There does, however, remain a worrying airworthiness issue.

The enquiry has revealed that improper washing techniques can allow water to penetrate the alpha sensors leading to a multiple sensor failure.
A multiple failure will not be correctly interpreted by the automation and in this case apparantly caused a control law change and a full-up elevator trim which was not immediately apparant to the crew.

Complex failures of this kind are difficult to diagnose and indeed are difficult to design around. I find it worrying that a simple error by relatively unskilled ground staff can lead to such a situation.

Alpha limits should never be triggered in normal airline operations but the protection is there for good reasons and there remains a possibility that the failure could be repeated with disastrous results.

Strict supervision of washing operations is the obvious answer but a redesign of the sensors and pilot awareness are also important.

Another case of the world inventing a better fool to defeat a supposedly foolproof system.

JC and Geek, again; the intent of this flights is to make sure everything is working.

An experienced Test/Acceptance crew(Pilots and Flight Test Engineer) is assuming anything can go wrong at anytime.

This crew allowed the speed to decay disregarding the minimum speed at which they should have discontinued the test. When this test is done, that is the absolute minimum speed at which this test is flown.

G

CONF iture;
I believe they are saying that, in normal law, the sidestick demands a load factor, and the commanded load factor did not require more than neutral elevator.

I agree that the presentation of the FDR data, and the explanations leave much to be desired. Which parameters go into the FAC's calculation of gross weight and CG, why are the calculated limit speeds a function of AoA? IMO the report ought to show at least the FDR data on which BEA's calculations are based. See the Australian report on QF72 for an excellent presentation of FDR data.

regards,
HN39

Exactly. Improper static port protection technique during washing can cause false static pressure indication, lot of false warnings, crew disorientation and hitting the ocean. You don't need Airbus for that, Boeing 757 will do. Welcome to aviation - where no task, no matter how trivial it might seem, is to be taken lightly.

Almost. You don't need multiple failure to puzzle automation or "automation". Sometimes all it takes is one sensor giving false data, instead of having good manners and ceasing to function altogether. Single blocked pitot of B757 doesn't cause BLOCKED PITOT light to turn on. Rather it will throw RUDDER RATIO and MACH TRIM false alerts at pilots. Those who go troubleshooting nonexistent failures while putting the lying ASI in charge of autothrottle can easily stall the aeroplane. Single radalt of the 738 that measures zero while being in the air, can reduce thrust to idle on approach and that can be disastrous if the crew doesn't pay attention. Single malfunctioning AoA probe can trigger the stall warning and make the crew trained to always respect the stick-shaker try to re-land L1011 immediately after the lift-off and wrecking it in the process.

Subtle failures can often be recognized only by the intelligent entities. Computers, no matter how sophisticated, are still very far from being intelligent.

Control law change was effected after the aerodynamic stall. Only when the aeroplane started tumbling did the computers "recognize" something was terribly wrong and threw in the towel.

Instead of elevator trim, A320 uses trimmable horizontal stabilizer. That THS can easily overpower the elevator is the piece of basic aeronautical knowledege that is sometimes forgotten. It shouldn't be. Pages 80-82 of the report refer.

HN39,
That is correct and that is what actually happened, but I can see a major BUT here :
The load factor demand law is absolutely inappropriate to a high AoA situation, it is NOT the way the system has been engineered by Airbus. Under normal law, when the AoA becomes greater than alpha prot, the system switches the elevator control from normal mode to a protection mode in which the AoA is proportional to the sidestick deflection. It simply did NOT happen here.

The crew had to recover from a stall situation by using the usual load factor demand law, something that Airbus itself had probably never tested before …

The technical options adopted by Airbus are unbelievably complex, and one cannot realize or foreseen the consequences of deteriorated data as sent to the system and how this all concept of flight control laws and protections will interact.

The BEA, as usual, is silent on this …

Alpha prot would also have stopped autotrim. Unfortunately alphaprot was never activated because the 'polled' AoA's were frozen.

