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In case of lost speeds, what value of speed is used by the FBW system to transfer a SS command to the appropriate elevator deflection? And does it change again when the speeds are valid again? Was the FBW system using low speed gains during the stall, high speed gains or preset gains (?) The report states that in ALT2B, pitch gains are fixed for 330 KIAS. Don't have the page ref at my fingertips, but it's in there and it's the only reference I've ever seen to this. From the simulations I've seen, it appears that the pitch gains are permanently fixed for 330 KIAS regardless of whether the speeds become valid again or not, this as a result of ALT 2B 'latching', and the fact that 'validity' is nothing more than two ADRs being within 25 KIAS. Though NO two ADRs within 25 KIAS starts a 10 second countdown for display of the ADR Disagree ECAM message....ALT2B with the associated fixed gains 'latches' within a couple of seconds. Once two ADRs are back within 25 KIAS (doesn't have to be the correct speed), the countdown is terminated and reset (and the FDs return, and no ECAM message if less than 10 seconds). But the gains remain fixed for 330 KIAS. There's a simple way to check this monitoring elevator deflection on the SD Flight Control page. I'm completely out of the business now, but with respect to all this discussion of simulator post stall behavior and subsequent recovery in a simulator, the last communication I read from a noted sim manufacturer stated that beyond a relatively early point in the sequence, as opposed to 'flying', one is simply operating a high dollar video game. |
RetiredF4
First I'm cautious concerning the extent of reality of present flight sims concerning stall behaviour and reaction of the sim on flight control inputs in this untested flight regime. The pitch response with manual trim is fairly gentle as one can only move the trim wheel about 90° at a time in the practical sense, before having to move your hand back and grip the trim wheel again (not like the Boeings with the fold out hand crank) Winnerhofer Disable AutoTrim in all Laws bar Normal as this is will force crew to be in the loop. A good example of this is a fault where autotrim fails, but manual trim is still functional. In this case the airplane appears to fly just fine, but the crew (directed by the non-normal procedure) must view the flight control page on the Systems Display-SD) and trim for neutral elevator. When this is happening, there is no feel change in the airplane, but as the stab position changes the elevator deflection necessary to maintain the commanded pitch response (i.e., 1g) changes accordingly. Obviously as the airplane slows for approach, the crew must continue this procedure, for if the didn't they run the risk of "running out of elevator" near landing as the elevator may (unbeknownst to the crew) be near full up just to maintain the approach trajectory (1g)and not have any excess for the flare. In alternate law, as the airplane approaches stall speed, the pitch law incorporates "stabilities",which when you get right down to it is changing to direct law in pitch and allowing the natural pitch stability of the airplane to become evident. The speed at which this occurs is not indicated. The trim stops—if it didn't then the stability would not be evident! The unfortunate part of this is (for AF447 type situations) is that indicated airspeed is required to make that change over (not just AOA). So, one must assume that in the case of invalid airspeed the SS remained a g/rate demand input. MrSnuggles I read some posts ago that maybe Bonin was afraid of an overspeed situation. While that is a serious concern I can not see it was in any way applicable here. |
Originally Posted by Bpalmer
(Post 8684910)
My own A330 simulator trials of recovery after the stab trim was full nose up and the stall fully developed was that a prolonged nose down input did help—but only initially. However, as the angle of attack reduced and the speed increased, apparently the full nose up stab was more than the elevator could overcome and the airplane pitched up regardless of the nose-down stick position.
It's not clear if the autopitch trim was operational with questionable airspeed inputs, but despite high bank angles in an attempt to keep the nose low, recovery was not achieved until I reduced the stab trim manually. Once trim was reduced manually, pitch control resumed and recovery was possible. http://www.pprune.org/tech-log/46062...ml#post6793521
Originally Posted by me
So, I was talking about some research this weekend. I got in touch with an old Aero Engineering pal of mine from Uni and he managed to wangle us some spare sim time at his facility in the wee hours inbetween training sessions. What we had was an A320 sim rather than an A330, which comes with some key differences - the most obvious of which is the lack of Alternate 2, the nearest equivalent being Alternate without speed stability, and a different underlying architecture past a certain point.
