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EGMA
I think it worth remembering the difference between recovering from an incipient stall and a developed stall. The only 'good news,' though, according to this article covering a meeting that took place this year, is that both main manufacturers, and presumably the airlines too, appear finally to be well aware of the need for a 'rethink':- "Recent crashes linked to stalls include that of the Colgan Air Bombardier Q400 on approach to Buffalo, N.Y. (2009); Turkish Airlines Boeing 737-800 in short final for Amsterdam (2009); West Caribbean Airways MD-82 in Venezuela (2005); Thomsonfly Boeing 737-300 near Bournemouth, England (2007); and XL Airways Germany Airbus A320 off the coast of Perpignan, France (2009). “Most approach-to-stall incidents and accidents occur with sufficient altitude available for the recovery,” Boeing Senior Safety Pilot Mike Coker told delegates at the Flight Safety Foundation’s European Aviation Safety Seminar in Istanbul this year. “Incidents progress to accidents when the crew fails to make a positive recovery after the stall warning occurs.” "Flawed training is partly to blame, he asserts. Approach-to-stall training is typically conducted at simulated altitudes of 5,000-10,000 ft., but many stalls actually happen much higher. In the case of AF447, stalls occurred at 35,000 ft. and 38, 000 ft., respectively. That has important, negative implications, Coker concludes. “Recovery stresses an increase to maximum thrust and recovery with minimal altitude loss,” he says. Therefore, “students try to minimize the nose-down pitch change while engines spool up.” "To make matters worse, engine margins at high altitude are much smaller than at lower flight levels, where pilots can count on a much greater response to power increases. Also, Coker says, “it is probable when pilots remain on a particular model for extended periods of time that their exposure to approach-to-stall indications and recovery occur as infrequently as once in a decade,” when stall exercises should really be part of recurring training. He stresses that training should focus on correct procedures, reducing the angle of attack and appropriate energy awareness, and not so much on minimizing altitude loss. "Airbus and Boeing have worked together to devise new procedures for stall recovery that emphasize angle of attack rather than preserving altitude." I think that tends to confirm my earlier speculation that the blame for this accident is likely eventually to be spread four, or possibly five, ways - in no particular order, the manufacturer (extensive instrument shutdowns, plus the currently-inexplicable behaviour of the THS), the airline (inadequate training and undue emphasis on 'conserving altitude'), the pitot-tube supplier (given that low speed indications may have triggered the stall warnings even though true airspeed may still have been adequate), the pilots, and the weather. The only 'good news' is that the industry as a whole seems already to be reacting to the 'lessons' of AF447 and other similar accidents, not just waiting for the BEA to produce its report. |
mm43;
Originally Posted by mm43, post #1889
You can argue over the simulated paint colours, but the picture of what was happening should be pretty clear. In my opinion, they were not in "severe turbulence" - more like "light chop" with the occasional "bump".
Turbine D, hear you...agree it's weather-related because the pitots iced up but I don't think the weather played any other role in the loss of control. Only thing I would add in response to others' rides through the area is, such weather always changes rapidly and what was for one a turbulent ride with need for wide diversion around buildups can be good ride with light chop twenty minutes later for another. RWA; But you'll know much better than I do that airline pilots hate diverting or reducing speed unless they have to, because it means delays. So I hope that you'll agree that there's little doubt that turbulence was a factor in the early stages of the accident? Diverting or reducing speed costs little time and little fuel...perhaps a two, three minutes and a few hundred kilos. Diversions are not 'hated by airline pilots', they are routine operations when/where required. Unless the diversion is for hundreds of miles off course, (done it), a diversion around weather is a non-issue in terms of schedule and fuel. Notwithstanding sudden surprises, I agree with mm43 that they likely experienced nothing more than light turbulence. The vertical and lateral acceleration parameters will tell us soon enough, along with anything said between the PF & PNF that wasn't released in the recent update. |
Hi,
PMFJI, but I don't think turbulence played a direct role at all in this accident. This "going to right" (despite the apparent correction to left by PF) will continue until plane contact water ..... (BEA graphic) If not turbulences or weather induced .. what is at play there ? |
Maybe simply in his haste to grab the side stick when the autopilot disengaged would easily do that since he was reaching for the sidestick in the dark from the left side of the stick and probably bumped it to the right. Unlikely turbulence would have caused it. So far all we know is they lost airspeed indications so the autopilot and autothrottle disengaged. I am sure his hand was nowhere near the sidestick when it disengaged and with his limited experience in the aircraft doubt if this ever happened to him before this event. Sometimes it is nice to have a big fat yoke in front of you when things go south instead of a meal tray.
