraft could very well create sufficient reduction of "gee" to satisfy the "gee" demanded by a moderate nose-down SS input, without immediately dropping the nose.
No can do. What you wrote is widespread and utterly wrong understanding of way Airbus FBW works in pitch in normal and alternate laws. Sidestick neutral iz not 1G it is 0G. Yes, you have read it correctly: sidestick neutral is zero gee. "You are pulling our legs!", you probably think. After all, whole lot of Airbus publications, FCOMs included, clearly state: "With the side stick at neutral, wings level, the system maintains 1g corrected for pitch attitude". It is so and it is true. So where is the catch?
Catch is that the sentence I've quoted is often understood to be the description of the principle on which Airbus FBW operates. It is not. It is the description of end result.
Sidestick command does not order G in absolute terms. It adds G demand to already measured, therefore if hit by updraft giving you 1.3G, pull on the stick that would give you 1.1 absolute from straight and level will now result in 1.4 pitch up. Push giving 0.9 would now be 1.2. Same goes for coordinated turn induced acceleration. In other words, stick G command is superimposed on measured level on normal acceleration. Why would anyone make so complicated flight controls system, Because...
Originally Posted by BOAC
When I move a control I expect a proportionate response in the desired direction.
...and that's exactly what you get with such setting. You might be commanding G instead of elevator movement but command sense is strictly conventional: stick down - nose down, stick up - nose up, lest gods of aerodynamics decide you have trespassed over AoAcrit and take away the lift from your wings, that is.
What our esteemed PPRuNe colleague has described as his own experience is what you would get if G command were absolute. In real life it is possible to achieve such a net result only with: severe malfunction of inertial reference, severe malfunction of flight control systems or severe turbulence. Until the time our honourable PPRuNe colleague decides to quit his incommunicado status and shed some more light on his story, I'll file it under "unreliable".
Originally Posted by BOAC
- the more we think we discover the worse it gets!
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For heaven's sake - are you serious? Where have we gone wrong? (Answers on a postcard, please).
You, and I'm using "you" here in strictly plural sense, have gone wrong when you started believing very good sounding but flawed theories that resonated with your prejudices. Don't worry, it's basic human limitation.
Originally Posted by idle bystander
I was under the impression that the reason I trusted my life to the people at the pointy-end was because they were like me, shared my fascination with things aeronautical, and had both the interest in and the knowledge of just what it is that keeps them up there amongst the clouds.
No. We were lured into spending shed-loads of money on CPL training, believing that once we graduate, large pay for short work hours and lot of time in downroute hotels with attractive, young, available and free-minded hosties await us. To this end we have learnt all JAA thinks we need to know about aerodynamics, which can be summed up as: BBDEA - AACED - DAADC - ADEBA. Alas, there was no pot of gold at the end of the rainbow so lucky few of us slave away on pay that leaves one on half ration, after paying off the installment of training loan. You know what is the worst about it? I am not being as sarcastic as you presume I am.
Originally Posted by idle bystander
Somebody please re-assure me that I'm wrong; that what NARVAL wrote, and what was so warmly applauded by quite a few 'pilots' on this forum, does not represent the average level of expertise of commercial pilots, that most of them do actually understand what keeps them in the air, because otherwise I'm sticking to sailing!
Comfort can be always taken by scrolling the page all the way down and reading the big red script. Works like Prozac, if not better.
Originally Posted by Retired F4
BEA only tells us, that the flight control inputs in the simulator produced comparable outputs to the flight controls and caused comparable flight behaviour. Nothing more, and nothing less.
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Where does it leave us then?
It only proves, that concerning the flight control system the aircraft had no malfunctions and that another A330 with the same crew (or with a different crew performing the same inputs) at the same place in the same environment would have ended in the drink too. This recognition might cause more headache for a manufacturer than finding the cause in one faulted part.
You have summed it up brilliantly: any A330 with same malfunction and same control inputs would do the same. Therefore, no mechanical or electronic surprises were present. Why would that cause more headache for manufacturer, beats me.
Originally Posted by OK465
So that although the movements of the control surfaces were consistent with pilot inputs throughout the entire event, there is no direct statement of finding to the effect that after the aircraft exited the flight envelope the aircraft longitudinal movements were still consistent with these pilot inputs even though control surface positions were. Nor does this appear to imply anything further.
AF447 was the first A330 that achieved such a high AoA - basically it went into uncharted territory. That's why sim BEA's sim assessments stops short of going into extreme AoAs. You might theorize and test scale models ind wind tunnel until the cows come home, there's no replacement for testing the real thing to know whether all the theory translates smoothly into practice. Why no test were done at 40° AoA with real aeroplane? Dangerous. Expensive. Unnecessary.
Originally Posted by HazelNuts39
That statement presupposes knowledge of the aerodynamic characteristics outside of the envelope where these characteristics have been established by flight test, perhaps extrapolated using wind tunnel data. Once these characteristics are known, it would not be particularly difficult to model them (at least for the longitudinal motion), and to use them in a simulation to produce your statement.
I realize you were talking hypothetically. To set the record clear who might not understand: such a test will never be made.
Originally Posted by AlphaZuluRomeo
On the other hand, I've never heard of a pilot "taking the time" to trim up (manually) his aircraft while "fighting" an upset, worsening it.
