AF 447 Thread No. 6
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 82
Posts: 1,454
Likes: 0
Received 0 Likes
on
0 Posts
Wasn't the pitot-static system effectively completely hosed in the Perpignan case though (the systems must have been very badly compromised)? I must confess I didn't have an opportunity to follow that one closely at the time.
Perpignan accident was enabled when two AOA sensors froze at a low angle of attack while at altitude due to water intrusion. Crew later attempted to demonstrate activation of Alpha protect as part of a functional check flight of the aircraft and went well past into a full stall, autotrimming nearly full nose up in the process. Aircraft dropped into Direct Law (no autotrim) and crew was too busy to notice. High power setting plus nearly full nose up trim caused the nose to rise uncontrollably until stall. Did not pull out from the resulting nose down attitude.
The hated and feared autotrim, or not
Have been on the sideline too long watching defense of a poor control law reversion sequence versus a defense of a poor crew.
Gums' view is there is a lotta blame to spread about.
Take the auto trim, and I do not like that term.....
- When normally flying the jet, HAL tries to reduce required stick displacement from neutral in order to achieve 1 gee that is corrected for pitch. So at 30 degrees pitch, the thing tries to achieve 0.87 gee with hands-off the stick. If I don't read that part of the manual correctly, lemme know.
- If the pilot is commanding more than one gee ( corrected for pitch), then HAL trims the THS to reduce the required stick displacement, or am I wrong on that as well? I see no AoA command when looking at the manuals, but I see some "protections" and warnings that hinge upon AoA.
- If I am at a 15 degree pitch attitude and let go of the stick, then what does HAL do to maintain 0.96 gee as my speed decreases? Does HAL trim the THS for more nose up?
- Then there's AoA sensors that are ignored because the speed is below 60 knots. So how is the stall warning considered valid when the AoA was being ignored? What the hell are you going to use if airspeed indications are unreliable? Maybe replace all the stuff on the LCD screen with a crosshair and dot, then tell the crew to "center the do"t, huh? BEAM ME UP!
Deeply stalled, deep stall, just plain stalled..............
In a plane with a super wing design and great directional stability, then it is easy to be stalled and not spin or have severe wing rock. Buffet could be very low and/or masked by the local weather conditions.
I do not defend the AF crew for the continuous nose up commands, but I can understand the confusion once the jet was "deeply" stalled and various warnings were being presented.
The facts now present clear proof that one can stall the 'bus without going into a spin or having severe wing rock or buffet. Anyone disagree?
The facts do not show that a recovery from the flight condition I just mentioned is impossible, especially with a fully trimmed THS.
Show us the pitch moment versus AoA/CG graph.
I only joined this discussion because I had FBW experience way before the 'bus and was interested in the plane. I also thot I could add perspective from lessons-learned 15 years before the A320 flew.
If I am off base here, or considered a dinosaur that still insists upon mechanical feedback to my stick or wheel or yoke, then tell me to stay quiet.
Gums' view is there is a lotta blame to spread about.
Take the auto trim, and I do not like that term.....
- When normally flying the jet, HAL tries to reduce required stick displacement from neutral in order to achieve 1 gee that is corrected for pitch. So at 30 degrees pitch, the thing tries to achieve 0.87 gee with hands-off the stick. If I don't read that part of the manual correctly, lemme know.
- If the pilot is commanding more than one gee ( corrected for pitch), then HAL trims the THS to reduce the required stick displacement, or am I wrong on that as well? I see no AoA command when looking at the manuals, but I see some "protections" and warnings that hinge upon AoA.
- If I am at a 15 degree pitch attitude and let go of the stick, then what does HAL do to maintain 0.96 gee as my speed decreases? Does HAL trim the THS for more nose up?
- Then there's AoA sensors that are ignored because the speed is below 60 knots. So how is the stall warning considered valid when the AoA was being ignored? What the hell are you going to use if airspeed indications are unreliable? Maybe replace all the stuff on the LCD screen with a crosshair and dot, then tell the crew to "center the do"t, huh? BEAM ME UP!