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Hi,
Maybe simply in his haste to grab the side stick when the autopilot disengaged would easily do that since he was reaching for the sidestick in the dark from the left side of the stick and probably bumped it to the right. Unlikely turbulence would have caused it. So far all we know is they lost airspeed indications so the autopilot and autothrottle disengaged. I am sure his hand was nowhere near the sidestick when it disengaged and with his limited experience in the aircraft doubt if this ever happened to him before this event. Sometimes it is nice to have a big fat yoke in front of you when things go south instead of a meal tray. From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row. The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS). That's wrong if the BEA note is exact The BEA note show only a "left nose-up input" after the autopilot disengaged .. nothing about a right input by the PF The right bank is uncommanded I am sure his hand was nowhere near the sidestick when it disengaged and with his limited experience in the aircraft doubt if this ever happened to him before this event. Pure speculation not supported by any BEA reports so far ... You can speculate .. you can't be sure (or maybe you had see the FDR ? :) ) |
Originally posted by jcjeant ... This "going to right" (despite the apparent correction to left by PF) will continue until plane contact water ..... (BEA graphic) If not turbulences or weather induced .. what is at play there ? During the stalled descent, the airflow over the aircraft was abnormal and may have been affected by a vortex which developed a geostrophic clockwise rotation causing a pressure differential across the vertical stabilizer. On the other-hand there could have been a non-reported control defect, and if this happened I'm sure the BEA will report it in due course. |
No, JC, I don't know where his right hand was when the AP disconnected but how many pilots on this thread guard the side stick during cruise? I would guess none. I never guarded the yoke because it was so easy to reach and a waste of time. Once in an MD80 I was flying into Atlanta on a cat 1 and below 300 ft in the clouds the plane went into a right bank and AP and AT clicked off. I recovered and landed but who knows what the AP is going to do before it disconnects. That is why we have pilots to fix those things. I can not see any reason to pull all the way back on a yoke because I lost airspeed, can you? Maybe Airbus teaches alpha protection rules that I chose not to learn by not flying it but it didn't work very well this time. Maybe airlines should make sure that their pilots can handle unreliable airspeed problems without losing control as obviously happened here.
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Nose up
It makes no sense why the experienced pilots after stall warnings would fixate on the flight instruments showing a high pitch and low airspeed; then continue with full stick back and watch it unwind to sea level for 4 minutes. I don't buy it. It simply doesn't add up. The stall warning disabling I admit is confusing however the attitude indicator showing nose up is unmistakable.
IMHO they were not aware of the attitude/airspeed or dismissed it as being bogus. The fact that they nosed up and finally reduced thrust to idle is consistent with a perceived overspeed and nose dive attitude. I have not read any alternative hypothesis that makes sense despite interesting discussions about THS etc. :confused: |
xcitation:-
IMHO they were not aware of the attitude/airspeed or dismissed it as being bogus. The fact that they nosed up and finally reduced thrust to idle is consistent with a perceived overspeed and nose dive attitude. I have not read any alternative hypothesis that makes sense despite interesting discussions about THS etc. And I'm afraid that you're just wrong about them continuing noseup inputs. IMO the BEA note is more notable for what it leaves out than what it puts in; but it does at least report the fact that, with more than 10,000 feet in hand, the PF did in fact 'do the right things,' reduce power, and apply nosedown stick:- The altitude was then about 35,000 ft, the angle of attack exceeded 40 degrees and the vertical speed was about -10,000 ft/min. The airplane’s pitch attitude did not exceed 15 degrees and the engines’ N1’s were close to 100%. The airplane was subject to roll oscillations that sometimes reached 40 degrees. The PF made an input on the sidestick to the left and nose-up stops, which lasted about 30 seconds. At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications". At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again. |
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Shore Guy Pitch and Power: Lessons from Air France Flight 447: AINonline Did the Air France crew simply fail to fly the airplane, as some claim, or were they the victims of a training system that taught them to rely too heavily on computers right up to the moment the impossible overload occurred, like the HAL 9000 in Stanley Kubrick’s film 2001? No one questions whether or not the Air France crew met the certification requirements in place at the time they received their type ratings. But does the type-rating requirement on an Airbus, or any other large aircraft, go far enough into the actual handling characteristics of the aircraft–especially at high altitude–and especially when multiple computer failures occur? (Bolding by me) Are those actual handling characteristics of FBW aircraft - especially at high altitude- and especially in Alt or Direct LAW known to the manufacturer and to the regulating authorities, and if known, how are they communicated to the training departements and pilots? Since nearly two years a lot of experts and pilots of this forum (i´dont count myself to those experts) familiar with the aircraft or at least familiar with FBW or engineering FBW are discussing what happens when this and that is going on. Looking back there is lot of disagreement concerning technical and piloting issues, besides the principle PP and importance of AOA. We have searched the web and found uncountable publications related to the aircraft, its normal and abnormal handling procedures, but concerning aerodynamic behavior of the aircraft in high altitude cruise where the ship is flying most of the time, the information is thin to nothing. We know, flying is done by automation, but how and why and by what system seems to be out of the grasp of not only the aircrews. What will the aerodynamic behavior of the aircraft be when AOA exceeds an value, how will CL shift, will there be a tendency of the nose to drop or will it stay high, what will the stabilizer effectiveness be, will ss roll input induce opposite roll due to missing yaw compensation, and how will a degradation of the FBW systems due to failures influence this natural aerodynamic behavior of the aircraft? If some and a lot more points are known to the crew in such a situation, only then wil they be able to judge the effectiveness of control inputs (like nose down stick, how long, how much nose down.....) and have a better chance to do the correct actions. I wouldn´t have survived in my fighter, would i have been trained and tested on such a minimalistic scale. |
Hi,
Yes, this "roll to the right" has been noted earlier and the PF appears to have kept it corrected in conjuction with the NU inputs to the sidestick, i.e. P Maybe the pilot would not act on the joystick if this angle to the right would not have happened I suppose the fact to roll to right induced also a lost of altitude |
Stall vs. overspeed
I've read with interest almost the whole thread. It puzzles me why would a trained crew of 3 experienced pilots not recognize stall and would try to handle the situation with nose up inputs most of the time during the fatal fall.
