@Dani
What did i write?
I described exactly what you now say, but did otherwise in your statement. It does not trim for force, but for loadfactor.

In former non FBW systems it trims for force, trim eliminates the force on the yoke.

I hope, i didn´t run into my personal language barrier here.

franzl

Retired F4 done writ:
Nope, I understood you perfectly the first time! :ok:

HN39: Exactly. :ok: :)

We can only hope.

RetF4: The autotrim is not a pitch rate augmentation system, it is a follow-up. It does the same thing as any aircraft trim system and trims out dynamic pressure that would tend to alter the pilot's pitch command. Dynamic pressure has to change to result in an automatic trim change just as would occur in your F-4 (or mine) to clue you that you needed to input a pilot actuated trim change.

It does not trim for load factor, it trims for force (Q) which would alter the pilot commanded load factor or the existing flight condition load factor if the pilot was either not inputting a command (SS neutral) or unable to change the existing flight condition load factor with his command.

Totally agree with you, Dani.
When I proposed that the (nose up) auto-trim should be inhibited if S/W in ON, it's not because I felt the auto-trim performed wrongly.
I see this feature (inhibition) as a supplementary "protection" against a worse upset. History teaches us that, sometimes, pilots do the wrong thing, specifically they pull when (nearly) stalled. No pilot in his right mind will do that, but still that happen.
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.

Then:
Provided the aircraft knows its current AoA (and knows it's too high), I think the aircraf should inhibit the NU autotrim.
With a 100% proficient crew, who reacts as soon as the S/W gets ON, this feature is of no use, I agree.
But with a less proficient crew, who for whatever reason delays his recovery actions (namely: nose down stick, idle power), the inhibition of the nose up auto-trim has 3 advantages IMO:
1] when, hopefully, the crew asseses that he's stalled and engage the correct recovery, the aircraft will be "less" stalled (lesser AoA) than it would have been with the "help" of a more NU THS. The recovery should then be quicker. That means higher, too. Perhaps, the difference in height will be enough to prevent the crash.
2] being "frozen", the THS won't (silencely) change the aerodynamics of the aircraft at a time when the crew may be trying to assess "what's going on". By not "discretely" changing a parameter (and subsequently the aircraft behavior), the inhibition of the THS may help the crew to asses just that.
3] in the event of a further command law reversion (i.e. alternate law to direct law, or alternate law to abnormal attitude law) which will totally disable the auto-trim, the crew will not have to think "hey, I did the wrong thing just earlier, and pulled my aircraft into a stall, let's push the stick and not forget to unwind the trim because auto-trim was available as I pulled, but is no more active now that I push because the aircraft switched to direct law".

All those reasons are tiny holes in the cheese, and of course are less important (IMO) than a crew performing the right action when confronted to a stall (warning). Nonetheless, clogging those tiny holes may perhaps save the day, one time. Then if there is no crucial disadvantage to do so, why not implement it? ;)

Cheers
AZR

PS: By the way, I just learned that USE MAN PITCH TRIM is not displayed in abnormal attitude law (in an A320 at last). That too is a "flaw" IMO.

The endless disputes regarding the niceties of G Load versus its application to Elevator and THS demand is getting rather tedious.

http://oi40.tinypic.com/slpdh1.jpg
Remember - same in NORMAL and ALTERNATE LAWS.

Nowhere have I seen a mention of anything different in ALT2, therefore why would the THS not supplement the G Load demanded by the Elevator to maintain the pitch effectiveness of the Elevator?

AoA versus Gee, once again
 

Salute!

Decent explanation of the trim, OK.

OTOH, I don't think Retired thot the trim had anything to do with rates. And he can jump in here to clarify.

It is true that the trim acts to reduce the pilot input to maintain either an AoA ( older planes) or a gee ( at least two FBW systems I am familiar with). And the amount of elevator deflection or THS position will be adjusted accordingly. Am I good so far?

So am I off-base assuming that a constant gee command of, say 1.15 gee for a 30 deg bank turn with none of the "normal" laws in effect, would result in the THS gradually trimming to reduce the pilot's requirement to hold a bit of back stick?

Sounds fine to this old dinosaur.