Due to time constraints we could only run each experiment once, preceded by some familiarisation time handling the sim manually in Normal Law, albeit at low level, following the FDs around basic turns and level changes. 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. Of course, these were purely technical experiments. Not only was this a sim session with only pride at risk, but we all knew what was coming and had a pretty good idea of how to get out of it. This does not and cannot compare to a situation where you're trying to get out of it for real, especially with the added handicap of limited manual flying experience. Whether the A330 behaves differently I don't know, but I've called in my favours for now and am eternally grateful to the people who made it possible. Someone else is going to have to take that on. In your experiment, did you fail all 3 ADRs at the same time? This would put the aircraft into Direct Law and fail the autotrim - which might explain why your trim wheel didn't roll forward with sustained nose-down stick in the way ours did. @Winnerhofer - they're pilots, not dogs. You can't force behaviour just by making things more difficult for them. The THS position would have been a moot point if the PF hadn't made significantly inappropriate pitch inputs for that phase of flight. |
@OK465 - Really? Fair enough. I'd swear I remember something like that in my reading though... I know you lose Yaw Damping with triple ADR failure. I guess I'm just trying to figure out why the trim rolled forward in our experiments and not in Brian's.
EDIT : Ah - Failing all three IRs get you Direct Law, not the ADRs. |
Dozy
The THS position would have been a moot point if the PF hadn't made significantly inappropriate pitch inputs for that phase of flight. The only solution other than use his brain is physically preventing a way to do this action (as is sometimes done in the industry in general .. restricted movement of limbs or safety guards .. barriers) which is virtually impossible in aviation On the other hand one can also ask the onboard artificial intelligence to play the role of safety guard For example .. why embedded intelligence leaves THS do what he wants (following a bad pilot action) that is to say foster the rise ... while she know that the airplane is near its maximum allowable alltitude (from some parameters ... weight .. engine power altimeter .. air temperature .. etc. ..) and when that maximum height is reached ... she keeps in position THS to continue climb |
@jcj: The system is not intended to be of the level of complexity required to determine "bad" inputs from "good" ones. The whole ethos of the Alternate Law system is to give the pilot as much control as possible while keeping as many systems online as it can. The A320 appears to have a limit on trim travel in Alternate Law, but - possibly as a result of press/professional backlash at maintaining authority, the A330's THS system gives the pilot complete authority at all times. One can't have it both ways.
@Winnerhofer: Perpignan isn't really comparable - in that case the AoA vanes failed due to water ingress from improper cleaning methods, which froze at altitude. The acceptance pilots also broke from the specified procedure when testing the safety features. In the case of AF447, every component in a technical sense (bar the problematic pitot tubes) was working correctly. |
OK465, thank you for providing some answers to my questions.
OK465 From the simulations I've seen, it appears that the pitch gains are permanently fixed for 330 KIAS regardless of whether the speeds become valid again or not, OK465 I'm completely out of the business now, but with respect to all this discussion of simulator post stall behavior and subsequent recovery in a simulator, the last communication I read from a noted sim manufacturer stated that beyond a relatively early point in the sequence, as opposed to 'flying', one is simply operating a high dollar video game. |
Originally Posted by RetiredF4
(Post 8686456)
That part [sim stall behaviour not necessarily following the real aircraft] made my day! Hope, Dozy reads it as well.
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Good to see the old denizens of this thread at it again. And I welcome Mssr Palmer ( wish he was here years ago).
- Good posts, Retired. And I hope the bus drivers that took issue with me years ago about gee command versus pitch command note your post and Palmer's. Viper "standby gains" were maybe a consideration by the 'bus folks in their design stage. We had a similar speed as the 'bus with gear up and something like 180 knots CAS with gear handle down. - the gee command in the 'bus has a pitch attitude compensation, right? So neutral stick might be commanding other than 1 gee ( Nz), unlike our system ( simple and many less degraded modes and sub-modes). So maybe this function was in play, as the nose was fairly high all the way down. Thots Mssr Palmer? - I agree with Winner about a simple degredation sequence. I would guess most 'bus drivers do not know all the stuff that continues and changes to stuff until they get to "direct" laws. - I agree that the overspeed concern is not warranted. The jet design seems very good, witness the stall with no violent wing rock or shaking or.... So I feel it could easily get up to 0.9 or a bit above without a flutter problem or even aileron reversal ( spoilers a big help in that regime). |
@jcj: The system is not intended to be of the level of complexity required to determine "bad" inputs from "good" ones What is the disadvantage (or danger versus the existing system ... THS stay full climb) of establishing such an automatic ? Is a automatism could decide the fate of the aircraft before the laws of physic ( Newton law is one) "take command" ? |
I find some doubts being expressed on auto trim function during unstalling the aircraft. AF 447 remained in alternate2 and never went into direct law so auto trim will function. In Perpignan crash after the crew dropped the speed(purposely for test) it changed to direct law as they lowered the gear and since AoA were frozen they gave erroneous inputs it had trimmed full up. This would need manual forward trim to unstall.During stall exercise with gear down in direct law you do not trim below Vls for the same reason.As they were only at 4000ft and were under lot of pressure they didn't figure that out. In AF447 the stick input to reduce the pitch was never sustained for any length of time. His actions were more like he believed in displayed vertical speed.He would push forward for whatever reason but watching the VS would pull back. So the stabilizer would stay up. He seems to have taken stall recovery action as taught that time with emphasis on minimum loss of height, rather than unreliable speed procedure. It is apparent he never looked at the PFD otherwise he would have lowered the nose at least on the horizon and let it be there for a while.