Deeply stalled, deep stall, just plain stalled..............
In a plane with a super wing design and great directional stability, then it is easy to be stalled and not spin or have severe wing rock. Buffet could be very low and/or masked by the local weather conditions.
I do not defend the AF crew for the continuous nose up commands, but I can understand the confusion once the jet was "deeply" stalled and various warnings were being presented.
The facts now present clear proof that one can stall the 'bus without going into a spin or having severe wing rock or buffet. Anyone disagree?
The facts do not show that a recovery from the flight condition I just mentioned is impossible, especially with a fully trimmed THS.
Show us the pitch moment versus AoA/CG graph.
I only joined this discussion because I had FBW experience way before the 'bus and was interested in the plane. I also thot I could add perspective from lessons-learned 15 years before the A320 flew.
If I am off base here, or considered a dinosaur that still insists upon mechanical feedback to my stick or wheel or yoke, then tell me to stay quiet.
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes
on
0 Posts
gums. fwiw, I think you are in the money. As one of a rare few who continue to focus on the cause, rather than the effect, I for one appreciate the lead up to STALL that you discuss. For good or ill, and regardless of 'Blame', this a/c STALLED first, then it died. I like your basics approach, and 'ancient' pov.
if789. At what AoA did the first STALL WARN activate? To me, it seems a bit notable that at cruise, the STALL WARN activates. Since it occurs in such proximity to the a/p loss, my question would be what prompted the autoflight to approach Vs? Was it legit? Had the speeds gone south and the WARN was bogus? Was the vane compromised at this point? Thanks.
if789. At what AoA did the first STALL WARN activate? To me, it seems a bit notable that at cruise, the STALL WARN activates. Since it occurs in such proximity to the a/p loss, my question would be what prompted the autoflight to approach Vs? Was it legit? Had the speeds gone south and the WARN was bogus? Was the vane compromised at this point? Thanks.
Join Date: May 2011
Location: here
Posts: 131
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by gums
The facts now present clear proof that one can stall the 'bus without going into a spin or having severe wing rock or buffet. Anyone disagree?
Originally Posted by BEA report #3
This modification of the behaviour in the load factor at the centre of gravity results in the
appearance of a high frequency component of an amplitude increasing to until about 0.1 g
peak-to-peak, and with a signature that is very different from a turbulence signature of
meteorological origin. Moreover, there is a noise on track 1 of the CVR, at about 2 h 10 min
55, which might be the impact of the microphone striking a wall, heard at a stable frequency.
Note: According to the simulation of the aircraft movements, at this time the turbulence observed in the
first seconds of climbing had stopped.
Additional analyses were conducted with Airbus to determine if this phenomenon could
correspond to buffeting. The difficulty with identifying this phenomenon lies in the fact that, on
the one hand, the concept of buffeting is defined as accelerations at the pilots seats and not
at the centre of gravity and that, on the other hand, no flight test has been conducted under
conditions that correspond exactly to those of the event (particularly in terms of Mach).
Note: Examination of flight test data revealed, based on the frequency and amplitude, that this
signature could in fact be that of buffeting. By drawing analogies with the flight tests, the amplitude of
0.1 g at the centre of gravity suggests that the amplitude of the buffeting at the pilot seat is high
(approximately 0.6 g peak to peak).
appearance of a high frequency component of an amplitude increasing to until about 0.1 g
peak-to-peak, and with a signature that is very different from a turbulence signature of
meteorological origin. Moreover, there is a noise on track 1 of the CVR, at about 2 h 10 min
55, which might be the impact of the microphone striking a wall, heard at a stable frequency.
Note: According to the simulation of the aircraft movements, at this time the turbulence observed in the
first seconds of climbing had stopped.
