Interesting note about AA Airbus crash in NYC
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I just hate the fact that I think the pilot was unfairly blamed.
Again, he wasn’t.
No; there is enough blame available to satisfy almost any one’s prurient interests.
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Got a page number handy? Must have missed that nugget...
Interesting if so, but I still don't think you can blame them entirely - because no matter the system used and no matter how sensitive it is, you don't apply opposite rudder to aileron in a sideslip and then reverse it multiple times.
The reason it seems a lot like blame is because it IS blame. It’s just not unfair blame. But, having said that, there certainly isn’t a shortage of blame to go around on this one. Inadequate information available on the airplane; at least as far as the kinds of controller deflection amounts and forces yielding the kinds of control surface deflections achieved. Inadequate regulations; or, at least inadequate understanding of what the regulations say. Inadequate understanding of the aerodynamics involved; at least as far as what was known, what was thought to be known, what was not considered about the rules, and how those rules play out in an airplane. Inadequate training; at least as far as correctly stressing when, if, and how the rudder should be used in recovering from inadvertent upsets. Inadequate follow-up; at least as far as one pilot’s opinion is concerned.
No; there is enough blame available to satisfy almost any one’s prurient interests.
No; there is enough blame available to satisfy almost any one’s prurient interests.
Effectively these Aircraft are continuing to operate under a de facto MEL, fit to continue flying as long as control inputs are manually limited.
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[UPDATE] Had a nosey. Hmm, been a while since I read this - interesting to note that Douglas's DC-9 and all later derivatives (including 717) also use a variable stop system. Airbus's later aircraft continued to use a variable stop system, albeit slightly less sensitive, so the they did not 'revert' to a Boeing-style variable ratio system after the A300-600/A310. According to the report, the change from a variable ratio to a variable stop system was because of fewer moving parts (therefore reducing failure rate) and projected failure modes being less potentially catastrophic.
Not something that could happen on, for example a B744 - with 80 lbs force needed to get to the stops.
The point is that an A300 will behave differently to a B744, as it has every right to and it is the pilot's job, and the job of those that train the pilot to take those differences into account and make them clear respectively.
I'm in agreement with the spirit of airsupport's statement:
Last edited by DozyWannabe; 27th Jan 2007 at 13:01.
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DozyWannabe -
I believe the change was also done due to weight and cost issues. IMO the 'better' system was overruled by economics.
All airliners can rip their tails off. The senisitivity of the A300-600 vs. other airliners is what the union had problems with. The reports I read stated the new design wasn't flight tested on the A300-600. Instead the A310 flight test data was extrapolated for the longer fuselage length of the A300-600. So they end up with the most sensitive rudder(rudder displacement per degree of rudder pedal travel) and it wasn't flight tested???
The early A300 models did not have the same rudder limiter. When the A300-600 was designed the rudder limiter was changed to the A310 design. A300-600 pilots actually get an A310 type rating.
Should Boeing be the standard? IMO it's approach(variable ratio) for rudder limiting should be the standard. I've flown both and IMO it's more consistent with what a line pilot would expect vs. the changing sensitivity of a variable stop type design.
I believe the change was also done due to weight and cost issues. IMO the 'better' system was overruled by economics.
All airliners can rip their tails off. The senisitivity of the A300-600 vs. other airliners is what the union had problems with. The reports I read stated the new design wasn't flight tested on the A300-600. Instead the A310 flight test data was extrapolated for the longer fuselage length of the A300-600. So they end up with the most sensitive rudder(rudder displacement per degree of rudder pedal travel) and it wasn't flight tested???
The early A300 models did not have the same rudder limiter. When the A300-600 was designed the rudder limiter was changed to the A310 design. A300-600 pilots actually get an A310 type rating.
Should Boeing be the standard? IMO it's approach(variable ratio) for rudder limiting should be the standard. I've flown both and IMO it's more consistent with what a line pilot would expect vs. the changing sensitivity of a variable stop type design.
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misd-agin
"..........The reports I read stated the new design wasn't flight tested on the A300-600. Instead the A310 flight test data was extrapolated for the longer fuselage length of the A300-600. So they end up with the most sensitive rudder(rudder displacement per degree of rudder pedal travel) and it wasn't flight tested???..............."