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otherwise he would have lowered the nose at least on the horizon and let it be there for a while. |
Hello Mr Palmer;
My own A330 simulator trials of recovery after the stab trim was full nose up and the stall fully developed was that a prolonged nose down input did help—but only initially. However, as the angle of attack reduced and the speed increased, apparently the full nose up stab was more than the elevator could overcome and the airplane pitched up regardless of the nose-down stick position. In my own sim trials the elevators were sufficient to initially achieve about a 10-deg ND pitch attitude, and the THS always began returning to normal when the stick was held full-ND. I agree that recovery was probably not possible unless/until the THS returned to a normal setting. A manual setting of the THS was always available to the AF447 crew but it would have returned to the NU position once the manual rotation of the wheel stopped - by that time, they may have got the wing unstalled. In our trials it took about 20,000ft, about 45 seconds. |
Originally Posted by PJ2
(Post 8687719)
In my own sim trials the elevators were sufficient to initially achieve about a 10-deg ND pitch attitude, and the THS always began returning to normal when the stick was held full-ND.
A manual setting of the THS was always available to the AF447 crew but it would have returned to the NU position once the manual rotation of the wheel stopped Correct me if I'm wrong, but I think trim logic is set by stick demand, attitude and time, so as long as the stick was held forward while the trim wheel was rolled forward, I don't think you'd see a significant return to NU. |
Dozy;
In the small amount of research I did a while back I had the impression that so long as the airplane wasn't in Direct Law, and the auto-trim system was functioning normally, one could set trim using the wheel because the system senses a manual input and releases the brake on the hydraulic motor driving the THS. Once that motion was no longer sensed, to me it was logical that the system would return to normal and try to satisfy whatever orders were being received by other systems. Some have said that order is the 1g order and so we may have seen a return to the -13deg setting, or, if the stick had been full-forward for sufficient time, it would have returned enough to provide elevator authority sufficient to reduce the AoA and unstall the wing. All theory of course... In direct law we know it is a different story; that's why the red ECAM warning. The design seems to boil down to the engineers imagining and expecting this scenario. Hindsight being what it is, we can now say something but I'll bet anyone here that no one imagined such a scenario to the point where the design would have been changed - certainly not the certification people. Just my personal opinion but to me that is entirely crystal ball territory. One of course cannot imagine and account for everything and still get the machine off the ground. |
DozyWannabe Correct me if I'm wrong, but I think trim logic is set by stick demand, attitude and time, so as long as the stick was held forward while the trim wheel was rolled forward, I don't think you'd see a significant return to NU. THS trim afaik is not driven by SS, but by elevator position. The SS demands a load factor change or a loadfactor of 1 g if stick is in neutral position. The Computers transfer this demand to an elevator deflection. The THS trim then moves to zero out this elevator deflection to restore the full elevator authority in both nose up and nose down direction. As ever there will be limits when this action starts, but i have these not handy. It would not be logical that the trim would start to move nose down when the elevator deflection is still in the nose up region, as was the case in AF447 for those moments when the crew made nose down inputs. Due to the increasing sinkrate the loadfactor was most times already below 1 g, therefore a small elevator change from full nose up elevator was enough to further decrease the loadfactor. I really would like to hear from AB what kind of input / maneuver would have been necessary to get this aircraft safely out of this well developped stall. Then we would have hard facts instead of reliance on some individual sim experiments, which might behave differently and lead to wrong conclusions. AB must have done those tests as well, where are the results? |
RetiredF4;
I understand your caution on sim experiments. However, I don't think we can dismiss simulator experience and performance entirely, out-of-hand. To focus on the item under discussion, the THS does not change its behaviour in a stall; it is responding to orders as before. I think it is reasonable to assume, (until proven otherwise by AB, an AMM or a true authority on the A330), that the simulator replicates the THS behaviour accurately. On the sink-rate 'g', I think it was very close to 1g all the way down - isn't that the definition of "falling"? Other than slight changes in pitch slightly increasing or decreasing 'g', why would it be "most times below 1g"? |