Additional analyses were conducted with Airbus to determine if this phenomenon could
correspond to buffeting. The difficulty with identifying this phenomenon lies in the fact that, on
the one hand, the concept of buffeting is defined as accelerations at the pilots seats and not
at the centre of gravity and that, on the other hand, no flight test has been conducted under
conditions that correspond exactly to those of the event (particularly in terms of Mach).
Note: Examination of flight test data revealed, based on the frequency and amplitude, that this
signature could in fact be that of buffeting. By drawing analogies with the flight tests, the amplitude of
0.1 g at the centre of gravity suggests that the amplitude of the buffeting at the pilot seat is high
(approximately 0.6 g peak to peak).
@DW
DW
@Franzl
You're comparing apples with oranges here, or to be more literal, comparing the conventional, or "way we used to do it" method with the method on the FBW Airbus series, which is intended to be used in a completely different way - unless something has gone so seriously wrong with the aircraft that a drop to Direct Law is necesssary.
@Franzl
You're comparing apples with oranges here, or to be more literal, comparing the conventional, or "way we used to do it" method with the method on the FBW Airbus series, which is intended to be used in a completely different way - unless something has gone so seriously wrong with the aircraft that a drop to Direct Law is necesssary.
Quote DW (bolding by me)
It does exactly what it says on the tin and trims automatically in the same way that manual trim is applied on older aircraft - there have never been any hard limits on manual trim wheels, why should there be one on their modern automatic descendents?
It does exactly what it says on the tin and trims automatically in the same way that manual trim is applied on older aircraft - there have never been any hard limits on manual trim wheels, why should there be one on their modern automatic descendents?
Quote:
Originally Posted by DozyWannabe
Under all laws - even without protections, as the speed decays the control mode gradually transfers from "G" command to pitch command, meaning that the autotrim will not trim to stall with stick neutral due to decaying speed alone.
Originally Posted by DozyWannabe
Under all laws - even without protections, as the speed decays the control mode gradually transfers from "G" command to pitch command, meaning that the autotrim will not trim to stall with stick neutral due to decaying speed alone.
infrequentflyer
Not sure your're right there. Perpignan traces show exactly what you say can't happen.
I think you'll find that as speed decays, more elevator / trim will be needed to maintain stable attitude, and autotrim will happily provide it - up to the stops
Not sure your're right there. Perpignan traces show exactly what you say can't happen.
I think you'll find that as speed decays, more elevator / trim will be needed to maintain stable attitude, and autotrim will happily provide it - up to the stops
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 81
Posts: 1,330
Received 0 Likes
on
0 Posts
Originally posted by gums ...
Then there's AoA sensors that are ignored because the speed is below 60 knots. So how is the stall warning considered valid when the AoA was being ignored?
Then there's AoA sensors that are ignored because the speed is below 60 knots. So how is the stall warning considered valid when the AoA was being ignored?
The Stall Warning is just that, and if it was to serve its designed for purpose, the PF/PNF would be expected to acknowledge it and take appropriate action. They didn't, and the wheel turned and got them in the a*se. So in that respect you can't blame the SW.
The PF not understanding that the pitch operates the same way in Normal Law and Alternate Law, but one "is protected" and the other is "not protected" is also a mystery. The PNF more worried about getting the CPT back to the FD than calling the ECAM and getting the QRH out is an even stranger mystery. This accident didn't happen in a vacuum - it happened to a flight that was under the control of two "apparently" competent pilots.
Granted there are issues that have validly been raised in respect of the SS visibility, but they are secondary to the human factor failures that we are currently aware of.
Pitch Characteristics - Normal and Alternate Laws
When acting on the stick the pilot commands a constant G load maneuver and the aircraft response is G load / Pitch rate. The pilot order is therefore consistent with the aircraft response "naturally" expected by the pilot, Pitch rate at low speed / Flight Path rate or G at high speed
When acting on the stick the pilot commands a constant G load maneuver and the aircraft response is G load / Pitch rate. The pilot order is therefore consistent with the aircraft response "naturally" expected by the pilot, Pitch rate at low speed / Flight Path rate or G at high speed
Lets face it, the pilots had control and the aircraft knew no better than to obey them.
