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HWell Bobn, can you provide some more detail on what you did?
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In the Boeings you have to work at it to keep it stalled, but we were doing a falling leaf, descending at 11000 ft/min, 10 degrees nose up at firewall thrust. |
Would the recovery have been easier without thrust ?, it depends on geometry but those underwing engines are likely to generate a nose up tendency.
most assuredly yes... |
Let's say you have a properly trimmed airplane that for some reason gets into a nose-high attitude and begins to fall as AF447 did. Is there a regime in which you just cannot get out of it? Will the nose always come down if you have proper trim and take the thrust down to idle if necessary? Is there a danger of entering a flat spin? How to avoid that?
I keep thinking some sort of emergency reaction control to push the nose down might work. Some small solid rockets just for emergency use. |
I keep thinking some sort of emergency reaction control to push the nose down might work. Some small solid rockets just for emergency use. |
Is there a regime in which you just cannot get out of it?
some t-tail jets, the BAC-1-11 had a famous one during flight testing, have deep stall tendencies, where the horizontal stab is rendered useless...in an airplane with a conventional horizontal stab, it seems impossible, provided sufficient altitude is available to recover...even the 727 was found to NOT be prone to deep-stall tendencies...in the AF crash, it appears no positive effort was made to recover from the stall...simply lowering the nose down 5deg is not sufficient to reduce angle of attack to below stall when the aircraft flight path is much greater..Airborne Express DC-8 on a test flight is another example of flawed stall recognition and recovery training... |
Trying to avoid the dreaded Pprune edit nonsense, but I would like to append my earlier post to reinforce that there still needs to be a greater focus on training and making sure the pilots really know how to fly the airplane by hand and understand basic aerodynamics. I've seen so many industries lose their way on fundamentals, and I would like to see the aviation industry avoid that. Too many lives are at stake.
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At the risk of waking the Oozlum bird who has managed the odd 5 minutes sleep here:
As far as we know: 447 was kept in a nose-high attitude by a) a nose up demand on the sidestick b) TOGA c) Full nose-up THS delivered by the software and sidestick demand. Whenever either a or b was relaxed, the nose appeared to drop. I think it is safe to assume that had the stick been held forwards and the power reduced it would have recovered (given sufficient altitude). This appears to have been a 'foreign' concept to AB pilots at the time. |
I keep thinking some sort of emergency reaction control to push the nose down might work. Some small solid rockets just for emergency use. |
Originally Posted by BobnSpike
(Post 7296817)
In the Boeings you have to work at it to keep it stalled
In the sim experiments we did, you had to really hold the stick back to keep the nose where the crew had it - because as the speed bled off, the nose clearly wanted to come down. Even with the THS all the way back, it was possible to recover using forward sidestick alone - which we did as we came back down through FL320, during which time the trim wheel obediently rolled back forward - and come out of the descent at around FL180.
Originally Posted by BOAC
(Post 7297129)
c) Full nose-up THS delivered by the software and sidestick demand.
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AF447 Lottery
AF 447 crashed because the pilots allowed it to stall. The pilots allowed it to stall because they pulled back on the stick. They pulled back on the stick because they were confused. They were confused because the automation left them in the lurch. The automation left them in the lurch because of a mechanical problem with the speeder tuber thingies. The speeder tuber thingies failed because they got clogged up with frozen water particulates commonly called "ice". The ice was formed because the pilots didn't go far enough left right up down backwards forwards sideways to avoid the storm. The pilots didn't avoid the storm because the captain failed to take the crossing of the ICZ seriously and instead went to sleep in his bunk with a woman. The captain didn't take the crossing of the ITZ seriously because he was complacent due to his vast experience. The captain achieved this vast experience by flying the plane too much. The captain flew the plane too much because Air France allowed the plane to take off from the ground. Air France allowed the plane to take off from the ground because the passengers payed them money. THEREFORE The passengers are to blame for the crash of AF447 and the proper judicial verdict is one of mass suicide by airliner.
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Bear, that is brilliant.