BEA suggests that the erroneous limit speeds should have alerted the crew, although actually they may have misled them into believing there still was some margin to go towards stalling. See Dutch report on Turkish crash at AMS re reading the speed tape numerically.

regards
HN39

The key point here is that they were not conducting a TEST of the system...they may have been misled by the incorrect depiction of the protection limits on the speed tape, but if they had considered a negative outcome to the 'test' they would have had ball park speeds noted- as soon as it became apparent that the FAC speeds were too low in comparison they would have had to resolve the ambiguity.

They were 'DEMOing' the kit and the kit failed - there was no plan B.

Ultimately human error again, unfortunately. Airline pilots, even TRI/TREs are not test pilots. I'm a TRE and I've spent this evening in the sim with two test pilots. Their training and their capacity to critically analyse a system is very different from mine.

Hi,

Do you see that in the BEA report ?
And what about the analysis of each reason panels ?
Why focus on the lastest (cockpit) ?
If any of the foregoing is eliminated .. the accident is unlikely to occur.
Has the BEA in its recommendations will eliminate these panels?

http://i53.tinypic.com/sfxttu.jpg

...for very obvious reasons which are very well documented in the report.

...or considered probable. It's all very nice to preach about need to install the Big Red Button that puts the beast into direct law. Issues here are a) whether it is realistic to expect the flightcrew to recognize exactly what's going on and react promptly b) whether misuse of manual override represents greater hazard than automation malfunction (e.g. some aeroplanes have no manual ground spoilers extensions to prevent their airborne deployment by mistake). Nevermind the control laws, the crew succesfuly recovered from the first stall. Second stall precipitated by full nose-up trim was fatal.
I don't find them unbelievably complex but that's just me. There's no need to predict the behaviour in details as long as the crew recognize it as undesirable and avoids the precursors to it - unless you're doing hard EGPWS or windshear escape there's no need to go anywhere near protections while flying the electric passenger jet. Freezing of the AoA propbes has happened before and test crew stopped the test when no autotrim cut-out was observed at calculated speed.

Because it's where the buck stops and buck's braking action here was severly poor.

Not sure we are reading the same report, but the copy I've got has extensive discussion on the flight operations issue (regulations on these type of flights - or rather lack of) and the qualification of the sensors themselves, and the change in flight control laws.

Of the 6 safety recommendations, only 1 is for the crew, and that is regarding approach-to-stall training. I think that is justified - this isn't the only recent case of a stall recovery being messed up. Nor is failure to correct pitch-up trim an airbus-only problem in stall recovery.

Even that recommendation is not really critical of the crew, given that the recommendation is regarding training, and that the report specifically states that the approach-to-stall procedure was followed.

Dunbar, let me correct you; they were conducting a TEST of the system, it is called Low Speed CONF FULL.

The TEST is to reduce the speed(1 KT/sec), wait for ALFA FLOOR to activate, cancel it; note when AUTO TRIM stops and then stabilize the aircraft at V ALFA MAX for a speed reading, prior to this TEST they must calculate(normally done by the Flight Test Engineer) the minimum speed at which to STOP THE TEST and never go below it.

The crew was not trained to do this TEST and very important, they did not have a Flight Test Engineer on board, a key part of any Flight TEST.

G

They may have intended to do a test (should that be TEST) but their mindset was that that of a demonstration ie they did not expect the test to fail and they did not have gross error figures of the alpha protections which would have given them a heads up of the failure.

So, whilst they were supposed to be conducting a test, what they were effectively doing was demonstrating alpha floor at low level.

I hope that clears it up

Cheers Jon

I get your point, understood.

By the way, the intended test as per Airbus PATM is to verify not only Alfa Floor, which is canceled immediately but also Auto Trim stop, Alfa Prot and Alfa Max. That is why is so important to have the calculated absolute minimum speed before the start of the test.