Last edited by mm43; 2nd Nov 2011 at 18:48. Reason: grammar
Control
mm43
Lets face it, the pilots had control and the aircraft knew no better than to obey them.
Lets face it, the pilots had control and the aircraft knew no better than to obey them.
Lets face the fact, that this knowledge probably was not present with the crew of AF447. And unfortunately the discussions in this and the former threads show, that it is not a single case problem.
Originally Posted by Retired f4
That is exactly what happens, and i cannot understand, how anybody can feel good about it.
Originally Posted by Retired F4
Lets face the fact, that this knowledge probably was not present with the crew of AF447
I have to make very long&imprecise shot here: I suppose that in former life you were jealous of Bitburg based Ego drivers, with right hand gloves that didn't show wear at thumb.
Translation: F-15 has autotrim. How can anybody fell good about it? Very easily, I'd say.
Originally Posted by mm43
Granted there are issues that have validly being raised in respect of the SS visiblity
Last edited by Clandestino; 2nd Nov 2011 at 12:35. Reason: Part of the post lost in translation first time around.
clandestino
Hi Clandestino,
I have a chuckle on this one, like it actually. I still have some left hand gloves in good shape and missing the right ones with holes in the thumb.
I was flying in the backseat of an F15 double seater 1990 in a low level mission, and didn´t even recognize its autotrimming.
But to make my position clear: I stated several times and do it again here, i have nothing at all against a fine autotrim system. So its a bit unfair of you to put blame on me for not recognizing the advantages of FBW and its asociated systems.
I agree with that, never did otherwise, and i knew somebody would jump on it. My concern is not about blame (neither to the pilots nor to the airframe), but about prevention. This trimsystem can be improved in the mentioned area without decreasing its overall performance, thus eliminating one hole in the different layers of cheese.
Why not talk about it and why not work on a change? Is it pride or neglicence, costs or arrogance which keeps us from recognizing, that there was a crew who was obviously not familiar with the behaviour of the aircraft despite their training, their hours of experience and their legal licences? Im pretty sure, there are others out there who learned a lot out of this accident and try to improve their knowledge base, but others will not and will never and might fall to the same situation.
Why not improve the autotrim system? There are accidents (not this one alone) where a correct functioning autotrim, not understood by the crew, contributed to the outcome of the happening. That should tell us not only that knowledge and training has to be improved, but that we also should improve the system to prevent that such misinterpretations proliferate into full accidents.
The statement, that they shouldn´t have got in this situation beforehand is correct, but it is not the way to look at the things in accident investigation and accident prevention and in view of flight safety. The task is not to close the hole in the first layer of cheese, but to take care of all known holes.
I have to make very long&imprecise shot here: I suppose that in former life you were jealous of Bitburg based Ego drivers, with right hand gloves that didn't show wear at thumb.
I was flying in the backseat of an F15 double seater 1990 in a low level mission, and didn´t even recognize its autotrimming.
But to make my position clear: I stated several times and do it again here, i have nothing at all against a fine autotrim system. So its a bit unfair of you to put blame on me for not recognizing the advantages of FBW and its asociated systems.
There! You have effectively answered yourself; autotrim is good thing as long as one know how it works, applicable to any aeroplane system and one is required to know that by air law and the basic DNA-ingrained law of self preservation. With AF447 crew it was not just that they forgot about autotrim - they never verbalized what in the hell they thought was going on and what they thought they should do, indicating the rabbit-in-the-headlights defence posture. In the end, what CM2 did with the stick is what killed them. Investigation did not find a single reason why trim would go AND if only stick were pushed forward.