FYI:
The A321 was not initially flight tested in actual icing conditions. The A320 flight test data was extrapolated despite the different flap/slat design of the A321. It was subsequently tested and modifications were made to the ELAC system on or about the year 2001.
Caveat emptor.
"..........The reports I read stated the new design wasn't flight tested on the A300-600. Instead the A310 flight test data was extrapolated for the longer fuselage length of the A300-600. So they end up with the most sensitive rudder(rudder displacement per degree of rudder pedal travel) and it wasn't flight tested???..............."
FYI:
The A321 was not initially flight tested in actual icing conditions. The A320 flight test data was extrapolated despite the different flap/slat design of the A321. It was subsequently tested and modifications were made to the ELAC system on or about the year 2001.
Caveat emptor.
Last edited by Tree; 28th Jan 2007 at 00:37.
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FYI:
The A321 was not initially flight tested in actual icing conditions. The A320 flight test data was extrapolated despite the different flap/slat design of the A321. It was subsequently tested and modifications were made to the ELAC system on or about the year 2001.
Caveat emptor.
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Companies design derivatives, rather than all-new designs, partly to save on development costs, and the use of "similarity" and analysis in lieu of test is common.
Any model that isn't the original of the type will have any number of "extrapolations" - all of which form part of the certification of the type.
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The ideal would be a system which restricted the travel of the pedals as it restricted the travel of the rudder (which is basically the variable stop design) while also causing the force level to achieve the maximum travel to be broadly consistent (which is what the variable ratio does). Unfortunately, trying to meld both systems would undoubtedly yield a rather complex and unreliable design.
Omitting either part of the "ideal" gives a potential for poor feedback, and possible handling issues; I'm not sure the balance of advantage lies with either approach.
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Misd-again: Regardless of the cost angle, Airbus do have a point about fewer moving parts meaning lower failure rate though, and that's an engineering fact - the biggest example in aviation being the move from piston to jet engines.
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I don't know why Airbus changed the design. We have cost(proven), weight(proven), and better failure mode(hypothetical?). I'd vote for lower cost, weight, and ease of manufacture as the reasons behind the change.
It's obvious from the accident investigation that even the Airbus pilots had handling issues in the simulator if they pushed the rudder pedal .6 of an inch. Full scale deflection, and the potential for the unwary to start a PIO due to 'startle effect', occurred. To me that's a poor design.
The 737 rudder failures are related to hydraulic actuator issues that all a/c have.
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How many rudder control failures have you heard about, from either system, that are related to the design of the rudder limiter? I can't recall any, which to me indicates that there's no empirical safety benefit from having fewer parts.
I don't know why Airbus changed the design. We have cost(proven), weight(proven), and better failure mode(hypothetical?). I'd vote for lower cost, weight, and ease of manufacture as the reasons behind the change.
I don't know why Airbus changed the design. We have cost(proven), weight(proven), and better failure mode(hypothetical?). I'd vote for lower cost, weight, and ease of manufacture as the reasons behind the change.
The fact remains that a variable stop system was used by Douglas as well as Airbus in aircraft that have been considered safe for decades, so any talk of deficiency in design is disingenuous to say the least.
The system on the A300 is sensitive, and as such not ideal - but then the variable-ratio lever system requires more frequent safety checks and is a less elegant design and therefore not ideal either. It's swings and roundabouts as to which is chosen and it's unfair to say that one system is superior to the other in all aspects.
As for the 737 rudder issue, Boeing's contractor Parker Hannifin developed a single-valve design to keep weight and costs down. It was an elegant design, however the engineering cost was a loss of redundancy compared to dual-valve designs. As such it was a problem specific to that model and that manufacturer.
I know that no matter how hard we try, we will always have a bit of national pride in our manufacturers and it's hard to avoid that flaring when we feel that they are slighted. In this case there is nothing inherently wrong with the A306/310 system as long as conversion training takes into account that the pedals are more sensitive than the pilot may be used to on other types.
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Hundreds, if not thousands.