Hello PJ2,
yes i'm very cautious to the sim experiments, and especially due to the facts that such experiments or their results are not known from BEA or AB or from the main players in Simulator software or applications. There should be reason that they are not confident in the validity of any results after the stall was beyond its initial state. PJ2 To focus on the item under discussion, the THS does not change its behaviour in a stall; it is responding to orders as before. I think it is reasonable to assume, (until proven otherwise by AB, an AMM or a true authority on the A330), that the simulator replicates the THS behaviour accurately. If that would be the case, and i do not know if it is, then you would start your sim experiment stall recovery always with the same default data of 20°AOA and not from actual AOA. That is the typical "garbage in, garbage out" case. OK465 I'm completely out of the business now, but with respect to all this discussion of simulator post stall behavior and subsequent recovery in a simulator, the last communication I read from a noted sim manufacturer stated that beyond a relatively early point in the sequence, as opposed to 'flying', one is simply operating a high dollar video game. PJ2 On the sink-rate 'g', I think it was very close to 1g all the way down - isn't that the definition of "falling"? Other than slight changes in pitch slightly increasing or decreasing 'g', why would it be "most times below 1g"? From 2:10:27 until 02:10:50 (zoom phase) and from 02:11:03 until 2:12:00 the loadfactor was below 1 g. The timeframe with the positive g (02:10:50 until 02:11:03) kicked AF447 into the stall by some noseup stick and TOGA thrust. At 02:12:00 the jet was falling through FL 310 with an AOA of 45° After that point the loadfactor varied around 1 g. The sinkrate was increasing until passing FL 310. In normal flight that would be longitudonal acceleration, with high stall AOA it is sensed as vertical acceleration. If my math is right, then with AOA 30° sinus is 0,5 and with AOA 60° sinus is 0,866. Therefore increase of descent rate and increase of AOA both contributed to the loadfactor below 1g. I hope that clears up my wrong statement "all the way down". |
Hello RetiredF4;
We're on the same page I think, in fact I recall arguing against simulation of the stall for diagnostic purposes in the original threads for the very reasons described - there's no data and it is "here be dragons" land...as you say, GIGO, (however, I think that is changing). That said, I considered that the behaviour of the THS in response to orders from the stick, (which in turn was ordering the elevators) would not be affected by the stall and that is the only point I'm making. The THS would still respond "normally" to inputs on the stick, in other words, regardless of AoA, rates of descent, etc., etc. Also, it would still respond to manual input using the two wheels on the pedestal. Yes, your remarks regarding 1g clear that up, thank you. |
OK465;
Hear you...can't claim either "record" - did the exercise almost two years ago and that was that. There are sim guys out there whose company operates A330s who've done this tons of times because they're now teaching it and they're realizing the value of hand-flying in automated transports - a couple of good things to come out of all this. As for the rest, so long as the major factors which lie behind this accident are recognized, understood and the teaching has changed, then I believe the argued points are less critical. Beyond such understanding and change, it's our passengers who should "win". |
Originally Posted by OK465
I have seen THS action vary from run to run on a given day
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Option 1: don't disturb anything.
Option 2: in that fully developed stall tell the Captain what happened, put the nose to 40 degrees down and throttles to idle and fly from there. |
Any chance of a summary in English for us linguistically challenged anglos?
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Can we have this renamed to "AF447 thread No12" please? ................. Done .. JT
Originally Posted by G0ULI
(Post 8678662)
Side stick controls meant the cockpit could be made smaller allowing a bit more room for the passenger cabin and an extra row of seats.
Originally Posted by _Phoenix_
(Post 8678734)
But if the pilot is incapacitated, in a spiral dive 4g+, with thumb on priority switch...
Originally Posted by _Phoenix_
(Post 8678734)
In an aircraft with traditional controls, Robert would say "My airplane", then he would notice the colum moving in his lap. Probably he would say "listen Bonin, trust me I know what is wrong, give me the controls!"