G

Hi,

Infrequentflyer 789

Indeed .. and the report I wanted to read was .... :)

http://i53.tinypic.com/sfxttu.jpg


HOW? :

Loss Control A320

WHY? (Depending on model REASON chronological order):


Bore hole in the plate "builder" technology choices

Bore hole in the plate "feedback": 2 events prior untapped

Bore hole in the plate "maintenance": non-compliance procedures

Bore hole in the plate "cockpit": low-speed tests carried out in an improvised manner

What Do Pilots Do?
 

Isn't that what the pilots were supposed to do during the test? :ugh:

Recoverable?
 

The uncontrolled pitch up scenario is familiar to me from an emergency procedure on another aircraft and this procedure may well have utility (with suitable modifications) on a wide range of transport aircraft (The pitch trim systems are similar). I am providing this procedure strictly as a discussion tool to stimulate thought and not recommending it for any aircraft type.
From the A-4 Natops Manual (Please ignore the partial disconnect details)

Amen Machinbird...
Sad for me as I read thru the pages of this thread and some of the official reports. Not being familiar with the airbus, I can only guess that the immenently qualified instructor pilot, TRE occupying the left seat was just used to his airbus taking care of his handflying duty of trimming the aircraft during attempted recovery from their low speed condition. Don't recall if the various bank angles were pilot induced in an effort to get the nose dow, or if they occured as a result of low speed aerodynamic forces...tho I suspect the latter.

Not wishing to go back and read the info available, I don't believe the pilots briefed what to look for on their flight displays or what messages to look for on ECAM (or whatever AB calls it) or what to expect or procedures anticipated in the impending recovery drill. Indeed sad that the chain of events leading to the catastrophe included the freezing of two of the AOA probes, and no direct warning to the pilot/s. Apparently there WERE subtle clues displayed, I think, "use manual trim" but it seems no briefing was conducted to actually watch the instruments.
I pointed earlier the pilots complete disregard for ATC speed constraints/assignments in any timely fashion, outright false statement of speed to the controller; which points ME to a nagging doubt that they had any clue about their speed as the Captain slowed the aircraft in preparation for the final event.
I wished from day one in airliners on the 727 for an actual cockpit AOA guage. What would be the harm, say one clock style guage with diamond pointers superimposed one over the other for each AOA sensor. I know, AOA information is only useful for the accident investigators reading the flight recorder data. Needs to be kept secret from the pilots. I don't think the pilots of the accident aircraft would have seen an AOA indicator on their final mission however. Perhaps an AOA indexer on the glareshield?
Yes, the AOA is displayed I believe with the various color bands on the speed displays, but I think they are calculated on 1 g flight. Actual AOA is dynamic and changing for various g loadings, ahh the good ol' stick shaker.

SKS777FLYER,
I see you have flown with AOA before. If the crew had such a gage in their panel, the accident wouldn't have happened despite the Flight Control System locking out the one good sensor. A normal scan of the panel would have showed the problem with the AOA sensors before they had slowed significantly.

The procedure from the A-4 is basically a stick and throttle procedure. It is there to keep things from going out of control until you can figure out what is happening and execute corrective measures. It is somewhat relevant because the A-4, just like virtually every subsonic jet airliner, has a trimable horizontal stabilizer which can overpower the conventional boosted elevator.

Only one problem. The procedure is counter-intuitive.

Natural inclination for a surprise pitchup during acceleration is max power and raise the gear to maintain energy. What is needed is to slow the aircraft back down quickly below the speed where it begins to pitch up. In an aircraft with Airbus style protections, it is probably difficult to get enough wing down to help prevent the nose from climbing.

Could the accident pilot have used this information to successfully save the day? Probably so, if he had trained for it. If he had not trained for it-probably not. It is really very counter-intuitive.:uhoh: Particularly if you have just scared yourself by stalling your aircraft.

Don't Trim Into A Stall!!!!
 