Companies design derivatives, rather than all-new designs, partly to save on development costs, and the use of "similarity" and analysis in lieu of test is common.
Any model that isn't the original of the type will have any number of "extrapolations" - all of which form part of the certification of the type.
Companies design derivatives, rather than all-new designs, partly to save on development costs, and the use of "similarity" and analysis in lieu of test is common.
Any model that isn't the original of the type will have any number of "extrapolations" - all of which form part of the certification of the type.
I have been aware of that for a very long time but I am surprised at the depth of the process with some manufacturers.
From a flight safety perspective I believe that information should be readily available to the pilot on the transition course and in the AFM (i.e. this aircraft has not been flight tested in ........conditions); otherwise we are unknowingly operating in a manner similar to a -x registration.
Last edited by Tree; 28th Jan 2007 at 17:03.
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I just hate the fact that I think the pilot was unfairly blamed.
Again, he wasn’t.
Originally osted by theamrad
Well….To quote the Probably Cause from the NTSB report:
……created by the first officer’s unnecessary and excessive rudder pedal inputs.”
Seems a lot like blame to me.
Well….To quote the Probably Cause from the NTSB report:
……created by the first officer’s unnecessary and excessive rudder pedal inputs.”
Seems a lot like blame to me.
The reason it seems a lot like blame is because it IS blame. It’s just not unfair blame. But, having said that, there certainly isn’t a shortage of blame to go around on this one. Inadequate information available on the airplane; at least as far as the kinds of controller deflection amounts and forces yielding the kinds of control surface deflections achieved. Inadequate regulations; or, at least inadequate understanding of what the regulations say. Inadequate understanding of the aerodynamics involved; at least as far as what was known, what was thought to be known, what was not considered about the rules, and how those rules play out in an airplane. Inadequate training; at least as far as correctly stressing when, if, and how the rudder should be used in recovering from inadvertent upsets. Inadequate follow-up; at least as far as one pilot’s opinion is concerned.
No; there is enough blame available to satisfy almost any one’s prurient interests.
No; there is enough blame available to satisfy almost any one’s prurient interests.
I said that if one was looking to assign “blame” there is a lot that could be assigned. I said that because I believe it to be true – for all the reasons I indicated in my earlier post.
I understand that you believe the negative comments made by a former colleague are not any more conclusive than the positive comments made by other former colleagues. Fair enough. But I believe that any such negative comments would have to be prompted by a control input response worthy of such comment. I also believe that this pilot was only prompted to apply control inputs this way under very limited circumstances. If what I believe is actually correct, this pilot would not have been seen exhibiting such negative tendencies during otherwise “normal” flight conditions.
I also understand that you (and perhaps airsupport) believe that the vertical stabilizer on that aircraft had (and perhaps you believe it still has) a problem. IF that is true, I don’t see anything in this particular accident that would confirm such a suspicion. The vertical stabilizer separation on the accident aircraft appears to have occurred at the point where multiple maximum rudder deflections would have resulted in failure of the component. FDR data recordings indicate that control inputs were not made in response to aircraft uncommanded movement. Instead, it appears that aircraft movement was precisely and accurately a result of commanded controller input – in all three axes.
You said that you believe the issue of whether or not the PF was or was not exercising “poor or otherwise” airmanship was inconclusive – and, that the official report “moots” that specific point. I disagree. I read the report as stating what it states – that there were multiple, maximum, continually reversed control inputs, ultimately leading to structural failure of the vertical stabilizer. I think you have every right to disagree with the official findings. However, to say that the official findings make “moot” (or relegates the finding to be questionable or irrelevant) the particular point of over controlling and reversing the inputs is … well … simply not accurate. The official report does not dismiss the over control – it, in fact, cites that as cause.