Why not talk about it and why not work on a change? Is it pride or neglicence, costs or arrogance which keeps us from recognizing, that there was a crew who was obviously not familiar with the behaviour of the aircraft despite their training, their hours of experience and their legal licences? Im pretty sure, there are others out there who learned a lot out of this accident and try to improve their knowledge base, but others will not and will never and might fall to the same situation.
Why not improve the autotrim system? There are accidents (not this one alone) where a correct functioning autotrim, not understood by the crew, contributed to the outcome of the happening. That should tell us not only that knowledge and training has to be improved, but that we also should improve the system to prevent that such misinterpretations proliferate into full accidents.
The statement, that they shouldn´t have got in this situation beforehand is correct, but it is not the way to look at the things in accident investigation and accident prevention and in view of flight safety. The task is not to close the hole in the first layer of cheese, but to take care of all known holes.
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by RF4
There are accidents (not this one alone) where a correct functioning autotrim, not understood by the crew, contributed to the outcome of the happening.
Last edited by HazelNuts39; 2nd Nov 2011 at 12:52.
Hazelnuts39
I might try.
At 02:10:51 the stall warning sounded. AOA was 6°, pitch was 10°, elevators about 5° noseup, THS at -3° NU. At that point the stab trim starts taking over the load of the elevators and the THS trim starts to move uninterrupted to full NU position within the next minute. During this time period the SS was in the average NU, but never full NU (max NU was 13°, 5 times it was up to 8° ND. Note, that the elevators stayed at max 10° NU until 02:11:35: Then they moved further down and reached their 30° NU at 02:11:45 and about the same time the THS reached the full NU limit. (see the FDR in the BEA interim 3 report).
Would this THS trimming had been prevented upon the sounding of the stall warning, the elevators alone would have imho not been sufficient to keep the nose up in the stall over the following period. This THS is a mightiy thing and gave the crew the tool, to transfer their unfortunate SS commands into some kind of establishing the aircraft deep into the stall region.
The nose woud have dropped early in the stall, maybe the AOA would have been considerably lower and thus permanent stall warning available, the speed drop would have been less and all this could have finally helped in an recovery (which unfortunately was even not attempted).
I´m not saying, that this would have prevented the outcome at all, but it might in another situation on another day with a different crew.
At 02:10:51 the stall warning sounded. AOA was 6°, pitch was 10°, elevators about 5° noseup, THS at -3° NU. At that point the stab trim starts taking over the load of the elevators and the THS trim starts to move uninterrupted to full NU position within the next minute. During this time period the SS was in the average NU, but never full NU (max NU was 13°, 5 times it was up to 8° ND. Note, that the elevators stayed at max 10° NU until 02:11:35: Then they moved further down and reached their 30° NU at 02:11:45 and about the same time the THS reached the full NU limit. (see the FDR in the BEA interim 3 report).
Would this THS trimming had been prevented upon the sounding of the stall warning, the elevators alone would have imho not been sufficient to keep the nose up in the stall over the following period. This THS is a mightiy thing and gave the crew the tool, to transfer their unfortunate SS commands into some kind of establishing the aircraft deep into the stall region.
The nose woud have dropped early in the stall, maybe the AOA would have been considerably lower and thus permanent stall warning available, the speed drop would have been less and all this could have finally helped in an recovery (which unfortunately was even not attempted).
I´m not saying, that this would have prevented the outcome at all, but it might in another situation on another day with a different crew.
Last edited by RetiredF4; 2nd Nov 2011 at 12:48.
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes
on
0 Posts
There is a bottom line in that conjecture, one I posted a very long time ago. It hasn't to do with competence of pilotage, but with common sense from the supposed brilliance of the design. "Just like a "Conventional" Aircraft", is buspeak for "Let's throw a bone." Arrogant.
Had the a/c STALLED earlier, without the authority of that monster slab, there would have been a great deal more energy retained, and the Nose would have fallen dramatically, imo.
Instead of MUSH, the pilots would have had at least one emphatic cue. Wait, let's make that two, with proper Buffet. Whether at that point the flight recovers is moot.