One of the first things taught in U.S. Navy flight training is to not trim into a deliberate stall. Yet, the crew let airplane do exactly that. They had sensor failures but, again, they weren't alert to that. They apparently didn't even know what the stall speed was at their weight and when they approached it, they just kept on going. The AB flight control system can "protect" against some things but clearly not against faulty AOA sensors. The mission of this flight required real thinking pilots but there were none, at least not in the two front seats. :ugh:

Smilin Ed

Just a quick question. You say the USN trains not to trim into a deliberate Stall. Did you mean inadvertently, or deliberately? I might sound pedantic here, but as a training issue, once all the other parameters are in place, including sufficient altitude to recover, why would an assist from the trim wheel be out of place? Especially across all types in the Inventory?

bear

In the 30 years I participated in recurrent training (ugghhh) at AMR, we did many many aproaches to stall in the simulators. Most usually, the instructor (sim instructor or CKA) would have the trainees level at perhaps 10,000 feet, handflying the sumulator. No auto-throttles. The sim instructor would set the power very low and tell the pilots to leave the throttles alone until the first indication of impending stall (ie, stick shaker) and not to trim the simulator. The recovery was to shove the throttles full forward/ ask for max power, keep the wings level, minimize altitude loss and fly out of the situation. The same thing was repeated in a left or right turn; trimming as necessary.

If a type has been demonstrated to have acceptable stall recovery techniques when trimmed for initial speeds X through Y prior to slow down for a stall, but either not demonstrated OR demonstrated to have marginal or unacceptable characteristics when trimmed at speeds closer to the stall, it would be prudent to restrict training to the already demonstrated range of acceptable trim conditions.

Obviously the Part 25 regulations specify such a range, but it may be that on the specific type or types a similarly restricted range of trim conditions was applied.

Deliberate Stalls
 

Others have already addressed this, however, when a pilot is learning about the stall characteristics of a particular airplane, he should trim for some speed higher than the stall speed in the configuration under examination. That way after the stall, or approach to stall, is experienced, the pilot needs only to let go of the controls and the plane will fly itself out of the stall. If you trim into the stall you might have a hard time getting the trim back to an acceptable level, particularly when the trim rate is slow. That's what happened here.

Poor training philosophy
 

Hello

Very bad training philosophy, imho.

If you teach stall recovery, teach it in realistic conditions.
In conditions less than ideal, in a context that includes some equipment malfunctions and/or pilots mistakes : those are the usual pre-conditions of a real accidental stall ...

If you demonstrate approach to stall recovery in "ideal" conditions, where is the interest? In ideal conditions, you won't approach stall ...

Instead, go as deep as possible into realistic teaching ... A simulator crash is not a drama ...

A light airplane is a good teaching tool too :
I can demonstrate trim upset in a C182 ... with different recovery options
And accidental vicious spin entry as well. I garantee that!

Bis47

I think that was the intent of my question. I know Smilin Ed wasn't referring to a baseline training syllabus when he suggested that trim avoidance was taught in all training.

Cross type is a bit of an oxymoron, especially when lack of training and misunderstood aerodynamic handling of a specific a/c has recently killed people.

As you say, training approaches differ on the level of experience and sophistication of the a/c in question. A small Cessna may need a full boot of rudder merely to get it to spin in the first place, while a lack of attention to HS trim can get TRE's and C/A's killed in a sophisticated transport. There is no universal training.

An A-4 needs Pitch input to launch. An F/A-18 doesn't allow the aviator to touch the stick at cat-stroke, and until positive Roc.

When the F-18 "departs" the pilot is required to release the controls until the "box" regains aero. An A-4 in departed flight requires pilot input. This accident is more about misunderstanding one's a/c and overconfidence than a/c unsuitability. IMO.

Hi,

Will not search and quote .. but in the FDR analysis .. seem's the pilot (s) regained full control on the plane for a little time (he was again flying normally) and again the plane departed from normal flight ...
So it's seem's the altitude is not the real problem (as the pilot(s) was able to recover) .. but something ;) on the plane make it departed again .......
Just a tought.