I agree...apart from the last bit. |
AF 447 crashed because the pilots allowed it to stall. The pilots allowed it to stall because they pulled back on the stick. They pulled back on the stick because they were confused. They were confused because the automation left them in the lurch. The automation left them in the lurch because of a mechanical problem with the speeder tuber thingies. The rest of your post is utter tripe. An ill-disciplined, poorly trained crew killed themselves and everyone on board through their own inadequacy. |
Bear
"The captain ... went to sleep in his bunk with a woman".
It's outrageous that you say such a terrible thing. Do you have any proof that he slept? |
@BEagle:
I don't think MountainBear was being entirely serious. :} |
Oldchina
I read somewhere they were all knackered because of too much bonking in Rio.
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Pulling back on the side stick sounds totally correct to me. Without stall protection any aircraft will stall with the stick way back. The reason for the loss of control is obvious. Why these two couldn't fly an airliner with one failure, AS, which caused the AP to disconnect is beyond me. Experience level is still my guess. Monitoring an autopilot again does not count for quality experience.
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I still don't have an answer to this question - if they are in this very low forward-air-speed, very high nose-up situation, is it easy with the right inputs to bring the nose down in time? How long does it take? That seems very important. You are falling, and the solution is to hold the stick/yoke forward and trim the stabilizer to help and reduce thrust, even if it takes 30 seconds to get a result. That would require a lot of discipline. To do that, you'd have to be damn sure that it was going to work. So would it?
Another thought is - have we found the Achilles heel of the modern wing? The unspoken factor in this crash is the wing design. Does it have this ability to fall like a leaf in honey because otherwise it is so very efficient? |
Originally Posted by deSitter
(Post 7297619)
I still don't have an answer to this question - if they are in this very low forward-air-speed, very high nose-up situation, is it easy with the right inputs to bring the nose down in time? How long does it take?
The first experiment involved setting the conditions to night IMC with CBs in the vicinity, having set the autoflight to take us to 35,000ft and hold us there. We had a friend of his who is a TRE sitting in the LHS to provide guidance and monitor what we were doing. He then failed the ADCs, leading to autopilot disconnect and a drop to Alternate (without speed stability) and we tried to follow through and maintain a 15 degree pitch angle. Things we noted: I'd suspected it would involve considerable effort to hold the sidestick there for a significant amount of time, but I was genuinely surprised at just how much. The zoom climb occurred exactly the way we expected The Alternate Law (no speed stability) on the A320 seems to have a hard trim limit of 3 degrees nose up It was definitely possible to hold the aircraft in the stall with 3 degrees of nose-up trim and full back stick, but it required effort The aircraft wanted to nose down and recover itself, and with about 10 degrees of nose-down maintained with the sidestick at the moment we passed about 30,000ft, we managed to effect a recovery with the speed coming back up to a point where we could level out safely at about 20-25,000ft judging by the standby altimeter. The second experiment was the same as the first, but as my pal had noted, the A320 has a hard limit of 3 degrees NU trim available via autotrim in the secondary Alternate Law. We tried again, this time winding in full nose-up trim manually just prior to the point of stall. This time: The aircraft seemed more willing to hold pitch with the trim at full-up, but to hold it at 15 degrees still required considerable effort We had to add a touch of rudder (on the TRE's advice) to control the roll. Despite full nose-up trim, we elected to start a recovery as we came down through about 35,000ft this time, just to see if it was possible using sidestick only Following the same 10 degree nose-down sidestick demand as before, the trim rolled forward with the sidestick demand, returning to around neutral within about 5-8 seconds, and we came out of the stall as before. Based on this, as far as the A320 is concerned at least, recovery is possible using autotrim via sidestick only even when the trim has been manually wound fully nose-up. Given more time we'd have liked to see what happened attempting recovery at lower altitudes, but the general take-away seems to be that with sufficient forward sidestick demand it is possible to recover from stall even with trim forced to where it's not supposed to be. |
Hi,