But it's worth an honest discussion.
Had the a/c STALLED earlier, without the authority of that monster slab, there would have been a great deal more energy retained, and the Nose would have fallen dramatically, imo.
Instead of MUSH, the pilots would have had at least one emphatic cue. Wait, let's make that two, with proper Buffet. Whether at that point the flight recovers is moot.
But it's worth an honest discussion.
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes
on
0 Posts
RetiredF4;
Thanks for your elaborate explanation, with which I partially agree, but not quite. The airplane stalled a few seconds before 02:11:00, when the THS had hardly moved. The longitudinal control law imposes a certain pitch rate in response to the SS demands. If the THS had not moved, that pitch rate would have required a larger deflection of the elevator, but the pitch rate and hence AoA achieved would not have been significantly different, until the elevator reaches its stop. As to the THS being 'a mighty thing', that is true, but should not be exaggerated. According to Owain G's post, 10 deg of THS is equivalent to 15 deg of elevator. Therefore I agree that the effect of less THS as the airplane got deeper into the stall would have been somewhat lower AoA's, but that's about it.
Thanks for your elaborate explanation, with which I partially agree, but not quite. The airplane stalled a few seconds before 02:11:00, when the THS had hardly moved. The longitudinal control law imposes a certain pitch rate in response to the SS demands. If the THS had not moved, that pitch rate would have required a larger deflection of the elevator, but the pitch rate and hence AoA achieved would not have been significantly different, until the elevator reaches its stop. As to the THS being 'a mighty thing', that is true, but should not be exaggerated. According to Owain G's post, 10 deg of THS is equivalent to 15 deg of elevator. Therefore I agree that the effect of less THS as the airplane got deeper into the stall would have been somewhat lower AoA's, but that's about it.
Retired F4, I did not mean to infer that we shouldn't be discussing the Airbus flight controls in general or autotrim in particular; quite the opposite - it absolutely needs to be discussed to gain understanding. Given your experience and information you posses, your points are very valid and true. However, methinks that your perspective is somewhat lacking breadth. It is indeed true that having autotrim stop at stall warning would make AF447 behave differently - whether it would significantly affect the outcome is open to conjecture. Problem is we don't have infinite amount of cheese to patch up all holes. Patching up one, more often than not opens other holes. As DP Davies has beautifully demonstrated when analyzing pushers, every safety system is potential killer and risks an benefits have to be weighed carefully, especially cases of "operating when not needed" vs. "failing to operate when required". Before AF 447 there was nothing to suggest that autotrim concept as applied to FBW Airbi is flawed and I guess that even after final report is out it won't change.
It actually is but is not be-all and end-all. Obedient trim has good chances to be listed as one of fifity-something or more contributing factors but we shouldn't concentrate solely or it or ignore it completely. Balance has to be struck somewhere, not necessarily in the middle. As I see it, it was just a footnote in the history of certain crew that became (in)famous through spectacular error.
The biggest problem I see in discussions regarding the unwholesome fate of AF447 is that we are faced with horrible picture of three pilots who forgot how to fly in the midair so we are amusing ourselves with tiny technical details just to avoid to step back and face the sheer ugliness of the event.
Did I just blame the deceases pilots for the calamity? On purely technical grounds: no! I don't care a little bit about earthly theories of fault and blame but I do want that whatever daemon of the air got our unlucky colleagues gets caught and dissected and we won't be able to catch it if we put our traps in the places it doesn't visit.
It's not technical, it's in our heads.
The statement, that they shouldn´t have got in this situation beforehand is correct, but it is not the way to look at the things in accident investigation and accident prevention and in view of flight safety.
The biggest problem I see in discussions regarding the unwholesome fate of AF447 is that we are faced with horrible picture of three pilots who forgot how to fly in the midair so we are amusing ourselves with tiny technical details just to avoid to step back and face the sheer ugliness of the event.