But then I note that AoA protections ( I prefer "limits") are lost in ALT laws when there are problems with the ADR subsytems. So I can understand trimming by the system or manually by the pilot that could result in the jet exceeding the stall AoA.

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.

As far as the THS contributing to the prolonged stall? I would think it hurt, but was not the primary factor. As Doze discovered in the sim, the elevators had sufficient authority to get the nose down.

I strongly disagree with the loss of AoA "protections" when airspeed is FUBAR. If the initial pilots did not complain about the 60 knot value or even unreliable speed values, I understand. OTOH, I cannot understand why the "q" was not augmented by a simple WoW switch. After all, the jet is in "direct law" until liftoff, isn't it? And then switches to "normal" law. Or am I mis-reading the FCOM's and other manuals I now have courtesy of several here?

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.

too much verbiage, and remember that I started as a dinosaur and then evolved into a bird, heh heh.

THS response ...
 

OK465,

My own understanding would tell me that RF4 is correct, but I could not prove you wrong either, maybe YOU are correct ?

How things are working in my opinion :

• The input is full fwd stick in ALT LAW
• The request is for a load factor below 1G
• Both elevators try to honor that request with a down deflection
• THS under autotrim command will try to neutralize that initial elev down deflection
• As no change in the load factor takes place both elev quickly reach full deflection
• THS keeps moving in a ND setting but at a slower rate still trying to neutralize elev deflection
• Until effect eventually takes place

What I don't get in your view is that nothing can happen until trim is manually moved, and so in ALT LAW when autotrim is active and therefore USE MAN PITCH TRIM is NOT displayed. If you are correct and I did understand you well, there would be another serious question directed to Airbus.

Quote:Machinbird
Ninety-nine point nine nine nine percent of your flight time or more has been in Normal Law. Just because your regular autotrim has been so sweet doesn't mean she does not have an ugly sister.
Hi Dani, the reason I called Alt2 autotrim an ugly sister is that it deceptively behaves exactly like in Normal law, but has no limits other than physical ones. Nothing more.

When a pilot is mentally confused about the practical meaning of Alternate law, as the PF of AF447 appears to have been, then it is more dangerous if the trim does not stop when commanded a particular direction until it reaches the physical limits.

Think about how often you have seen your trim approaching the physical limits in normal operation (assuming you feel the need to monitor it). Almost never, and definitely not in cruise no matter where your cg is.

I agree that the PF pulled the nose up into the stall using the elevator, and the THS only slightly helped the stall entry since it was perhaps about 1 degree (above cruise setting)during its run for the upper limits.

I have seen evidence in another accident report (DC-8) where the crew brought their roll control inputs to a higher priority than pitch control although they were testing the stall warning when they got into trouble and should have known that the source of their roll control problems was excessive AOA. When the shiny side starts to point down, you airline guys tend to give that a real high priority, don't you?:}

I believe that the PF for AF447 did do something similar. He over-controlled the roll and trusted Mother Airbus to handle the AOA while he sorted things out, forgetting that he was in a different Law where Mother Airbus had passed all responsibilities to him. He almost got away with it, except that when he finally began to get the roll and then pitch under control, the stall warning sounded and a fresh round of wing flailing began as the TOGA thrust (and excessive aft stick) sent the aircraft out of the envelope. The heavy buffet that must have resulted was another thing that must have increased crew disorientation.

PF's eventual adoption of full aft stick was an attempt to damp the bobbing of the nose of the now stalled aircraft (In my estimation.). By this point, he was in full panic mode because the controls were not responding properly. Logical thought was an impossibility.
The THS was quietly running nose up while the crew tried to make sense of this strange land and had the effect of trapping the aircraft in a deep stall. If it had not run nose up, it is not certain that a recovery would have been effected during one of the attempts by the crew of nose down stick, but by being trimmed so far nose up, it became a virtual barrier to recognition of how to escape the stall.

AZR, looks like we are in agreement.:ok:

MM43, this should answer your question. Earlier speculation regarding possible disabling of pitch trim when all airspeed inputs are invalid is another additional possibility, but is not at all proven/demonstrated.

I mentioned an aspect of control input yesterday that I am not sure the majority of you picked up on. Once the aircraft is stalled, the control inputs do not have much influence on the aircraft, and sometimes act in a contrary fashion.