DeSitter How long does it take? That seems very important. You are falling, and the solution is to hold the stick/yoke forward and trim the stabilizer to help and reduce thrust, even if it takes 30 seconds to get a result. That would require a lot of discipline. To do that, you'd have to be damn sure that it was going to work. So would it? That's keep pulling on the stick will not help for recovery So why not take the chance to push on the stick .. and pray .. At least .. better try to recover instead the contrary .. ! |
DozyW your answer to deSitter
@ DozyW concerning your experiment in an A320
It´s about time to rethink the value of the your tests and the result it presented. If it would have been that simple then BEA would have adopted that kind of cheap and easy testflight and would have presented the results out of it. But as we can see in the following excerpts from the final report BEA has completely missed that possibility (which i doubt) or BEA came to the result, that such a test would be far off from reality. They even could have used an A330 simulator instead an A320 like you did, but again, they didn´t. So we should accept your A320 test as an experiment with some discussion value in the period before the final report came out, but without reference or firm basis for answering questions, even BEA didn´t dare to. Let´s focus instead on the report, there is enough potential for discussion and rethinking of former own positions and asumptions in it. BEA FR 1.16.4.1 The validity of the model is limited to the known flight envelope based on flight tests. Consequently, it was possible to conduct the simulation on the period from 2 h 10 min 00 s to 2 h 10 min 54 s. BEA FR 1.18.4.2 ˆValidation (proof-of-match) tests compare the behaviour of the simulator with that of the aircraft. A set of technical data (the data package) compiled during flight tests and aircraft certification serve as reference data for this objective comparison. The data only covers the aircraft’s known flight envelope; In a developed stall situation the aircraft has left its known flight envelope. The data package does not contain any data relevant to this situation. The simulator is not representative of the aircraft in a developed stall situation; it does not reproduce the deterrent buffet effect. 1.18.4.5 Information reported by the manufacturer and the operator: The information provided by Airbus and Air France managers highlighted the following: ˆˆThe data currently available in the data packages prevents the simulator’s flight envelope from being extended, since the data in this package is limited to the aircraft’s known flight envelope; ˆˆSimulators do not indicate to the pilots and instructors that the simulator has been taken outside the envelope validated by the data packages. Improvements to this situation would appear, however, to be possible; 1.18.4.6 Work currently underway on simulator fidelity and training: Following the accident to the DHC-8-400 operated by Colgan Air(17) on 12 February 2009, one of the NTSB’s recommendations (A-10-24) was that operators (notably of public transport aircraft) should define and codify minimum simulator model fidelity requirements to support the training of pilots in how to recover from stalls, including stalls that are fully developed. These simulator fidelity requirements should address areas such as angle of attack and sideslip, motion cueing, proof-of-match with post-stall flight test data, and warnings to indicate when the simulator flight envelope has been exceeded. ˆSimulator fidelity must be improved to avoid the risks of negative training; 2.1.3.5 End of the flight: At about 2 h 12, descending though FL 315, the aeroplane’s angle of attack was established around an average value of about 40 degrees. Only an extremely purposeful crew with a good comprehension of the situation could have carried out a manoeuvre that would have made it possible to perhaps recover control of the aeroplane. In fact, the crew had almost completely lost control of the situation. BEA 2.2.5 However, positive longitudinal static stability on an aeroplane can be useful since it allows the pilot to have a sensory return (via the position of the stick) on the situation of his aeroplane in terms of speed in relation to its point of equilibrium (trim) at constant thrust. Specifically, the approach to stall on a classic aeroplane is always associated with a more or less pronounced nose-up input. This is not the case on the A330 in alternate law. The specific consequence is that in this control law the aeroplane, placed in a configuration where the thrust is not sufficient to maintain speed on the flight path, would end up by stalling without any inputs on the sidestick. €EASA modify the basis of the regulations in order to ensure better fidelity for simulators in reproducing realistic scenarios of abnormal situations; [Recommendation FRAN‑2012‑045] |
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I basically agree with your post concerning SIM discussion concerning AF447 recovery from stall or not. If you refer to my post #219 in the Tech Log, it explains, IMO, why the BEA didn't get into the whether or not recovery was possible. It isn't in their charter to figure that out, as factually, no recognition of a stall was made by the crew of AF447.