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Hey! Lighten up just a bit, there theamrad! I did not say “the accident is everyone’s fault.” And, I am at a loss to understand why you think my opinion is any less valuable than your opinion or that any comments I’ve made are any less rational than anyone else’s here. I certainly did not insult you (or anyone else) personally OR professionally … at least not that I am aware of and certainly not intended if you or anyone else took my comments that way. I certainly didn’t accuse you of posting “juvenile badinage.”
crosswinds? a little drift doesn't hurt anyone
just thinking aloud...not responding
it's not uncommon for operating limitations of such heavy consequence to be placcarded, is it?
some planes pulling this stick up will start a climb and maintain airspeed and thrust setting... very expensive complex planes that have very specific control systems and requirements so it's not such a generic consideration as can be applied to a small trainer. so I'm in full agreement with the poster Jondc9
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Ok then, AirRabbit, to go back to my use of the word moot - I think you misunderstood me - I'm not saying the report is relegating that point. I'm saying that there is enough information within the report itself to call into question some of the assertions which may be made. Specifically, the FDR acquisition rate and the boards own acknowledgment that the vertical simulator(due to it's own limitations) could not replicate the full range of motion of the accident airplane. This, in my opinion, places at least some doubt on the accelerations and therefore pilot perception of accelerations felt during those simulator tests.
There's nothing in what I've said that would impune that statement. But we already know from the board's own tests (actually airbus's ground testing) that "test subjects" had difficulty making less than full rudder deflections when asked to do so. And also, IMO crucially, that "most" of the boards own "testees" used some rudder with aileron as their own preferred method of recovery in simulator tests. This particular point was also made during the public hearings, and not only by AA pilot sources. I think that should have been foremost in the thinking of the board when drawing their conclusions. I don't believe there was inadequate follow-up in the course of the investigation, personally I can't see a problem there. But what I'm baffled about, are some of the conclusions drawn by the board, and the order in which they were presented in the way of cause.
The only further thing I can add is my opinion of what might have happened. Whether or not there was some adverse yaw due to wake turbulence is a matter which I or (I believe) the board cannot ascertain with absolute certainty. While many may say the use of rudder in nothing more than a wake turbulence encounter is wrong - it is a fact, established during simulator testing the most of the test subjects DID use rudder when recovering from and UPSET. I can only say that it's possible, through the slow FDR aquisition rate, that PF perceived a roll or yaw rate which was not picked up by the FDR, and which he thought warranted use of rudder as well as aileron. Whether right or wrong (and I think PROBABLY wrong) he got a whole lot more than he intended, thanks to the oversensitivity of the rudder, and ended up with a (severe) apc event. I can't say anymore about the failure to recognise this situation and unload the controls - but then that's a matter that's been discussed many times in other places.
DozyWannabe;
I'm not actually trying to suggest that in a general way. I'll go as far as to suggest it for rudder control - but then I don't see it as a 'Boeing way of doing things' only - since airbus did use it. I'm not trying to go down the road of a B vs. A discussion here, since I acknowledge the opinions of those who have experience on both and say there are specific things that one does better than the other and vica versa. In using the B744 as an example, that's all it is, nothing more, and because it's where my personal experience/knowledge is best. After all, I'm mindful of Boeing's approach to the Colorado Springs accident investigation all those years ago - something which upset more than a few people in the NTSB.
In terms of flight certification, I wonder what gereral line pilot opinion is on the matter with regard to APC susceptiblility. Does anyone else find the approach to it a bit on the subjective side?(potentially at least).
Since this is left completely to the opinion of the test pilot and what he thinks is acceptable/difficult for OTHER 'average' skilled pilots who don't have the same experience base as a test pilot.
While grandfathering of certification is something that makes a lot of people feel uneasy - without it there would be lot less done in the way new aircraft or variations on existing types due to the cost and time needed for full certification. While I think there's some room for tightening up the circumstances in how and when it's allowed - I think it will continue to be the reality for design for a long time to come, and necessarily so.
The vertical stabilizer separation on the accident aircraft appears to have occurred at the point where multiple maximum rudder deflections would have resulted in failure of the component
The only further thing I can add is my opinion of what might have happened. Whether or not there was some adverse yaw due to wake turbulence is a matter which I or (I believe) the board cannot ascertain with absolute certainty. While many may say the use of rudder in nothing more than a wake turbulence encounter is wrong - it is a fact, established during simulator testing the most of the test subjects DID use rudder when recovering from and UPSET. I can only say that it's possible, through the slow FDR aquisition rate, that PF perceived a roll or yaw rate which was not picked up by the FDR, and which he thought warranted use of rudder as well as aileron. Whether right or wrong (and I think PROBABLY wrong) he got a whole lot more than he intended, thanks to the oversensitivity of the rudder, and ended up with a (severe) apc event. I can't say anymore about the failure to recognise this situation and unload the controls - but then that's a matter that's been discussed many times in other places.