Did I just blame the deceases pilots for the calamity? On purely technical grounds: no! I don't care a little bit about earthly theories of fault and blame but I do want that whatever daemon of the air got our unlucky colleagues gets caught and dissected and we won't be able to catch it if we put our traps in the places it doesn't visit.
It's not technical, it's in our heads.
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 82
Posts: 1,454
Likes: 0
Received 0 Likes
on
0 Posts
Before AF 447 there was nothing to suggest that autotrim concept as applied to FBW Airbi is flawed and I guess that even after final report is out it won't change.
I don't know much time you have in tactical jets, but you have enough chutzpah to have come to aviation that way. This is not a criticism by the way.
The performance of the autotrim system in this corner of the flight envelope likely does not meet certification requirements. Certifying this feature in Alt 2 at the stall was probably not envisioned in the initial requirements due to the high anticipated reliability of the airspeed system. It fell under the category of too improbable to worry about. Today we know that line pilots actually bumped into this corner of the envelope.
Despite Owain's assertions about relative power of the elevator versus HS (and I believe he is quite competent in this field) he was not working with the best data and his results may be slightly skewed.
Consider the Perpignan A320 and how throughly the THS overruled the elevator. Different aircraft, but designed by the same team with similar design philosophy.
Yes it is possible to stall the Bus in ALT2 using just elevator and thrust as we saw demonstrated by AF447, but who can say, had the trim had been limited, whether or not the crew would have seen the airspeed come off the peg a bit during one of their nose down trials and continued their nose down efforts.
THS running full nose up is a potential serious hazard and needs to be guarded against better. How to do that is one for the engineers (design type not wrench type) to puzzle out, but judging from what has recently transpired with the type, it may save two or more aircraft in the future. Expecting training to handle the problem completely is not realistic. If we see nothing in BEA's final accident report addressing this problem, then you should be concerned.
Last edited by Machinbird; 2nd Nov 2011 at 15:27.
SS inoperative
When reviewing the FDR traces for my last contribution i stumbled on the the bottom lines on page 108 of BEA interim report N. 3.
At about 02:11:40 their is a spike indicating FO SS inoperative and a longer one shortly thereafter with Captain SS inoperative. It happens the same time, the THS and elevators reached Full Nose up. At the end the same indication Capt. SS inoperatie shows up again.
WHat would have caused this indication? Has it something to do with the priority button?
At about 02:11:40 their is a spike indicating FO SS inoperative and a longer one shortly thereafter with Captain SS inoperative. It happens the same time, the THS and elevators reached Full Nose up. At the end the same indication Capt. SS inoperatie shows up again.
WHat would have caused this indication? Has it something to do with the priority button?
Machinbird, in re training:
The THS can be limited in movement by using the hand wheel in the cockpit. If it goes up too far it can be moved back down to where the pilots want it, since it appears that hands on the wheel overrides anything HAL tells it to do ... at least while the hand is on the wheel. 
Some threads ago, one of our Airbus 330 experienced pilots indicated that touching of the trim wheel in some sim training sessions was incentivized against. (Training note: This looks to fall into the realm of something called negative training, as in not correctly incentivizing a proper course of action, or incentiving against a given course of action).
Yet another Airbus 330 experienced poster here, Mikelour IIRC, described some unusual attitude training he encountered where using the trim wheel was one of the best ways to deal with it, though some crews had to be coaxed into using that resource, see above for possible reasons for that.
There seems to be some professional disagreement within the AB community, and the people who train the crews for various companies, on what is and isn't appropriate use of the trim wheels.
I don't think that changes the response to your concern:
if THS runs amok, you can manage it with your hand. What seems to add joy to this drill is the fact that when you aren't moving the wheel, depending on what HAL has in mind, HAL may move THS on his own cognizance once you reposition it. This point was also made by some of our Airbus veterans.
Good fun, and no sitting on your hands in an Airbus cockpit!