The elevators became fully biased 30 degrees nose up while the PF was attempting to control the nose bobble by holding full aft stick. Once the PF tried lowering the nose, he also continued to try to control the pitch (and roll) rates of the aircraft with the stick so the frequency of his control movements was much higher than the response frequency of the elevators. We have called this stirring mayonnaise and it is definitely a bad technique.

Now the A330 pitch and roll control system does not provide feedback to the cockpit flight controls (stick). If it was an older non-FBW aircraft, the stick would move in close relation to control surface position. The only way for a pilot to know the control surface position on the FBW Airbus would be to observe it on a cockpit readout (but PF wasn't looking there).

The aircraft's attitude indications on the PFD don't follow the stick any more.
Although PF is making significant nose down inputs, he is also making significant nose up inputs. To actually start moving the elevator from its full up position past neutral toward nose down requires sustained nose down inputs.

PF is thus clueless about the net effect of his total input on actual elevator position. We can see the average control inputs pretty easily on the DFDR readout, but the PF could not. The feedback channel he had used all his flying career was no longer available.:( He was operating open loop.

Salute!

c'mon. 'bird.

Whatthehell are you talking about?

We haven't had "real" control surface feedback for 50 years.

And I don't understand all the rest of the last post.

Following the autotrim arguments - it all seems a bit tenuous to say the least. A trail of clotted cream perhaps?
Reading the interim reports again one can find no suggestion of this as a possible factor. I would submit that the only reason the stall was entered into and continued was the PFs actions. We have a known shock reaction for pilots - pull back on the stick and then a series of psychological effects which continue the action. Reread the third interim report (I admit it is harrowing reading) and it is clear that there was panic and a lack of understanding not a problem with the autotrim. Remember autotrim can be turned off by moving the trim wheel. There is no evidence that the pilot even touched it. Once again we are pushed back to training and lack of professionalism.

C'mon Gums. Didn't the stick move as you trimmed your F-101 from fast down to landing speed? :p Doesn't matter whether you are supplying the force to move the whole control surface, or just the force to move the input arm on a hydraulic control valve. That movement is feedback.

I have personal experience with the subject when a small electrical box hanging by its wire bundle began to block the pushrod leading to my stabilator control valve (mounted on the hydraulic ram). I could feel the contact when I flew slow (but not when fast). If that box had moved 1/4 inch further, I wouldn't have had enough nose up to put the flaps down and land back aboard ship.

The point is that on the A3330 as (Old Carthusian likes to remind us) your feedback path is visual from the PFD when hand flying the thing. But when the aircraft stalls, it basically stops following the stick, so you have no real idea of your control surface position without actually looking at the control position display. Does it make sense now?
Better yet, try looking at the control surface position (elevator) versus stick position plots at the end of the 3rd BEA report.

Salute!

No problem, 'bird.

Until some of the dinosaurs here have flown the full FBW systems with all the limits and the coded limits by sfwe and firmwe and such, it's hard to explain.

Ya gotta "feel" it.

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 am disappointed by the lack of training concerning stall entry and recovery, mach buffet detection without the computers advising you, complicated control law reversion sequences, disregard of AoA when the speed sesors go south, and the beat goes on.

Make no mistake, all here, I do not absolve the 447 crew of major screwups. But I also feel that the basic design/implementation of the system should be very clear as to the absolute limits of the jet and not provide the crew with seemingly endless/annotated exceptions to the basic jet control laws they use for 99.9% of the time.

Sorry to become emotional, but I can sympathize with the crew to a point ( like a minute). Then I question their training and experience with critical flight dynamics.

To wit:

- flying with marginal delta between overspeed and stall at high altitude
- recognition of high mach buffet versus the effects of turbulence
- failure to realize that nose could be up, but the jet is stalled, and vertical velocity should provide an indication that something is awry

gotta go

Gums, when you compare what we learned about actual aircraft handling compared to what is presently being taught in the puppy mills, it is night and day. Our training had a price however. Not counting the cost in Jet fuel, and bent aircraft, some of our peers did not survive it,

The whole thing is a cost-benefits tradeoff, but it seems to this old coot that it has gone much too far and seriously needs to become more comprehensive and balanced.