DozyWannabe;
One of the things that has concerned me is the way people see the Boeing way of doing things as a de facto standard that all manufacturers should follow if the manufacturer doesn't want to get blamed by pilots for behaving in a different way to a Boeing aircraft.
In terms of flight certification, I wonder what gereral line pilot opinion is on the matter with regard to APC susceptiblility. Does anyone else find the approach to it a bit on the subjective side?(potentially at least).
Since this is left completely to the opinion of the test pilot and what he thinks is acceptable/difficult for OTHER 'average' skilled pilots who don't have the same experience base as a test pilot.
While grandfathering of certification is something that makes a lot of people feel uneasy - without it there would be lot less done in the way new aircraft or variations on existing types due to the cost and time needed for full certification. While I think there's some room for tightening up the circumstances in how and when it's allowed - I think it will continue to be the reality for design for a long time to come, and necessarily so.
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Ok then, AirRabbit, to go back to my use of the word moot - I think you misunderstood me - I'm not saying the report is relegating that point. I'm saying that there is enough information within the report itself to call into question some of the assertions which may be made. Specifically, the FDR acquisition rate and the boards own acknowledgment that the vertical simulator(due to it's own limitations) could not replicate the full range of motion of the accident airplane. This, in my opinion, places at least some doubt on the accelerations and therefore pilot perception of accelerations felt during those simulator tests.
While I believe I understand your explanation about the use of the word “moot” when you described the PF “airmanship,” the determination as to whether or not the PF was exercising “good” or “not so good” airmanship comes down to whether or not we can determine what the PF did; and its almost irrelevant as to “why” he did what he did (and I DID say “almost”) – the only thing that counts is did he do it or not. I believe the FDR supplies abundant information in that regard. However, I believe you are saying that there may be additional information that is NOT available from the CVR and FDR, and that missing information may call into question the decision we make about the PF airmanship. I also believe you are saying this because of the Board’s report that says the following:
The VMS was not able to replicate the target longitudinal, lateral, and vertical accelerations for short periods of time during the accident sequence, and the entire sequence could not be replicated in a single series of motion because of limitations in the VMS motion system. Further, it is possible that small differences between the actual acceleration and the derived values (that is, the acceleration between data points) may exist because of the low sample rate of the pitch, roll, and heading data recorded on the FDR.
The first is about motion systems on flight simulators. Yes, the VMS set-up at NASA Ames is the world’s largest motion-based aircraft simulator – and it IS impressive; and, yes, I have flown it. However, all simulators with motion systems, even the Ames VMS, are able to only provide “on-set” cueing to the pilots. While it is true that the VMS is able to provide a somewhat longer “on-set” cue than a traditional airline simulator with which you are no doubt familiar – it’s not as much as you might think. Getting a sustained motion cue in a simulator would require at least something on the order of a centrifuge – but they have problems on the other end. It’s not very realistic to be “parked at the gate” and experience 1.3 g’s! The reason that motion-based simulators can only simulate “on-set” cues is that the acceleration (either linear or angular) must be dampened out and the system re-set to the neutral position to be ready for the next motion cue before the system reaches its maximum extension capabilities. This process must be done below the pilot’s threshold of recognition, or he will be “fooled” into thinking that the airplane is moving in the opposite direction. This is because the simulator IS, actually, slowing down first – and then it IS being moved in the opposite direction. However, if it is done correctly, the pilot will not be aware that this is happening. So, while the VMS is a monster of a machine – and it can move a substantial distance in communicating the “on-set” cue – it really has its work cut out because it has to reset whatever distance it has moved and it has to be done quickly, quietly, and below the pilot’s recognition threshold.