Originally Posted by _Phoenix_
(Post 8678734)
Why the designers could get away without adding haptic feedback is a mystery and dual input is a hilarious stupidity.
Originally Posted by RetiredF4
(Post 8679007)
Boing is sticking to the old layout with tactile feedback. To assume they did it due to personal oppinion of their engineers or their pilots falls short considerably.
Originally Posted by CONF iture
(Post 8679905)
The Airbus concept or an obstacle to an otherwise natural tool for CRM optimization.
Originally Posted by tdracer
(Post 8680205)
Bonin lacked the most fundamental understanding of how airplanes work
Originally Posted by Machinbird
(Post 8681574)
To properly run the hands off scenario, about the best one can do is to do a long series of simulations with random turbulence injected to see where the most probable result lies
Originally Posted by Machinbird
(Post 8681574)
One thing you can hang your hat on is that the resultant flight path in Fig 64 is only a speculative path that starts with closely similar winds aloft and diverges from what would have been encountered had the hands free course been taken.
Originally Posted by RetiredF4
(Post 8681776)
the roll excursion was changing from left to right (like wing rocking) despite the inputs Bonin made.
Originally Posted by RetiredF4
(Post 8681776)
Bonin was obsessed in geting the roll under control, causing PIO by his inputs in roll direct, and thus not gave much attention to the pitch excursion.
Originally Posted by Machinbird
(Post 8683048)
The art of hand flying an aircraft has certain elements to it that are common across a wide range of aircraft.
Originally Posted by Bpalmer
My own A330 simulator trials of recovery after the stab trim was full nose up and the stall fully developed was that a prolonged nose down input did help—but only initially. However, as the angle of attack reduced and the speed increased, apparently the full nose up stab was more than the elevator could overcome and the airplane pitched up regardless of the nose-down stick position.
Originally Posted by RetiredF4
If the fixed gains are for 330 KIAS and the jet is in a low speed situation, then the resulting flight control deflections would be minimal in relation to that if the gains would be set for the actual slower speed. Did i get that right?
Originally Posted by RetiredF4
The position of the SS commands a loadfactor (g) demand, not a pitch demand. With SS neutral the value is known to be 1 g. SS Nose down demands less than 1 g, SS nose up demands more than 1 g. At low speeds the command is a pitch rate change. AFAIK we still do not know, what the preset rates for those changes are per unit SS deflection, and how the speed changes the preset gains.
Originally Posted by gums
the gee command in the 'bus has a pitch attitude compensation, right?
Originally Posted by RetiredF4
AB must have done those tests as well, where are the results?
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THS gubbins...
Hey all - sorry, been a bit unwell the last few days.
Anyhoo - I found A33Zab's post from back in the fourth thread, which I hope can shed some light on the THS question. Link here: http://www.pprune.org/tech-log/45465...ml#post6532375 It's worth having a look at the whole thing, but the interesting bit that I recall is this: From study material and answer to Machinbird's question: "An override mechanism, which is installed in the PTA (Pitch Trim Actuator), makes sure that the mechanical control through the trim wheels cancels the electrical control. When a manual command is made with the trim wheels, the override mechanism gives priority over the electrical command from the FCPCs. It mechanically disconnects the PTA output from the mechanical input (via electro-magnetic clutch) and also operates the overriding detection switches which in turn signal the FCPC's to stop any electrical command from the FCPC's." As to the other question - i.e. what the FCPC is doing with the various inputs (elevator position, stick input etc.) while the trim is being controlled manually - either it continues computing where it wants the THS to be while the wheel is under manual control - in which case the electrical system will attempt to re-acquire that on release, or it does not - and simply starts calculating from the point the wheel is released. In either case it will not attempt to roll it back to the last known position, and in the former case it will not roll it all the way NU unless the sidestick has been commanding that position while the wheel has been under manual control. |
@Winnerhofer - appreciate the enthusiasm, but it might be worth checking to see if the subject of AoA gauges has been brought up in the previous threads before posting it again (for the record, it has)...
