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737-500 missing in Indonesia

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737-500 missing in Indonesia

Old 12th Nov 2022, 08:39
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@fdr. As pax I found your post refreshingly straightforward. Thank you.
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Old 12th Nov 2022, 15:44
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It's always easy to complain about insufficient URT, though when checking the diagram figures, I don't think, their UR is that bad:
- Within 2 seconds after the AP-off alarm fired, they did have the control wheel back in the position, corresponding to the pre-AP-off position (though that position was already granny compared to what was needed).
- Within subsequent 3 seconds, they were already upside-down in a 360 roll, so, control wheel full to the other side to complete, iso trying to stop the roll.
- Another 3 seconds later, they had wings "somewhat" level.
- Catching the Nr1 still at full throttle AND correcting was 12 seconds after AP-off alarm fired. Late, though given the roll going on and bringing wings somewhat level, let's give them the benefit of the doubt. We should not forget, it's probably not a coordinated roll, so gravity and wild 3D accelerations will throw around people and stuff.
- Looking at the last 1.5 seconds, the Ground speed and Computed Airspeed largely overlap, implying a far from vertical speed-vector, or better, nearly near horizontal.
- Looking at the VS vs. PA, the VS reached nearly 0 at the end, so they nearly made it to horizontal flight, before hitting the water.
- There were 24 seconds between AP-off alarm and hitting the water......

All in all, it's killing they didn't notice the throttle position discrepancy, though the recovery wasn't that bad, I'd say. They just did have the bad luck of just running out of height.

Really shocking, that an AP-off can in just 2 seconds develop into a such an irrecoverable and catastrophic situation.

Not to say, this accident clearly proves, the AP should not "let go" when reaching the end of its control wheel authority, but "freeze" (of course, with alarm), until manually turned off, when the pilots are hands-on. THIS "AP let go" is what caused the Upset to develop (rapidly), not the pilots themselves. Shocking.

Feel free to correct me.
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Old 12th Nov 2022, 17:04
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I think it all goes back to basic trraining. A little upside down time on limited panel instruments goes a long way, and stays with you for a long time - it helps to reduce the 'startle effect' and teaches basic aircraft control. Whether, or how much, these skills should be practised later is a mute point. And I doubt that the UPRT simulator training is sufficient.
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Old 12th Nov 2022, 19:00
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Originally Posted by Bergerie1
I think it all goes back to basic trraining. A little upside down time on limited panel instruments goes a long way, and stays with you for a long time - it helps to reduce the 'startle effect' and teaches basic aircraft control. Whether, or how much, these skills should be practised later is a mute point. And I doubt that the UPRT simulator training is sufficient.
Let me first mention, that I agree with you about the URT at a young age. Where most pilots just hate these upset items, I personally liked these challenging things the most (these trainings being largely outside the normal curriculum).

However, with a B737, we should not forget, this is not a Pitts, Extra, Van, or even a C172. A B737 does have a large (roll-) inertia, implying, once it rolls, it'll take significant forces and time to "undo" that. And, for this case, they had "wings level" (but significant nose down) within some 6-8 seconds after the AP alarm kicked in. Not bad, I'd say, for a large aircraft. So, yeah, they reacted pretty fast (though initially forgetting the throttles).

What killed them, was the lack of height to undo the nose-down situation. IIRC, for AF447, it was calculated, that once they passed down 20K ft, they no longer did have enough height to recover, before splashing (let alone, they lost the plot and did go through 20K ft in a flat, but stable, stall).
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Old 13th Nov 2022, 00:00
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Startle? seriously, if you are jamming your ear into the rail that the DV window slides on, one can assume that anyone with a heartbeat and a modicum of interest in the proceedings would respond with some level of curiosity
fdr, I was going to suggest going back to open cockpits so you could feel the wind on the face, but you've shot me down , the old timers didn't like the introduction of canopies because they and the aircraft were no longer "one". Love your work irrespective of thread.
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Old 13th Nov 2022, 00:10
  #866 (permalink)  
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Originally Posted by WideScreen
It's always easy to complain about insufficient URT, though when checking the diagram figures, I don't think, their UR is that bad:
- Within 2 seconds after the AP-off alarm fired, they did have the control wheel back in the position, corresponding to the pre-AP-off position (though that position was already granny compared to what was needed).
- Within subsequent 3 seconds, they were already upside-down in a 360 roll, so, control wheel full to the other side to complete, iso trying to stop the roll.
- Another 3 seconds later, they had wings "somewhat" level.
- Catching the Nr1 still at full throttle AND correcting was 12 seconds after AP-off alarm fired. Late, though given the roll going on and bringing wings somewhat level, let's give them the benefit of the doubt. We should not forget, it's probably not a coordinated roll, so gravity and wild 3D accelerations will throw around people and stuff.
- Looking at the last 1.5 seconds, the Ground speed and Computed Airspeed largely overlap, implying a far from vertical speed-vector, or better, nearly near horizontal.
- Looking at the VS vs. PA, the VS reached nearly 0 at the end, so they nearly made it to horizontal flight, before hitting the water.
- There were 24 seconds between AP-off alarm and hitting the water......