A crew not recognizing a stall! That just should not happen. Particularly with the amount of time they had at their disposal to recover.

feed back
 

Hi Machinbird,
I agree.

The familiar feel of the control surface displacement with control yoke (or side stick) is completely absent on AI FBW. e.g. If you take off with a strong crosswind, the aircraft may roll rapidly shortly after lift off unless you make a roll input. That roll input could be tiny - but the control surface deflection would be large to satisfy the commanded roll direction. So if we have no idea how much the control surfaces are moving in response to the side stick inputs we are making, we have no way of knowing when we are getting close to control surface saturation (max deflection) - (unless we display the Flt/Ctrl systems page).

The crew probably never "felt" the stall - they only observed the effects of it then remained in denial and disbelief.

Q. How many Airbus crew have actually taken the simulator to the stall buffet in ALT LAW? (before AF 447).
How many of you have taken your conventional aircraft simulator beyond the stick shaker to the buffet?
Is the difference because it wasn't a requirement due to the low probability?

@ Machinbird (re: #369)
Thanks :)
But I didn't write the first sentence in the quote you attribute to me ("So autotrim only slightly helped putting the aircraft into a stall, but then effectively became a barrier to stall escape.")
I'm not sure the autotrim was a barrier to stall escape (I understand "barrier" as something wich prevent you (strictly) to escape stall; THS NU will for sure delay the escape, but I'm not qualified enough to say it will prevent it, even if it stay full NU; in fact, my guess would be it prevents not)

Valid points made by yourself and Machinbird - *however*...

At the risk of sounding like a broken record, we have the Stony Creek 727 crash in which all three crew members mistook the shaker for Mach buffet and pulled their aircraft straight into the ground as a result, convinced the whole time that they were in overspeed - ditto the Birgenair 757 Captain. Then we have BEA548 in which a constant stick-shaker and two stick *pushes* were incorrectly diagnosed as false by the crew (who may have effectively been down to the two S/Os at the time). It's a comforting thing to think that if all aircraft behaved as they did in the past that standards would not be slipping and situations like this would be correctly diagnosed, but the stats simply do not bear this out.

mm43's extract from what looks to be an Airbus manual of some kind (I'd love to know which one) contains the legend "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.

For what it's worth I think that airlines should be re-evaluating their training - not just to include manual handling at altitude, but also basic aeronautical refreshers on recognising stall, dealing with stall recovery. If it means having to buy a bunch of Cessnas to do so then they should, after all they're the ones saving money with all this new technology, aren't they? :)

This is an extract from Airbus publication about Unusual attitudes, stall avoidance and unreliable speed, issued in light of AF447.

You can read it also in "A320 family instructor support" by Airbus training und flight operations support division.

There is another widespread misconception that "releasing the stick" means taking off the hand of one's side stick.

It means merely that you shouldn't apply force to it anymore. Leave your hand where it is, you have a nice support there, be calm, see what the aircraft does, check for another input. That's how you should do it.

Someone who hasn't been on the KoolAde diet should develop Machinbird's post #370 further.

The PF input began immediately with a Roll Left and Nose UP. His mayonnaise stirring looks bad, but it is as Mach has said, he wasn't getting input/response sequencing.

Once the a/c balked at responding to PF's first attempt to correct (read the report), he parted ways with the a/c. He became a HUNTER (attitude), not a gatherer. Well and good to condemn, but without the connection hand to craft, the flight path became independent of the cockpit's control.

PNF? He talks a good game, but he isn't in the mix, and I have doubts his results would have been different.

So, after taking control, the PF begins to handle an a/c that is not responding well. He lost the plot almost immediately. The entire CVR is a rehash of every Bus quirk known to man.

What's it doing? The posturers and imposters here are a bit full of themselves. Opinion? I doubt two of three crews could have recovered that flight. The Bus is not a pilot friendly a/c in the stink.

Unstick? And leave the a/c to meander about the sky? What a crock. Damned if you do, dead if you don't. Not a pleasant place, of a Summer Night in the Tropics.

I suppose the Bus Fans have no choice but to condemn this crew. The alternative is to repeat, "What's it doing Now?"