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Human error, human factor
Originally Posted by Winnerhofer ref Waldo Cerdan
Thus, human error is reconfirmed as the prime cause of the accident because the pilots failed to identify and properly manage a problem already known to exist in such conditions
John Tullamarine's excellent document about human factor, or part of the USAF KC-135R report refering to human factor (excellent too) are going to the deep of human factor definition, very far from the pseudo-philosophical and pseudo-scientific readings i.e. that quotation and other VF! |
Clandestino:
Good to see you back in the scrum. :ok: Just a thought here ... Remembering any of it at 4AM when scared witless is not quite so. Captain DuBois may have been indicating fear with his "it's not possible" remark, but he just as likely to have been in a different mode of problem solving as he tried to get a grip on what those two had done in his absence ... and correct it. His instructions to Bonin on using his rudder to help his roll control strikes me as being in a problem solving mode, not in the "I am scared" mode as he tried to get the situation back to something like normal. The above considered, we can't be sure since we can't read minds through a CVR, and can't read minds beyond the grave. We'll never know if they were frightened or not. I don't think they ever got to that point. |
FBW auto trim implementation
Wrong, Winner. The pitch law is not for an attitude. The attitude resulting from a stick input and then neutral is due to the pitch gee factor that the engineers programmed.
Our primitive Viper law was all AoA limit and gee command. At 45 degrees of pitch, a neutral stick had about 0.707 gee thru your feet, but the jet kept trying for one gee Nz, and you kept getting more nose up attitude and the dreaded THS autotrim. The 'bus corrects for that in "normal" law ( and maybe one of the sub-laws). It also puts in a gee command for pitch when rolling into and continuing a turn. My opinion is too many protections and "aids" once the primary law is gone. Sheesh. Put a big light up and say "you are in back-up flight control law, and fly stick and rudder!" We don't need to go to "direct law" willy nilly. But trying to keep all the "protections" until finally in "direct" seems to create confusion for we pilots. |
Originally Posted by gums
(Post 8691135)
My opinion is too many protections and "aids" once the primary law is gone. Sheesh. Put a big light up and say "you are in back-up flight control law, and fly stick and rudder!"
Alternate law was activated by cutting ADR3 and activating ADR2 which was blocked (double ADR failure). The ALTN2B law triggered when the speed seen by Pitot 2 (via the drainage orifices) passed a certain breakout and the three ADRs became incoherent. This transition to ALTN2B being irreversible the valid speed information on PFD2 required for the rest of the flight was obtained by reactivating ADR3. 2.1.3.1.1 principal tests made and comments ... 2. Hand flying evaluation of flying qualities in ALT2B around 0.81M between 35000 and 38000 ft Pilot comments: ALTN2B didn't present any major difficulty of piloting. The control of attitude is pictures practically identical to that in normal law. The control in roll seems astonishingly more precise than normal law and the aircraft demonstrates a good and proper stability. When are more aggressive roll inputs are made there is a perception of lateral accelerations which could be interpreted as yaw. In summary, this ALTN2B law is not a factor which could justify a tunnel vision occupying all resources of the pilot. I didn't see any difference in the longitudinal control; the response to commands is correct; without action on the stick attitude remains stable |
The translation's rough and ready, admittedly - but it gives a reasonable overview for the most part. I think they actually physically blocked one of the pitot tubes before departure.
This was an A330-200 aircraft, and the report makes reference to using it to make certain that any claimed differences between that and the A340 previously tested would be nullified. |
I'm afraid Dozy rather jumped the gun there - my unpolished translation was a PV not intended for general consumption - well not yet anyway.
The complete, relevant French version is this: native French speakers feel free to correct my approximations! 2.1.3.1 Vol sur l’A330-243 MSN 1496 F-WWTP, le 10 février 2014 à Toulouse, en partie de nuit. Configuration particulière avion: (photo of blocked pitot) Tube de Pitot no2 bouché et son dégivrage inhibé pour tout le vol Configuration systèmes: ATA 27: FCPC P7/M16 ATA 31: FWC T1 La loi ALTN a été activée en coupant l’ADR3 et en activant l’ADR2 qui est boucheé (double panne d’ADR). La loi ALTN2B s’active alors lorsque la vitesse vue par le Pitot 2 (via les orifices de drainage) dépasse un certain seuil et que les 3 ADR deviennent incoherent. Cette transition en ALTN2B étant irreversible, on retrouve des informations de vitesse valable au PFD2 pour le bon déroulement des essaises, en réactivant l’ADR3 2.1.3.1.1. Essais principaux réalisées et commentaries 2. Prise en mains, evaluation des Qualities de Vol en loi ALTN2B, autour de M=0.81, entre 35000 and 38000ft. Commentaires pilotes: <<La loi de vol ALTN2B ne présente aucune difficulté majeure de pilotage. Le contrôle en assiete est pratiquement identique à celui de la loi normale. Le controle en roulis semble étonnament plus précis qu’en loi normale et l’avion fait preuve d’une bonne stabilité proper. Lorsque des impulsions plus aggressive en roulis sont effectuées, il en résulte une perception d’accélerations laterals pouvant etre interpretées comme des mouvements de lacet. En résumé, cette loi ALTN2B n’est pas un facteur pouvant justifier une <<vision tunnelisée>> accaparant toutes les resources du pilote,>> << Je n’ai ressenti aucune difference s’agissant du contrôle longitudinal, la réponse à la demande est correcte; sans action sur le manche, l’assiette reste stable.>> |
Nonsense
Originally Posted by "Experts"?