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TurbineD
Howdy. Can you clarify? Are you saying that the actual STALL was left off because the pilots hadn't acknowledged it? Seems like odd criteria to drive an investigation. A major disappointment has been the lack of attention given to this area by the BEA. We are left to wonder about this. My problem with BEA in this area has to do with their lack of substantiation that the STALL WARN was not heard, ignored, or actively disregarded by crew. Thus far, we are missing the statement: "throughout the recorded conversations and CAM, there was no hint nor evidence that the Stall Warning was acknowledged in any way." Is there? Because when redacting or witholding, some purpose and conclusion needs to be stated, lest the public be left wondering. I wonder about the CVR, of course. It is a mystery. |
Lyman:
Between this thread and a number of AF 447 threads in Tech Log, there have been posts by credible contributors that indicate that a good estimate <---- of the time it takes to unstall that aircraft (depending on when recovery was begun and how stalled it was) lies somewhere between 10,000 to 15,000 feet. Maybe. Part of that estimation seems to be based upon "if you hold it in for X long" it takes you longer to recover than if you begin recovery right after stall onset. What the collective judgment seems to be is that the longer one holds it in (as the crew did) the higher the AoA will become (up to a limiting value?) hence the longer to recover (time it takes to change AoA to "flying" rather than "stalled") IF AND ONLY IF the crew discerns that "we are stalled, time to commence recovery" AND the crew begin to lower the nose, lower the AoA, and adjust power (???) as appropriate. BEA seems to me to be in a "damned of you do and damned if you don't" position if they open that can of worms. The DATA they are working from never shows stall recognition. Therefore, BEA can't guess how high the AoA MIGHT have been when initiation of recovery was commenced, and they thus cannot speculate on how possible it was to recover. To toss out a few examples: Were stall recognition made at 36,000 feet (fairly early into the stall), you'd have one estimate of how long to recover if X nose down was done. If "we are stalled" recognition is made at 30,000, another estimate If "we are stalled" recognition is made at 25,000, another. And so on. There is also, due to lack of a standard trained response for stall recovery (fleet wide?), unanswerable recovery methods such as -how much nose down -what power -configuration which can only be derived in hindsight regarding the following: "Well, how much nose down can you expect the crew to use to unstall?" All BEA might be able to speculate about is where the point of no return might have been. They have insufficient data (IMO, to include training and wetware issues) to work with to allow them to approach an analytical statement like the following strawman: "Had they acknowledged stall at 13,500 feet (or some such number) or less, it would not have mattered, since it takes more than that to unstall from X AoA. Had they arrived at the conclusion that "we are stalled" at 14,000 feet, we believe for reasons x, y, and z that the crew would have had a good chance at recovery ... " NOTE: Numbers for illustrative purposes ONLY. (This for the journos and gadflies who read here ...) I will repeat, due to my belief on how important this is, that since the initial condition for recovery "Mon dieu, those crickets were telling the truth, we are stalled!" was NEVER encountered, the BEA cannot make a valid finding, and can do speculation rather than analysis. What they can ask the industry to do is figure it out, which the industry might not do. Getting those kinds of test points isn't just expensive, it can be dangerous to the flight crew, and may or may not be worth the money invested. Based on what a number of sober and credible professional airline pilots and engineers (I do not include myself in that company) have contributed in these discussions, I suggest to you that chasing that set of data points has less expensive, less risky, and more pilot friendly alternatives. I believe the BEA came to a similar conclusion. |
@franzl (RF4) and TD:
The test was primarily to determine *systems* behaviour, and does not attempt to answer questions outside of that scope. The question was whether forward stick would be enough to either overcome or counteract the THS position in the time available, for which the answer was affirmative. In addition, the recovery procedures we attempted were performed in the early phases of the stall - right after to the point where the THS rolled back. We did not hold the stall to the point where the sim behaviour would deviate significantly from the real thing due to the data from the real aircraft never having been gathered in those conditions. TD - you're absolutely right about the BEA's remit, and that extends also to other factors that some on here complained about (e.g. pinger behaviour and search/recovery post-mortem). The BEA is an aircraft accident investigation bureau, they are not specialists in deep-ocean recovery, nor was stall recovery assessment part of their duties in this case. That getting the nose down, building up speed and returning the wings to flight is the proper stall recovery procedure should be a given. I would only expect them to comment on that aspect if any systems or airframe anomalies had presented themselves during the course of the investigation.