GY, thanks for that informed view.
What I can tell from my experiment is that the trim behaved as it did for AF447.
That was the main purpose of the experiment - I will try more when possible - Maybe he didn't trim down for another reason, we don't know, but he did not.

What I'm curious and nobody came with an answer yet, why the trim did stop short of the UP limit for AF447 ? (He did also in my experiment but a bit earlier around 12 deg)

That autotrim up under stall warning is an aberration.

Like Airbus and the concerned authorities not reacting as needed after the well documented Air Caraibes events is also an aberration. Place every 330/340 crew in a simulated exercice of UAS in CRZ configuration and we are suddenly so more 'clever' if needed.

Reprogram what?
 

Something to ponder?

The thread over the past few days seems to be fairly fixated on autotrim behavior and stick "feel" (or the lack of it, particularly w.r.t. trim). However I think (personal opinion, I'll take the flack) that in any control task, humans are amazingly adept at learning and understanding whatever set of controls we are given (subject to sufficient training/use/learning). What I see here is a collection of folk that have various backgrounds (F4, F16, Boeing this or that, and more) and I think it is fair to say each specific aircraft had unique "quirks". I see comments here related to the lack of trim response on the Airbus sidestick (unlike the yoke crew where trim unloads the force needed to maintain an attitude), but, 'hello!' the F-16 is no different... and in fact I'd state the F-16 is a good analog to the Airbus flight control system, except, more extremely, the F-16 sidestick moves almost not at all - I think the travel is something like an eighth of an inch (Gums?) total. Control is achieved not by waving the stick around but by applying pressure to it. Quite different. Similarly many of us will have played with various flight simulator games... while I suspect many here are gasping in horror at the mention of such 'toys' the point is even with significantly compromised controls (compared to the aircraft) many gamers become extremely adept at controlling the 'aircraft' and can fly the thing pretty much like the plane. What we do is we LEARN. Humans are good at this.

What's my point? The point is we can throw mud at the Airbus control system, but like or not, thousands of Airbus aircraft are trucking around the worlds airways with millions of passengers and they are not falling out the sky any more often that those from other manufacturers. The point is, the crews of those aircraft learn how they work and understand the behavior of trim, just the same way they learn the response rate to a stick input, and so on. Just because that control system is different to Boeing or Embraer or whatever, doesn't mean it is not as good. Clearly it is, since those planes are certified and make millions of flights daily.

You can argue as much as you like that changing this or that is the hail Mary for the aircraft type, but that just doesn't hold water. Does ANYONE seriously think Airbus is going to change the sidestick to provide force feedback for example? The stick currently is force 'loaded' (spring loaded I believe) and I don't really see the need to change that. But others have previously argued otherwise.

So, why'd AF447 fall out the sky, you might ask? Back to something I wrote earlier - "In any control task, humans are amazingly adept at learning and understanding whatever set of controls we are given (subject to sufficient training/use/learning)". This is what went wrong, not the aircraft design. For whatever reason (pitot icing), the automation dropped out, and as designed, handed the aircraft back to the most sophisticated computing devices on the aircraft - the humans. Unfortunately the most important safety device on the aircraft got it wrong. Unfortunately they got it wrong over and over. Zoom-climb (wrong), pulled into a stall (wrong), continued pull (wrong), TO/GA (wrong - but I'll pass on that since it seems this might have been a trained response), lack of CRM (wrong), and so on. Lot's of wrong here.

But what was really "wrong"? Training. Training. Training. With sufficient training the crews response clearly would/should have been different - very much so. Would it be different today - I suspect emphatically "yes". Because this accident has highlighted so many issues, any Airbus pilot worth his paycheck should have been following the accident investigation and learned a massive amount - mostly what not to do, but I'm sure a lot about the Airbus control systems. The key word in the previous sentence = LEARNED.

How did Gums learn to fly the F-16? Hands on the stick and throw the thing around the sky (some in simulators I hope... job security for me!), but NOT hundreds (or thousands) of hours tooling across the oceans on autopilot.... I see so many references to pilots with 11,000 hours (or whatever) and every time my immediate thought is "subtract ALL autopilot hours off that and what do you REALLY have???". Low hundreds perhaps, if we're lucky...