"again the plane departed". If it has been discussed, I haven't seen a discussion related to g loading of the airframe and controls location or input/ location discrepant data. What does this a/c do when "protections" cross swords at inopportune times? What does she do when "g" is negative? The last I remember of the report has her leaving the cloud layer at 60degrees n/u. She entered the water n/d, what was the transition relative to Flight Law, "g", and AoA? Isn't that the fulcrum of the discussion? Did someone mention the lack of a published loading trace?

bear

Hi,

From the BEA final report (captures from PDF documents)

http://i51.tinypic.com/71qx6o.jpg

http://i51.tinypic.com/xclvfd.jpg

jcjeant
That something was full nose up trim with the aircraft in direct law.
That was the point of the A-4 Skyhawk recovery procedure 13 posts before this.
The aircraft was recovered to straight and level flight at 138 knots(from memory) but as it continued to accelerate the aircraft began to promptly pitch up, finally getting up to 57 degrees (also from memory). The pitch up was rather quick. The aircraft never regained auto trim although it switched to alternate law on gear retraction.

If the A-4 procedure is relevant to this event, which I suspect it is, the way to recover from this pitch up would have been to immediately reduce power and to slow the aircraft down promptly to prevent the nose from being driven higher. (Imagine doing this just after stalling your aircraft and recovering!) The intent of the procedure would be to gain time to understand what was happening. The trigger for such a procedure would be a pitch up related to aircraft acceleration.

I am fairly confident you do not have such a procedure in FCOM. And I'll wager that if we were to ask a group of Airbus drivers if they needed such a procedure, the answer would be negative.:ugh:

Machinbird,
Many operating manuals direct increase of throttle w/o altitude gain through the shaker, prior to Stall (No Stall recovery is included, there is not supposed to be a Stall). If in direct Law, it would seem the same procedure 'after Stall recovery has been accomplished' might be indicated. With full n/u trim defeated with a return to Alt Law and gear retraction, my question is still, why did the FP "redepart"? Also, was there a "g" limit imposed on his unsuccessful pullup at the water's surface (Alt Law prot?). I've read the reports, and don't 'get' the sequence of extremely odd a/c behaviours. I also don't understand why the pilot should be necessarily frightened out of counter-intuitive recovery after Stall recovery; Flying is flight, at any speed. You are saying he demanded too much "wiggle room"?

perhaps I am just thick.

bear

LOC
 

Bearfoil

the initial pitch up is a direct response to the thrust application, and achieves a rapid pitchup rate being developed. During the pitchup, the pilot inputs full AND SSC elevator input, but the pitch couple of the thrust line defeats the available elevator authority in the full ANU stabiliser position which has been achieved due to the continued trimming during the deceleration which has occurred due to the underlying fault of the AOA probes being frozen from water ingestion through the seals. The aircraft (IIRC... haven't looked at the data for about 12 months...) exhibits lateral instability during this due to aerodynamic stall, coupled in part with the plots lateral control inputs (the system is not designed to be operating in this regime... and this area was the most interesting to assess if the aircraft fully complies with CS25 stability requirements, it being evident from a number of cases that the FBW aircraft can end up in aerodynamic stall contrary to the design specifications of envelope protection. A conventional control aircraft is required to achieve particular lateral stability and control requirements in a stall, whereas the certification of a FBW aircraft that "avoids" stall has alternative compliance criteria....)

The aircraft pitches up due to the out of trim condition and achieves a very low speed, high pitch attitude, but at a moderate AOA, until it finally runs out of energy and starts to fall off with both roll and pitch excursions, with initially increasing AOA. The ensuing flightpath increases CAS, and results in an increase in AOA again, leading to secondary stall... pitch attitude lowers and the aircraft enters a final dive.... with increasing CAS and increasing AOA again...