Consider the Perpignan A320 and how throughly the THS overruled the elevator. Different aircraft, but designed by the same team with similar design philosophy.
Yes it is possible to stall the Bus in ALT2 using just elevator and thrust as we saw demonstrated by AF447, but who can say, had the trim had been limited, whether or not the crew would have seen the airspeed come off the peg a bit during one of their nose down trials and continued their nose down efforts.
THS running full nose up is a potential serious hazard and needs to be guarded against better. How to do that is one for the engineers (design type not wrench type) to puzzle out, but judging from what has recently transpired with the type, it may save two or more aircraft in the future. Expecting training to handle the problem completely is not realistic. If we see nothing in BEA's final accident report addressing this problem, then you should be concerned.
Yes it is possible to stall the Bus in ALT2 using just elevator and thrust as we saw demonstrated by AF447, but who can say, had the trim had been limited, whether or not the crew would have seen the airspeed come off the peg a bit during one of their nose down trials and continued their nose down efforts.
THS running full nose up is a potential serious hazard and needs to be guarded against better. How to do that is one for the engineers (design type not wrench type) to puzzle out, but judging from what has recently transpired with the type, it may save two or more aircraft in the future. Expecting training to handle the problem completely is not realistic. If we see nothing in BEA's final accident report addressing this problem, then you should be concerned.
Some threads ago, one of our Airbus 330 experienced pilots indicated that touching of the trim wheel in some sim training sessions was incentivized against. (Training note: This looks to fall into the realm of something called negative training, as in not correctly incentivizing a proper course of action, or incentiving against a given course of action).
Yet another Airbus 330 experienced poster here, Mikelour IIRC, described some unusual attitude training he encountered where using the trim wheel was one of the best ways to deal with it, though some crews had to be coaxed into using that resource, see above for possible reasons for that.
There seems to be some professional disagreement within the AB community, and the people who train the crews for various companies, on what is and isn't appropriate use of the trim wheels.
I don't think that changes the response to your concern:
if THS runs amok, you can manage it with your hand. What seems to add joy to this drill is the fact that when you aren't moving the wheel, depending on what HAL has in mind, HAL may move THS on his own cognizance once you reposition it. This point was also made by some of our Airbus veterans.
Good fun, and no sitting on your hands in an Airbus cockpit!
I don't know much time you have in tactical jets, but you have enough chutzpah to have come to aviation that way.
The performance of the autotrim system in this corner of the flight envelope likely does not meet certification requirements.
THS running full nose up is a potential serious hazard and needs to be guarded against better.
How to do that is one for the engineers (design type not wrench type) to puzzle out, but judging from what has recently transpired with the type, it may save two or more aircraft in the future.
During this time period the SS was in the average NU, but never full NU
The THS can be limited in movement by using the hand wheel in the cockpit.
There is another method of stopping the nose-up trim: push the stick forward.
Has it something to do with the priority button?
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Clandestino
Quote:
THS running full nose up is a potential serious hazard and needs to be guarded against better.
.
THS running full nose up is a potential serious hazard and needs to be guarded against better.
It did not run away, it was commanded to trim by FC computers.
By the time it got to stop, aeroplane was truly stalled and flight controls were trying to satisfy 2.5G demand which, as we all should know, is impossible to achieve below 1.58 Vs. Demand was given using RH sidestick. Do you dispute that or rather you believe that actual problem is dumb computer obeying supposedly intelligent human which got confused? Do you really want more intelligent computers recognizing when thinking in cockpit has stopped and taking over? IIRC one of the main complaints on PPRuNe was: Airbus computer doesn't let me to do what I want, sob, sob.
Well, on AF447 computers got confused by losing all three speed references so "decided" not to interfere with pilot's demands. That's what is meant by very technical expression "ALT2".
Well, on AF447 computers got confused by losing all three speed references so "decided" not to interfere with pilot's demands. That's what is meant by very technical expression "ALT2".