In my book this is the problem. The time when the crew were needed the most, was exactly when the automation took a timeout - and that corresponds exactly to the skill-set the crew has least ability.

So what am I advocating? More hand-flying on the line? Perhaps not - the autopilot is there for a good reason and does a great job. Simply holding the stick for hours transiting the Atlantic doesn't teach much. We need to get pilots into aerobatic aircraft and get their basic flying skills on the edge of the envelope up to snuff - recover from stalls, spins, etc. Then get those same crew into the training devices (simulators, flat-panel trainers, etc) and fail the automation and get their hands on the stick. Create situations where the control laws degrade. Learn Alt Law. A lot of sim time is spent training one engine out situations on takeoff, etc - are the current training scenarios really relevant today - how often do engines fail? I believe that LOC is the single most significant cause of accidents today - not engines failing/catching fire/etc.

Don't get me wrong - if there are simple changes to the systems within the Airbus cockpit that will help, they surely should be implemented (I suspect the stall warning inhibit below 60 knots should be revisited). But the single most significant change is reprogramming the HUMANS who get to sit in the very front seats.

- GY

Mbird - can you expand on please? I am not sure I understand what you are saying and have a feeling I might not want to understand it either.

Gums - - you need to define marginal here, as where they were cruising on the carpet graph is where we all fly - day in day out, and is fine and safe..

Training, training, training
 

Salute!

Thanks for the nice words, Garage.

We had no simulator back in 1979. Didn't have one for another three years, and it was a POS.

We had a very simple FBW system with few "laws" or "protections" compared to the Airbus. Our "laws" were based upon maneuver limits and not "autopilot" functions like max bank angle, restricted pitch attitude, etc. Our "limits" were there to provide max performance while reducing the odds of a ham-fisted pilot getting into trouble.

Our autopilot was extremely limited in its authority. The GD flight control wizards didn't want something getting in the way of their system.

I see the reverse in the Airbus.

I do not want to see airline pilots "experimenting" with the limits of their jets, especially with 200 SLF's in the back. But I would hope that they would occasionally fly some planes that have classic stall characteristics and learn to cope with unusual conditions.

I had just arrived at Hill when we got the word that our neat jet, which could not stall or spin or....., could enter a "deep stall" due to the basic FBW design and the aft c.g. we used. So we saw the films and the test pilot interviews and we were PREPARED for when it happened to us!

We had little, if any, "feel" for mach buffet due to the wing design. So the Airbus crews had a leg up on us. But they also had a small envelope that allows for little error WRT mach and AoA. They had to be "better" than us in that regard.

My feeling is that better training will be the cure, and not a massive overhaul of the FBW system

I did pick up on..... At a quick reading, just didn't have time to confirm in a post. Am not sure how that counts in the flow of things, as those that need read them, and understand them are not those that are in agreement with you, like I learned unequivocally recently. Your contributions in the last several pages were masterful, but that bold last short sentence is a perfect engineering description, that I am most envy of. :D:D:D Thank you.
.

Automation did not drop enough : Leave the trim alone and we have a different game to play.
Then include it in the wrongs ... Why not ?

I think I grasp your delineation.

It may be just semantics, but "delaying", may practically mean "preventing it", when it's part of a complex set of causes of a final fatal outcome.

GarageYears,

I totally agree with your last post. As for myself, I concentrate on "small" technical problems (autotrim, stall warning) because I don't feel qualified to discuss -more important- training issues. Besides, here is the tech log.
The risk is of concentrating "only" on those relatively minor issues, and take them as an excuse to continue to "save costs" on the training...

Yep.

It's been an expensive "lessons learned," hasn't it, this crash of AF 447?

It has cost dearly AF, 228 people and their families, and who knows how many others.

In its wake, it is likely that a good many AB flying folk (and organizations) have delved deeply into their machines and know them better now than they did on May 30, 2009.

To fly your aircraft you have to know your aircraft.

What was it we used to say in the Navy?

NATOPS is written in blood.

Looks like a few things have not changed yet ...

From the git, AB has been marketing complexity as dependability, and "Ease of Operation" as simplicity.

Both are utter lies, and errant horse----. Training needs to start at the Line, and I don't mean the AIR Line. The Production LINE.