When […] more aggressive roll inputs are made there is a perception of lateral accelerations which could be interpreted as yaw.
Bonin was discovering that unknown law and that sudden law change and that behaviour dissimetry of the plane in pitch and roll. He was not informed -unlike the pilots of Toulouse's february 2014 flight- before the facts happened and was not a test pilot. Did anybody found objection in AF447's FDR/CVR? |
En résumé, cette loi ALTN2B n’est pas un facteur pouvant justifier une <<vision tunnelisée>> accaparant toutes les resources du pilote,>> In the reality ... over the sea at night in the AF447 .. the conditions were not the same ....... If you take all the events separately ... it's not so busy workload ... When you mix all the events in a short lap of time ... this is different ..... If you make a reenactment of the battle of Waterloo (with all the insight) maybe Napoleon will win ! |
Originally Posted by roulishollandais
(Post 8691550)
Bonin was discovering that unknown law and that sudden law change and that behaviour dissimetry of the plane in pitch and roll.
Sounds like making excuses to me... |
@DozyWanabee
The situation was lost after : -1 high altitude stall -2 wrong pitch-power used -3 inability to decide action after UAS -4 Autopilot missing -5 Captain leaving -6 Puzzled brain in a complex situation -7 Crew's Robert/Bonin bad coordination -8 Bad health/rest before the flight -9 ITZ -10 Missing stall test of airliner -11 etc. -12 Cadet training From my experience as airline pilot in a french airline, I would like to point the second and the fourth items. Really I only met people giving no importance to knowledge of some important ref pitch&power, included chief-pilot, instructors, etc. One of our CPL lost his ATPL check after being unable to continue safe MD83 ILS flight after he had to fly with Pitch and Power. It showed a gap of our pilots' team, but nothing was done. It was not only in high altitude. It is then that I revised for my own the page full of numbers and discovered the MacDonnell mistake N2% dicreased from 76 to 66 at 3000 Ft... It seems the wrong figure existed since 13 years, for 165 airlines... Happily nobody needed it. Perhaps the fact that the need of Pitch&Power seldom happens explains the deny of needing acurate knowledge, despite it is taught in old time french IFR BASICS ... |
@roulis:
Perhaps I should clarify. When I say "making excuses", I don't mean for the crew - I mean making excuses to blame the aircraft and systems. Of course being handed control via AP disconnect in cruise at night over the ocean and in turbulence is going to be a fairly difficult scenario for the pilot - even more so if that pilot has never been trained in or experienced handling the aircraft manually at that altitude. But that would be true of any aircraft type you care to name - whether the control layout is conventional or not, or whether the systems are electro-hydraulic or FBW (or indeed what control law one is in, in the latter case). The practice whereby pilots were routinely put into the flight deck in this phase of flight despite neither of them having any experience of manual handling in that scenario absolutely deserves close scrutiny - in real terms, it shouldn't really have been allowed to happen. What I was getting at was that it doesn't make sense to claim that the change in control law had any effect on the way he handled the aircraft (particularly in roll), or the way in which he perceived the aircraft to be handling - because he had no experience of what it was like normally with which to compare it and thus be "confused". Yes, it was probably frightening and yes it was difficult - but that was because of the scenario in which he found himself, not because of the change in control law. Does that make sense? |
Dozy;
Re, "Of course being handed control via AP disconnect in cruise at night over the ocean and in turbulence is going to be a fairly difficult scenario for the pilot" The following actually goes to your point regarding scrutiny, etc... Regarding being handed the airplane when the autopilot disconnects, no, it is not difficult at all, not even a bit. I've had the autopilot disconnect, (over both oceans...didn't seem to matter) and the first thing one does is leave it alone and do nothing, but (for those who desire to know what "do nothing" means), by all means maintain altitude and keep the airplane stabilized - most of the time it does that on it's own for a half a minute or so which is way more than one needs to assess the situation and get comfortable. Then try to re-engage the AP and if no joy, fly the airplane...tiny, gentle squeezes on the stick or column to correct little divergences. Hand-flying the aircraft in cruise IS difficult for anyone who hasn't done it or who doesn't have a lot of experience, and therein, as you say, is what needs scrutiny. In fact they shouldn't be in the cockpit but I recognize that I'm growing older and automation, (which I always thought was wonderful) is