The second is about the additive, or complimentary, effect that a visual system has in relation to a motion system. Airline training simulators have rather sophisticated visual systems – most of which provide something like a horizontal field of view that is 150 degrees and many go up to 210 to 220 degrees, and a vertical field of view that is at least 40 degrees and many go up to over 60 degrees. When the motion system provides an “on-set” cue that the pilot “feels” in his butt, and what he sees in the visual system out in front and along side his aircraft confirms this motion on-set, it is the visual system that continues to reinforce the “motion” cue – even when the motion system movement is slowing down and re-setting to neutral.
The next, and also a very important, factor that you must understand about the use of the VMS simulator cab for these tests is found also in the text of the Accident report. It says the following:
Regarding the second notable event experienced in the cab (that is, the second encounter with wake turbulence), the participants generally agreed that “very slight” cab motions were felt before the first movements of the control wheel and rudder pedal to the right. The cab motions were described as “barely perceptible” left lateral accelerations. Most participants did not experience any cab motion until less than 1 second before the first wheel motion. The first movements of the control wheel and rudder pedal to the right were “large and abrupt.” The participants did not observe a visual or (detect an) acceleration cue that would cause a pilot to apply the observed initial magnitude of wheel and pedal in response to the second notable event. After the first movements of the wheel and pedal to the right, large lateral accelerations were felt, and additional large, abrupt flight control movements in the yaw, pitch, and roll axes were observed. Although the participants felt lateral accelerations, they indicated that it was difficult to sense whether vertical and longitudinal accelerations were also present.
This warrants a discussion about the “accuracy” of the data used in the simulation as compared against the data that was recorded on the FDR. I can, if you desire, provide you with information about the accuracy of the data with which simulators are programmed – but, I suspect you probably don’t need that reassurance. The data collected by the FDR is certainly not in the same “league” as far as the frequency of data samples taken for things like aircraft certification is concerned. The FDR on this accident airplane took data at either 1 or 2 hertz (Hz), that is once or twice a second, depending on the data. Cockpit controller deflection information, I understand, was retrofitted in accordance with a recent FAA regulation change to be collected at 1Hz, but the remaining information was collected at 2Hz. This particular rate of data sampling is not very fast when compared against data collection during aircraft certification, for instance, where data sampling rates can be seen anywhere from 50Hz to 200Hz. The higher the rate of data sample collection, the more accurate a mathematical model may be that represents that particular function. The more data points in a given time, the smoother the curve is the result.
However, having said this, it is important to note that the “accuracy” of any individual data point – regardless of the frequency with which the preceding or succeeding data points were collected – is not in question. In this particular case, the issue has to do with the movement of the airplane. It would have been nice to collect that data at 50Hz, fifty times a second. That would have allowed a relatively smooth curve to be drawn between two specific times on a graph. But the issue here is whether or not it is likely that the airplane may have moved (or been moved) and then returned (or been returned) to essentially the same state between data samples taken by the FDR. The NTSB report clearly states that the time between the two data points (either 1Hz or 2Hz) is not accounted for – but that is one or one-half of a second. We’re discussing a rather large airplane. Large in mass. Large in momentum. It would take a rather serious force to move that mass any distance in one-half, or one-quarter, of a second and then another sizable force, operating exactly opposite to the first one, in exactly the opposite direction, also in one-half or one-quarter of a second, to bring the aircraft back in line with the other data points that were continually being taken at once or twice a second; and the distance moved would have to be quite small. Not only is this highly unlikely, it borders on the impossible. That is the reason that the Board reached the conclusion that:
The cab motions were described as “barely perceptible” left lateral accelerations. Most participants did not experience any cab motion until less than 1 second before the first wheel motion. The first movements of the control wheel and rudder pedal to the right were “large and abrupt.” The participants did not observe a visual or (detect an) acceleration cue that would cause a pilot to apply the observed initial magnitude of wheel and pedal in response to the second notable event.
AND
The external moments and wind gusts fully accounted for the effect that the wake turbulence had on the airplane, as recorded by the FDR. Any additional effects of the wake turbulence that were not recorded on the FDR (because of limited sampling rates, for example) would have had a negligible impact on the airplane motion.