To require pampered pilots to inherit a wild thang in the worst of circumstances, without some history of mitigation/preparation, is manslaughter, imo.

My opinion, and we'll see what France thinks.

Wolf, I appreciate your experience, but flying the line is not Blue Water.
Nor should it be. These babies are not Ace Sixkiller, nor should they be.

They are Lambs for slaughter, 447 case in point.

AZR, I apologize for including a sentence you did not author.:O It seems the wonders of the Windows operating system require great care to avoid posting stray cat and dog comments in conjunction with those you intend.
If I clarify my definition of a barrier as an impediment that can be overcome with some degree of difficulty, I think you will see that a we are still in agreement regarding the import of the nearly full nose up trim.


No, I don't think they are going to change that anytime soon. My point in posting the lack of feedback in the stick is merely to explain the "open loop" control condition the PF faced once the aircraft stalled. There was no convenient feedback path for him to know what kind of control displacement he had actually requested. This was primarily due to his extremely rapid mayonnaise stirring control inputs. If he had made and held a control input, then the surface would eventually catch up to his demand the way it did in the nose up direction. The rapidity of his control inputs well exceeded the ability of the control surfaces to respond.

Quote:
Once the aircraft is stalled, the control inputs do not have much influence on the aircraft, and sometimes act in a contrary fashion.

BOAC, I am probably not telling you anything you don't already know. Once you stall you will likely find that your control inputs may have a reversed effect in the case of roll (due to adverse yaw), or that the surfaces are relatively ineffective and the aircraft's motions due to vortex shedding and cross channel aerodynamic coupling mask the effects of your control inputs. The elevator inputs are masked by the THS input and likely a post stall phugoid like effect results (a nose bobble). To have an influence, you need to make a control input and hold it or in the case of roll, you need to use the rudder and lay off the ailerons.
http://images.ibsrv.net/ibsrv/res/sr...eply_small.gif

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?

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...

...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".

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.

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.

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.

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.

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.

I realize you were talking hypothetically. To set the record clear who might not understand: such a test will never be made.

There's always first time: Tarom A310, near Orly on 24 SEP 1994

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.

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.

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.

Correct.

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.

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.

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.

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.


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.

Quote:
Originally Posted by Machinbird
The feedback channel he had used all his flying career was no longer available. He was operating open loop.

Not really. This is really a Human Factors type evaluation of what the PF had to work with while using his mayonnaise stirring stick technique, and only applies while in a stall. He is not supposed to be in a stall, but it appears that mayonnaise stirring is a particularly bad control technique while in a stall. That might be a lesson we can take from this.

I'll bet there are quite a few engineers that do not agree.

Quote:
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.

Quote:
Originally Posted by GarageYears
But what was really "wrong"? Training. Training. Training

Even the BEA seems to hold the viewpoint espoused by Garage Years and myself:
.

I've been trying to pin down what specific training in my background convinces me that I would recognize the stall in the same situation that the AF447 crew faced.
The two factors are:

1. Having read D. P. Davies description of the deceptive nature of the stall in a relatively level attitude.
2. Having spent time maneuvering swept wing aircraft to their performance limits. (This has already saved my posterior on more than one occasion. Once was in a puddle jumper.)

Hi Machinbird,
I was wondering the same thing myself. The Airbus Flight Training Study Guide (2003) had the following recommendation when in ALT LAW and approaching the stall: (see page 13) http://www.737ng.co.uk/a320training.pdf
"Eventually, the master warning and aural warnings will activate (crickets and “STALL, STALL” ). Recover at the stall warning by selecting TOGA thrust, maintain a pitch attitude for level flight and accelerate through VLS."

Unfortunately, AF 447 crew discovered that it doesn't work at FL 350.
(They probably had it demonstrated at 5,000 ft in their sim conversion course.)

Thank you for your elucidating explanation/correction. I'm amazed how one continues to learn new 'secrets' of the control system after so much time. What you write makes sense to me, but leaves me with a couple of questions:
I've read somewhere that full back side stick corresponds to a demand of 2.5 g. Suppose you are at 1.3 g with neutral side stick, then pull the stick to the back stop. What do you get?
Then we have this description in mm43's post #366: "With STICK FREE in turbulence, small deviations do occur on the flight path but with a tendancy of the A/C to regain a steady condion". Does that functionality only exist with stick free?
Agreed. I've edited the last sentence of my post.