here to stay. I heartily agree that putting inexperienced (cadets?) people up front needs scrutiny - it's a money thing and is today somehow an acceptable risk). BTW, "...over the ocean" makes no difference, neither should night-time if one is an instrument pilot; the Airbus handles turbulence well when hand-flown in Normal law, (in fact you don't move the stick at all, really, until the airplane diverges from what one wants), and in Alternate law one is gentle with the airplane as a pilot would be with slightly more sensitive roll and at high altitudes. I have to say I've hand-flown the A330 & A340 in cruise, sometimes for an extended time, (not in RVSM airspace of course) and it's a delight aircraft to fly. The DC8 was a bit more of a handful in the sense that one was always "working the control column a tiny bit to maintain one's altitude, but it was just another airplane, difference was these aircraft have a lot of mass so they're slower to change, slower to return - one has to wait, then make a change, wait... They're all very stable and not difficult at all to fly. Flying them has less to do with training than one's experience - you can't "train" everyone to fly...that I know from experience, but if they can fly, then "training" would consist of little hints here and there regarding handling because you'd be expected to be able to fly an airplane. DP Davies was superb in the advice he offered. I tend to agree with you - an autopilot disconnect for someone without experience would be disconcerting and distracting. I think this is where the rubber meets the road, so to speak, in the way the industry has gone, and its already addressing the problem. |
@PJ2:
We're basically "singing from the same hymn-sheet" here. What I was getting at was the modern condition - that even a pilot with some experience of manual handling at high altitude may initially balk if it hasn't been practiced in a while. A pilot who has no such training or experience has every reason to feel genuinely scared. WRT "over the ocean/at night" etc. I was referring to the complete lack of outside reference for attitude, which I would imagine is a big deal in the event of an apparent instrument failure because it erodes trust in all the instruments, even those which are working. Anyways - all good... :ok: |
Not sure it's a "big deal" - it doesn't necessarily "erode trust in all the instruments" [my italics], especially not in those that are working - reason is, if you know they're working it is reasonable and probable that they can be trusted so you use them.
We experienced steadily diverging airspeed indications on a B767, (winter, in cloud, night, in the climb above FL200). We had to decide whether it was the captain's ASI or mine, as mine was getting lower and lower while he was maintaining a steady climb speed. Mine agreed with the steam-standby; the hiss of air noise wasn't normal. I wasn't flying at the moment so I don't know how the airplane felt - he began using the standby and as his ASI increased past the barber pole we waited for the overspeed warning - it never came, but an EICAS message came on regarding the ailerons and a speed limiting function, (I can't recall it now - it was amber). We took a look at the IRS/FMC groundspeed. He gave me control and we finished the flight uneventfully - the ASI returned to normal in warmer air during descent. No one here should mistake this for a hero story because it isn't - it's what's done very likely hundreds of times a day around the world in commercial transports- not this of course, but certainly something. It isn't thought of as "scary" or "difficult" - it's a problem to solve and with both good training and lots of time in, it usually works out. One should rarely if ever be scared in an airplane when s. happens but deeply respectful of what it may do to one if one provides it with an opening. When someone would ask how much airline pilots make, the joke was $100,000 a minute but you'll never know which one. Thing is, airlines aren't paying this anymore and now it's showing up, only occasionally so far, but as the cadets move to the left seat and the other seat is a 250hr guy or gal who's never just about killed themselves at least once, they're not up to snuff when things really get difficult. We live in an age that I call the "illusion of technique" because people who run things at airlines can be buffalo'ed into thinking technique is everything and neither experience nor intuition count for much anymore. I prefer to think of automation as the greatest assistant I've ever had except my First Officer and the two Relief Pilots - the machines are brilliant, but the guys and gals have eyes and got time in the old fashioned way and when their time comes they'll make great captains. I care very much about this profession and I don't like the trends; been writing about them for about twenty five years now - spit in the wind, and I'm a pilot who I loves automation. |
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