AND
The external moments and wind gusts fully accounted for the effect that the wake turbulence had on the airplane, as recorded by the FDR. Any additional effects of the wake turbulence that were not recorded on the FDR (because of limited sampling rates, for example) would have had a negligible impact on the airplane motion.
(W)e already know from the board's own tests (actually airbus's ground testing) that "test subjects" had difficulty making less than full rudder deflections when asked to do so. And also, IMO crucially, that "most" of the boards own "testees" used some rudder with aileron as their own preferred method of recovery in simulator tests. This particular point was also made during the public hearings, and not only by AA pilot sources. I think that should have been foremost in the thinking of the board when drawing their conclusions. I don't believe there was inadequate follow-up in the course of the investigation, personally I can't see a problem there. But what I'm baffled about, are some of the conclusions drawn by the board, and the order in which they were presented in the way of cause.
The second test using a simulator was a simple “Training Simulator Study.” Here there were 6 trials using the A300B4-600 flight simulator. In the first trial, the simulator was inhibited in its response (to allow the airplane to reach a substantial bank angle before recovery began). While in a 20-degree left bank, at an altitude between 2000 and 2500 feet, and an airspeed of approximately 240 knots, the computer input a roll in one direction (the direction was computer-determined in accordance with an arbitrary determination routine) followed immediately by a substantial roll in the opposite direction. The pilots were instructed to recover in accordance with the ground school training. This procedure was repeated 5 more times for each pilot, except that the roll maneuver was initiated during level flight after the pilot indicated he was “ready.” Each pilot was instructed to follow one of 5 specific recovery methods: 1) partial wheel and no rudder; 2) full wheel and no rudder; 3) full wheel and partial rudder; 4) full wheel and full rudder; and 5) the pilot’s preference. It would be a waste of time and space to reprint the complete results here (you can see them in the official report at section 1.17.1.2.6 Training Simulator Study), but each pilot reported the worst method was partial wheel and no rudder. The last trial (pilot’s preference for recovery method), most of the pilots responded with nearly full control wheel and partial rudder pedal inputs. Slightly less input was made on both controls than during the first trial, and the pedal response was typically delayed by at least 1 second after the control wheel response.
I would submit that the results of these simulator tests do little but confirm the rest of the Board’s report and are a far cry from what you believe the test results show.
The only further thing I can add is my opinion of what might have happened. Whether or not there was some adverse yaw due to wake turbulence is a matter which I or (I believe) the board cannot ascertain with absolute certainty. While many may say the use of rudder in nothing more than a wake turbulence encounter is wrong - it is a fact, established during simulator testing the most of the test subjects DID use rudder when recovering from and UPSET. I can only say that it's possible, through the slow FDR aquisition rate, that PF perceived a roll or yaw rate which was not picked up by the FDR, and which he thought warranted use of rudder as well as aileron. Whether right or wrong (and I think PROBABLY wrong) he got a whole lot more than he intended, thanks to the oversensitivity of the rudder, and ended up with a (severe) apc event. I can't say anymore about the failure to recognise this situation and unload the controls - but then that's a matter that's been discussed many times in other places.
The rate of FDR data acquisition is irrelevant unless you believe that the airplane could have been doing something really “screwy” between FDR captured data points and return to the same state every second or every one-half second.
Yes, most of the pilots in the simulator tests DID use some rudder in recovering from the upset to which they were subjected. However, the simulator was inhibited for a while to ensure a really significant bank angle was achieved. The report says beyond 100 degrees on average. None of the pilots used full rudder except when they were asked to – and none of the pilots reversed the control inputs.
Did the PF on the accident airplane get “more than he intended” thanks to the “overly sensitive rudder?” Perhaps. But why was he using rudder in the first place? He didn’t use rudder input during the wake encounter merely 12 seconds earlier. Why? The two encounters were very close, if not identical, in effect on the airplane.
Did the PF get into a Pilot Induced Oscillation (PIO)? Yes, I think he did and he didn’t know how to get out of it.
In my estimation, on the basis of logic, reasonable doubt, the diligent and careful manner in which this particular accident was investigated, and the voluminous amounts of raw and refined data, I think the Board’s report on this one is pretty accurate.