That technique, while patently wrong, would not be lethal if center of the stirring movements were set around neutral or moved forward as ADIs have shown pitch increasing. Problem is that average input was heavy nose-up. That's not ham-fistedness. That's confusion.

They even did not try to set attitude for level flight. How could they discover it wasn't working?

Big part of being pilot is to be able to tell the difference between 5000 ft and FL330. Consequent to that is to know how aeroplane behaves at different altitudes or at least which altitude dependent procedure to apply.

G protection comes into play. 2.5 G slats retracted, 2G slats extended. As for how exactly G demand is related to stick position: me knows not. It felt linear and progressive in the area I have ever needed to use, which was certainly never above half travel, and that was good enough for me.

With stick in pitch neutral; yes. If you move it out of neutral you command flight path change so nose might be bobbing but overall it will move in the commanded direction.

Now you reminded me I have to further qualify my statement that Airbus is not particularly prone to aircraft-pilot coupling; it is valid in still air. In turbulence, tendency of the airplane to self-correct pitch and bank disturbances may (and too often does) lead to pilot induced oscillation. Statement you quoted is mighty correct and is followed by very good advice to avoid large interventions with stick.

At what point did they try maintaining pitch attitude for level flight ? They (or at least PF) only tried pulling up. And they knew it. As someone said earlier on thread: PF responded, "But I have been climbing for some while...."

First:

If this and other LOCs were down to pilots who could handle a conventional aircraft perfectly well in the same circumstances but were constrained/prevented/confused by the airbus flight control laws, then I'd agree - ditch Alt laws and drop straight to direct. Give the crew the conventional aircraft if/when things start going wrong.

...but I don't think the above is a correct assumption. There's a subset of pilots (probably including those who care enough to follow accident threads on here) who would handle direct law just fine (or better), but is that the majority when I also see comment after comment along the lines of Machinbird's "compare what we learned about actual aircraft handling compared to what is presently being taught in the puppy mills, it is night and day".

Second:

I don't think stopping autotrim would have affected this accident. I know you've argued that had the nose gone down they'd have diagnosed the stall, but I'm not so sure. When the a/c did pitch down in stall what was the reaction ? Pull-up, hard. If you're already prepared and briefed for stall in the sim, the nose drop is going to be obvious, but if you think the a/c isn't responding right (which looks like an issue in roll at least even before the stall) and you're pulling back and the a/c suddenly drops the nose, what will you do ?

Third:

Changing something one way to "fix" one accident may make things worse in other cases and end up killing more people. We should look at all the LOC incident history not just this one. I've done some looking, though not in any way a systematic survey, in what I've read the common factors were:

Airbus: no. FBW: no. Sidestick: no. Trim / AutoTrim: oh yes. Time after time. Not every incident, but probably a majority - and much more common factor than the others.

But what is the typical problem with trim, what's its MO when it kills ? Looks to me like it's trim-up before stall, autos drop out, trim not managed by crew then contributing to the upset and/or preventing the recovery. Exactly the opposite of 447 - which looks like the odd one out.

IF789, in the sample of accidents you looked at, as well as finding a common factor with autotrim, do you see a common factor in what has been identified as the problem by more than one expert above – to quote, training, training, training - ?

Chris N

Maybe not, but I can't provide the reassurance asked for. I raised similar concerns myself back here and triggered a well written response from PJ2 here

Could be a lot of reasons for that. PJ2's comments referenced above; increased auto-everything; SPOs and regulation (RVSM) that all but prohibit hand flying; and Glass.

That last one's a huge difference for the non-pilot looking in (and maybe for the trainee starting out...). Look in at the old style hundreds of steam gauges and row after row of switches and be awed, and fearful - you better learn and understand every one of those, this is complicated. Look instead these days at three computer screens a handful of switches and (maybe) a joystick - well, how hard can it be ?

Yet the fundamentals of flight haven't changed, the machine underneath is as complex as ever, if not more so, and the margin for error doing a few hundred knots in an aluminium can at 30k ft is still just as small...