To regain control the crew needed to reduce the pitch up couple ie reduce thrust, or trim the stab forward from it's extreme ANU position (11u?... memory fading...), and lower the pitch attitude, possibly by rolling off. Ailerons are low effectiveness (and the data showed possible roll reversal IIRC... which is not too good for a CS25 certified aircraft... :( ), and judicious use of rudder sounds nice but is rather nasty in a swept wing jet transport (do not take the simulators behaviour in training as being representative of the control derivative in the stall regime... data from various events show that the aircraft can achieve very high roll rates ie 5-6 times higher than normal control authority when in a stalled condition). Judicious may be a great term in a subsequent inquiry but it is hardly precise in a high oscillatory loading, dynamic upset event. refer FAR25 CS25, and AC25.7A.

Power reduction at low altitude in a low speed condition is not going to be foremost in a pilots mind... and the rapidly deteriorating flightpath (which additionally result in g loads in the cockpit that are not simulated in any FFS) results in a high cognitive workload, and a likely massive spike in stress levels in the crew. The oversight of the trim state is not a surprise, and has been evidenced on numerous occasions on various types, (the A310 being over represented, as well as the A300-600...)

Humans are a bit like democracy, a lousy program, but far better than all the alternatives... The crew didn't go out planning to have a bad day, but the circumstances they were placed in technically coupled with their unfortunate ad-hoc attempt to achieve a desired "mission" goal placed them in a rapidly deteriorating situation where the time line, workload and stress resulted in their being unable to recover the SA that they had lost in the commencement of the procedure.

Any perception that aviation is a simple task fails to understand the facts of the physics of flight. The routine nature of RPT makes it easy to underestimate the underlying demands of operating high energy machinery in varying environmental conditions with varying levels of system serviceability.


Would think it appropriate for AI to add a CWS voice command such as: "MANUAL STABTRIM REQUIRED" or similar for degradation to direct law, instead of the fairly anemic ECAM messages which were patently not cognitively effective on the day.

RIP.


FDR

- I cannot see how you can defeat basic aerodynamics? Roll reversal is a given, surely?

Rather than introduce another audio input into a by now highly stressed cockpit (what happens to the audio senses during stress??) why not adopt my suggestion of reminding the crew that they are trimming too far n/up (requiring an 'over-ride' action) BEFORE it all goes to pot? Quite a few of our recent pitch/power couple events might have been avoided.

Patterson on Auditory Warning Sounds, Phil. Trans. Roy. Soc B, April 1990

PBL

fdr

Thank you for a remarkably explicit and concise summary. I'm sure it's been covered, then, the occasional conflict between a complex system and aerodynamic basics. Without correct and basic information, situations arise rarely that challenge the pilot's training and experience. Masked over ports, hornets, birds nests, and moisture still plague the endeavour. I am somewhat curious about how the pitch/power couple and bunk trim did in this pilot.


bear

reversal certification reqts
 

Hi BOAC,

the immutable laws of physics exist however (roughly speaking) the certification reqts can be met by good design, or alternatively by a system that guarantees that the exposure to the condition does not occur....much....

As Richard P. Feynman wrote on the Challenger disaster:

"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled."


Feynman's Appendix to the Rogers Commission Report on the Space Shuttle Challenger Accident