There's always first time:
Tarom A310, near Orly on 24 SEP 1994
Originally Posted by gums
I look at the Airbus protections and laws and am impressed by how many are related to attitude versus AoA or even gee. The pterodactyl FBW system I flew 15 years before the A320 was AoA dominant. At low AoA you could get to 9 gees, but as "q" decreased, you hit the AoA limit and the gee available reduced until it was one gee, So at 25 deg AoA we flew at one gee with stick all the way back, regardless of our trimmed gee. And I point out that we trimmed manually for gee using the collie hat or the trim wheel. So we could trim for zero gee and if we let go of the stick the jet would try to achieve zero gee ( neat feature to gain energy, called unloading). Our trim limits were about - 1.4 gee and + 3.4 gee. The Airbus doesn't work this way.
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I was blessed by a system that didn't care about "autopilot" type limits such as attitude or roll angle. We had no limits on that. It was all gee and AoA and rate limits. Not "protections", but "limits". So we lived or died using the cards we were dealt. And the rules were simple. I don't see this with the Airbuss control logic. Sorry for all the folks here that fly the plane. But that's the way I see it.
I don't think I really need to repost pictures of A330 and Viper. One is passenger aeroplane, other is designed for combat. Every time my name came up on flight order involving A320, it was to move passenger & goods from A to B, if safely possible. Never was I ordered to strafe, bombard or intercept anything when strapped to A320 seat, which incidentally did not have rocket below seat pan or parachute packed in the headrest. Therefore, it is pretty safe to assume that design & certification criteria of two aforementioned superb machines (each in her own court) diverge wildly. Airbus logic is all about passenger transport. To repeat the lesson: stick free Airbus is flight path stable, not 1G chasing. As for G and AoA protections, principle is the same on F-16 and Airbus: full pull back in normal law will give you 2.5 G till AoA max is achieved.
Originally Posted by gums
Lastly, and for those who have not flown to the limits and beyond... If the wing camber does not have a decent washout, then the wing stall will progress from outboard to inboard. This results in movement of the center of pressure forward and actually reduces dynamic stability more than static stability. Hence, it becomes harder to get the nose down. It also reduces aileron/spoiler effectiveness.
Correct but pretty irrelevant to AF447. There was nose up moment from elevator. There was nose up moment from THS. There was nose up moment from underslung engines at high trust, yet the nose was mushing around 10°ANU. If the moment counteracting those wasn't pitch down of stalled wing, I really have no explanation what it could be.
Originally Posted by gums
I strongly disagree with the loss of AoA "protections" when airspeed is FUBAR.
Protections are lost because there is no simple way to compute whether airspeed or AoA is wrong. Stall warning remains, as the detection of aeroplane's energy state and associated decisions now is unloaded on intelligent entity, which must determine whether warning is true or false.
Originally Posted by gums
After all, the jet is in "direct law" until liftoff, isn't it? And then switches to "normal" law.
Correct.
Originally Posted by Machinbird
The feedback channel he had used all his flying career was no longer available. He was operating open loop.
That would be very damning, if found true. Proper way to perform instrument flying in civil aeroplane is by visual reference to instruments, not to column/stick position. Taught from day one of IR training. That's why no one made a fuss about non-backdriven sticks on Airbus. At least no one not anonymous.
Originally Posted by rudderrudderrat
The crew probably never "felt" the stall - they only observed the effects of it then remained in denial and disbelief.
If they relied more on their hearing and sight, and less on their feelings, supposing they relied on anything at all, the outcome could have easily been different.
Originally Posted by rudderrudderrat
Is the difference because it wasn't a requirement due to the low probability?
Way around. It was not trained because of low probability but because it was believed that proper training in: aeroplane energy management, dealing with approach to stall and good aeroplane's stalling characteristic (for the cases where crew really needed time to gather their wits) would make occurence of extreme AoA stall in a passenger transport aeroplane so unlikely as to be unworthy of consideration. Both pilots of two man crew getting so confused to do almost everything wrong was beyond scope.
Originally Posted by DozyWannabe
"Don't fight with the stick; If you feel you overcontrol, release the stick.". It's pretty much accepted that the FBW Airbus setup requires a slightly different technique to get the best out of it compared with more conventional aircraft, but the methods to do so seem pretty well nailed-down, though I'm sure that it takes a leap of faith to release the stick under certain conditions.
It does not. Stick forces notwithstanding, Airbus is pretty classic about airplane-pilot coupling. First time I've heard the phrase "stick-stirring", it was not related to Airbus but Let L-13 Blanik.
Originally Posted by Machinbird
A crew not recognizing a stall! That just should not happen. Particularly with the amount of time they had at their disposal to recover.
Originally Posted by GarageYears
But what was really "wrong"? Training. Training. Training
While I might agree, I'd advise caution not to slip into conjecture. First 3 reports are heavy on technical side while HF side is seemingly neglected, which comes as no surprise to me as it is much more difficult and time consuming part of the investigation. Human are not machines, which sometimes comes as mixed blessing. While aeroplane doesn't care what time of day it is, human beings tend to perform better at 10:00 AM than 04:00.