Originally Posted by Lyman
(Post 7298464)
My problem with BEA in this area has to do with their lack of substantiation that the STALL WARN was not heard, ignored, or actively disregarded by crew.
Because when redacting or witholding, some purpose and conclusion needs to be stated, lest the public be left wondering. I wonder about the CVR, of course. It is a mystery. If you're trying to infer that they have redacted pertinent content for nefarious purposes, don't be shy - come out, say it and explain your reasoning. |
Scott gets a wild hair
There are probably any number of objections to this idea, not least, it would be very expen$ive. What about this?
Procure an old 332. Fit it with robo-remote-controls (pilotless). Fit it with advanced recording/telemetry equipment. Fly the thing out over an ocean, and stall the thing. That airliners are not tested for actual stall characteristics is emerging as unacceptable, IMHO. Discuss. (Runs, hides.) |
That's an excellent idea in fact.
Let's assume the worst and it's not possible to recover wings-level from 40 nose up at 60-100 air speed and dropping fast at 25k. Can you apply differential thrust and roll out of it? Wouldn't that in fact bring the nose down by itself? If this airplane is discovered to have a stall regime in which recovery is difficult or impossible even from a substantial altitude, would that be enough to cause some airworthiness action? |
Pilotless Stall Test
Thanks, deSitter,
I think the tentative answer to your first assumption has been, yes, probably, maybe, but not verifiable, it might have been recoverable by standard nose-down/throttle adjustments (see Thread #9) and your second question has already been answered a few times in this thread, as (paraphrased), 'not necessary.' |
The BEA is an aircraft accident investigation bureau, they are not specialists in deep-ocean recovery, Why mandate the BEA ? and over all why let him organize and coordinate (the BEA have the last word but are.. from your own words .. no specialist of deep - ocean recovery) Page 85-86 final report 1.16.1 Underwater search and recovery operations The BEA was mandated after the end of the search and rescue operations (SAR) with the organisation and coordination of operations carried out by France for the search and recovery of the wreckage. Given the distance from the accident and the topography of the sea bed, this particular mission required the considerable mobilisation of air, naval and underwater forces and, even more so, of multidisciplinary skills (safety investigators, scientists, the army, underwater search experts, etc). The wreckage of the Rio-Paris flight aeroplane was found on 2 April 2011, 22 months after disappearing. A special document on the four sea search phases and on the recovery phase will be the subject of a separated publication. The lack of success during the first three search phases led the BEA to undertake a complete review of both the means used and the zones explored. Drawing on all the elements provided by various partners in the searches (scientific institutes, statistical analysts, oceanographers, etc), and comparing them with the result of the previous phases, the BEA decided to redirect its search strategy by leading a final systematic search operation in all the areas not explored during phases 2 and phase 3, beginning within a circle of 20 NM from the last known position. The Phase 4 operations took place from 25 March to 9 April 2011. The REMUS 6000 AUVs were used again in the search during this phase. They were operated by WHOI from the Alucia, property of Deep Ocean Expeditions. Discovery of the accident site On 2 April 2011, the data from the 18th AUV mission was recovered, and analysis of the sonar images brought to light a concentration of backscattered parts on the sea bed distributed over a rectangular area of about 600 by 200 metres. A mission to identify the type of components by photographs was immediately scheduled. This mission ended on 3 April 2011 and the photos taken confirmed that |
@ Lyman,