The stall speed is defined as the minimum speed reached during the maneuver, except for those airplanes that require stall identification devices (see paragraph 29b(3)(iv), below).
(i) The pitch control reaches the aft stop and is held full aft for two seconds, or until the pitch attitude stops increasing, whichever occurs later. In the case of turning flight stalls, recovery may be initiated once the pitch control reaches the aft stop when accompanied by a rolling motion that is not immediately controllable (provided the rolling motion complies with § 25.203(c)).
(ii) An uncommanded, distinctive and easily recognizable nose down pitch that cannot be readily arrested. This nose down pitch may be accompanied by a rolling motion that is not immediately controllable, provided that the rolling motion complies with § 25.203(b) or (c), as appropriate.
(iii) The airplane demonstrates an unmistakable, inherent aerodynamic warning of a magnitude and severity that is a strong and effective deterrent to further speed reduction. This deterrent level of aerodynamic warning (i.e., buffet) must be of a much greater magnitude than the initial buffet ordinarily associated with stall warning. An example is a large transport airplane that exhibits “deterrent buffet” with flaps up and is characterized by an intensity that inhibits reading cockpit instruments and would require a strong determined effort by the pilot to increase the angle of attack any further.
(iv) The activation point of a stall identification device that is a strong and effective deterrent to further speed reduction. Paragraph 228 of this AC presents guidance material for demonstrating compliance of stall identification systems with the regulatory requirements of Part 25 of the FAR.


d. Stall Characteristics.
(1) Background. Since operational pilots may not be required, or trained, to fly to an angle of attack beyond that for stall warning, any exposure to the behavior of the airplane in an actual stall would be both unexpected and unfamiliar. Therefore, to assure a safe and expeditious recovery from an unintentional stall, it should not require any unusual piloting technique to successfully demonstrate compliance with § 25.203, nor should it require exceptional skill or repeated practice by the test pilot. The behavior of the airplane during the stall and recovery must be easily controllable using normally expected pilot reactions.

Section 25.203(b) states that “the roll occurring between the stall and the completion of the recovery may not exceed approximately 20 degrees” for level wing stalls. In level wing stalls the bank angle may exceed 20 degrees occasionally, provided that lateral control is effective during recovery.

The definition of adequate controllability is specifically described in the context of abnormal aerodynamic configurations:

“Adequate controllability” means that it is possible to produce and to correct pitch, roll, and yaw by unreversed use of the flight controls, and that there are no uncommanded airplane motions due to aerodynamic flow breakdown. If stall warning is used as the end point, then it should be demonstrated that the airplane is safely controllable and maneuverable when flown at the recommended operating speed.

Curiously, there is no testing reqt for the out of trim case to look at the condition that occurs in a stall recovery with trim/power set in an adverse configuration, nor is there an A-PC HQ evaluation required in this case. It would appear that the potential to place the A320/A310/A30-600 out of trim with large thrust couples would be worthy of evaluation, given the adverse outcomes that have occurred (B737 on occasion as well...).

FDR

Despite all the fine quotes, fdr, I will doubt you (or anyone) will ever manage to change the roll properties of a fully stalled conventional wing - as someone once said "for nature cannot be fooled"

@BAOC - true, the key then is to attempt to prevent that fully separated wing stall from occurring. Getting part of the wing to stall, while keeping other bits flying, in a fashion that both warns (deters) further AoA increase while retaining the control to recover the aircraft is the basic goal of any naturally stalling wing design.

Since some people do achieve such naturally stalling wings for certification, and others manage to place their stall identification or deterrence devices (e.g. stick pushers) at higher AoAs than the onset of the aerodynamic stall, clearly it can be done.

The problem is that there is a basic and unavoidable trade-off between prevention and cure. The human body is designed to avoid falling, but once you go off that cliff human's don't sprout wings. Likewise, a bird is designed quite well to deal with falling but doesn't have many features to prevent it from falling in the first place.

The problem then is that as you increase the complexity of the systems to prevent that wing from stalling you also increase the risk that when that prevention fails (and it will inevitably fail sooner or later) there is no cure left.

Mother nature cannot be fooled and one thing it's foolish to believe is that you can design a perfect system. It's always a question of trade-offs, of robbing Peter to pay Paul.

I agree with fdr. If you get into an aerodynamic wing stall in the lower altitudes recovery should be possible by first not overusing thrust and using elevator and stab trim to get the nose down again. I believe it would work in all the Boeings I have flown. Never flew the bus.

Hi,

Seem's for this particular Airbus it unfortunately not worked