It seems to me like if the confused pilots would try to handle or avoid a (non-existent) overspeed problem. Now I have a general question: What is actually a more feared situation? Would an unhandled dive lead to kind of Mach 1 speed with a fatal end? Do pilots try to avoid overspeed even if there would be a risk to end in a stall? It is called coffin corner after all... There is a great deal of discussion about stall in this thread over and over but I can't find anything about overspeed problem. Can someone please explain this or point to some link which describes the situation more? |
A List To Learn From
Like others in this forum I suspect that no one factor will be found solely responsible for this tragic loss.
Having read (I think) every post in this thread, as well as both BEA reports, I have tried to make a list of ‘things we should learn from’ so as to avoid a repeat. I would be interested to hear if I have missed out anything significant. Before I get flamed, I should point out that I am not a qualified Aircraft Engineer, my flying is now in the past tense, and these are my subjective opinions! The aircraft appears to have flown into a storm. It is unknown whether the decision not to detour further away was due in part to a fuel constraint. Airbus considered the need to upgrade to the pitots only warranted a Service Bulletin, rather than an AD. This is surprising given the number of documented previous occurrences of unreliable airspeed and their obvious safety implications. Air France appears to have taken over a year to start to implement the SB. AF447 had not been upgraded. A lack of visual and aural cues from the controls (no yokes moving, no throttle levers moving, no “tick, tick” from the HS trim) may have denied the crew warning of the impending AP disconnect. The design of the stall warning system, whereby it is disabled if the apparent airspeed (i.e. as measured by the pitots) falls below 60kts is astonishing, given the known pitot icing issues. It beggars belief that such a system can get through design and certification. The Airbus Stall Recovery procedure in force at the time, which the crew appear to have been following, started with “TOGA”, and had no mention of either getting the nose down or checking HS trim. No distinction was made in the procedure between recovery from an incipient or a developed stall. The disabling of the HS autotrim once in Abnormal Law has apparently been a factor in other accidents; it remains to be seen if it was a factor here. |
Optional vs. Mandatory
Mandatory Service Bulletins are paid by the manufacturer: Thales or Airbus in this case. Optional SB are paid by the user, and on the user's schedule. The maker tends to downplay the urgency, in order to avoid paying the cost. It takes a diligent regulator to correctly accept the maker's determination of mandatory vs. optional.
If an airline wants to incorporate an SB Free of Charge, it often has to argue the case. Pending orders for new planes affect these negotiations, of course. Assuming there was a limited supply of new pitot probes, it would have been prudent to do a phased upgrade, doing one at a time on each plane until the full fleet has one new pitot. Doing all 3 at once on each plane was a mistake, not only for logistics, but also if something went wrong with the upgrade. If just one pitot on AF447 had been replaced earlier... |
Roseland
It is unknown whether the decision not to detour further away was due in part to a fuel constraint".
Well, unknown to you and I certainly, but I bet the answer comes out on the CVR, and is known to the BEA. If started early enough a 20-40 nm detour adds an insignificant amount to the fuel burn. Of course if you wait till you're face to face with the big painting on the radar, it's something else. |
Mandatory Service Bulletins are paid by the manufacturer: Thales or Airbus in this case. Optional SB are paid by the user, and on the user's schedule. The maker tends to downplay the urgency, in order to avoid paying the cost. It takes a diligent regulator to correctly accept the maker's determination of mandatory vs. optional. The decision of mandatory is entitrely the regulators based only on the facts of the impact on safety. The manufacturer may place in the record any needs for urgency as they see fit. There has even been cases where a manufacturer's recommendation for urgency have not resulted in a mandated action by the regulator. This is not about money, it's about safety relative to the original type certificate and any new useage data.About the only time money enters into this is the time for compliance factor. |
Roseland - I go with all of your post #1909 except the para beginning
The aircraft appears to have flown into a storm |
Roseland - I go with all of your post #1909 except the para beginning Quote: The aircraft appears to have flown into a storm which is totally unproven. AF/IB and others diverted, to the east............... They flew straight into it.............. |
They didn't fly directly into the storm they deviated west instead of east as did half the flights. They took a 12 degree left deviation to avoid weather. Apparently their pitot tubes froze up because of faulty probes that hadn't been replaced yet. When they froze up they pulled back into a deep stall for some unknown reason and crashed. No data of severe weather, just choppy conditions typical of that area. I hope the final report comes out soon so the nonsense can go away. Pilots all pick their way through weather depending on what is happening at the moment, not what another flight did 30 minutes before them. Weather changes rapidly sometimes.
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