Lyman Quote: Howdy. Can you clarify? Are you saying that the actual STALL was left off because the pilots hadn't acknowledged it? Seems like odd criteria to drive an investigation. A major disappointment has been the lack of attention given to this area by the BEA. We are left to wonder about this. The point is, had the AF447 crew recognized and attempted to recover from the stall they were in, but failed, then the BEA may have been obligated to examine if the aircraft was recoverable or not and provided an answer the question. If this were the case, SIM experiments and characterization of the event at the stall point would have to be developed for the SIM and testing accomplished. But I believe the outcome and conclusion would have been hedged absent actual aircraft testing. Lyman Quote: Thus far, we are missing the statement: "throughout the recorded conversations and CAM, there was no hint nor evidence that the Stall Warning was acknowledged in any way." Is there? Because when redacting or witholding, some purpose and conclusion needs to be stated, lest the public be left wondering. - - The crew not identifying the approach to stall, the lack of immediate on its part and exit from the flight envelope, - The crew's failure to dianose of the stall situation and, consequently, the lack of any action that would have made recovery possible. Page 198 - CONCLUSION - 3.1 - Findings - Neither of the pilots made any reference to the stall warning or to buffet. - Neither pilots formally identified the stall situation. |
@jcj:
I'm sure they delegated the actual technical co-ordination of the search to the team contracted to do the work. The BEA's brief probably only extended to "we need to find this wreckage - here's where we think it is". |
"we need to find this wreckage - here's where we think it is" When you are "mandated" for "organize" and "coordinate" .. this mean you bear all the responsibilities .. you are the chief of operations Who mandated the BEA .. when know that they are not specialists in researshes .. ? |
@jcj:
I suggest you do a little background reading into just how difficult deep-ocean search and salvage operations actually are before passing judgement on the BEA. |
I suggest you do a little background reading into just how difficult deep-ocean search and salvage operations actually are before passing judgement on the BEA. That was a big failure cause not use appropriate material (as used in phase 4) Who take the decision for not use additional material in phase 1 (more than just pingers detection ... as they know the area was flat so easy to be scrutinized wit material as used in phase 4) The phase 1 was triggered (location) cause ACARS (who indicated a stall) Why phase 2 was not a remake of phase 1 with appropriate material ? |
Such issues are mentioned in the report, as well as an admission that they'd learn from their mistakes and do better next time.
Is there a point to this line of discussion? |
I do not know who mandated the search be controlled by BEA, the Court?
Right wrong or indifferent, my guess is someone wanted the custody of the evidence to be tightly controlled, and protected. Something from ACARS motivated the quick retrieval of the avionics bay, and the seats, again, who knows why.... RetiredF4. Hi Franzl. For what it's worth, I would not fall over in a faint if it was demonstrated that parts of the report are "managed". If it is accurate, and I believe it to be so at some future time, I would consider booking a flight on Air France. Til then? Not so much.... |
Originally Posted by Lyman
(Post 7298979)
Something from ACARS motivated the quick retrieval of the avionics bay, and the seats, again, who knows why....
What's convinced you that they're hiding something - and why? There's no motive for doing so. |
Dozy, my brother and I talked about this mishap again last week.
Based on my recommendation to him well over a year ago, Air France is not on his approved travel list. I was modestly gratified to find out that he had discussed this with his manager, who after listening to the argument (informed somewhat by my inputs) agrees with his 'block' order for international travel fare comparisons before choosing a carrier. Thankfully, there are other airlines who service the same South American cities (to include Rio). |
Why they searched for AF447
They could have stopped looking for the plane, filed it all under "unproven cause" and let the insurers pay out.
The reason why such a huge amount of effort was expended to find the plane was that 50 million french people including politicians and company CEOs fly in those aircraft, and are piloted by guys trained in those procedures, and that it was really felt by everyone involved that an answer however unpleasant was better than no answer. And in fact there is one thing gained from the report. The certainty that in addition to some updates to airspeed measurement instruments, it will be necessary to update pilot training so that civilian pilots have at least minimal flying skills. The debate about confusing computer messages, sidesticks etc will probably take a few more accidents to progress usefully, I fear. |
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