All in all, it's killing they didn't notice the throttle position discrepancy, though the recovery wasn't that bad, I'd say. They just did have the bad luck of just running out of height.

Really shocking, that an AP-off can in just 2 seconds develop into a such an irrecoverable and catastrophic situation.

Not to say, this accident clearly proves, the AP should not "let go" when reaching the end of its control wheel authority, but "freeze" (of course, with alarm), until manually turned off, when the pilots are hands-on. THIS "AP let go" is what caused the Upset to develop (rapidly), not the pilots themselves. Shocking.

Feel free to correct me.
The crew had asymmetric thrust for approximately 90 seconds, not because an engine had sneakily failed, but because the lever for that engine was not in an eye pleasing location. That places a yaw on the aircraft that the B737 AP can only counter with aileron. The Thrust lever is in the view of a crew that are not asleep. The control column is in view of the crew assuming they aren't doing a crossword puzzle or watching movies on an iPad. The left yaw puts a force on the drivers... pushing the pilot sitting in the left seat (as surely in command is a poor description) head to the right, towards the thrust levers. The co-seat occupier has his right ear being forced towards the #3 window. and there is no interest in the proceedings?

The AP gives up when it gets fed up with the lack of supervision. It cannot and must not freeze in position, it must decouple. Indeed, that gives a removal of the sneaky perfidious autopilots roll countering input, and that results in a rapid roll onset due to the asymmetry that has sat there for... a minute and a half.

A minute and a half, that's about a 5th of a Classic Sudoku, its about 90 seconds of video... at 100m/sec, its 9Km...

Thrust did come off eventually, at VNE. Its supposed to.

The aircraft impacts at around 30 degrees nose down, relatively wings level and about 100 kts faster than VNE. ( the data traces here are lousy scaling of data, the raw data would be interesting, but only from a morbid curiosity POV). At least it was nearly wings level. The crew would not have seen a horizon, apart from it being dark...

Did the crew respond? Lets see, thrust came off at around VNE, and inverted, in a steep dive, with the plane continuing to roll. Aileron inputs were made in both directions and yes, better data would help determine if they actually knew which way was up.

Once wings level, and about 250kts above the trimmed speed... the plane is going to be pitching up due to Static Longitudinal Stability [25.173(b)] so we want to see the control column input or elevator position to determine what the crew were doing, as the plane would be reducing the dive angle naturally anyway.

From reaching 90 degree bank, which should have got some attention, it takes.... ? 8 seconds, 9 seconds? to reach maximum dive angle, and the plane slowly continued the roll through inverted to upright. As said, a half descent barrel roll, other than going down hill, maybe it was a descending scissor. What it isn't is a timely recovery from what should have been obvious for a minute of a half.

I credit the plane with more effective recovery as part of the 25 certification requirements. The crew were not In command of the plane.

If pilots want to dress up in fancy uniforms, I for one would like them to actually care about their profession. When I fly my own jets today, I no longer dress up, after 27,000 hours I am embarrassed to call myself a member of our profession. When asked what I do for a living, I prefer to tell the curious "I am a honky tonk piano player at a brothel..."

This crew at least should have died relaxed. The passengers were probably less so.

The flight path of this was obvious at the time of the event. The precipitating factor was evident about a week later. My frustration is that the data, such that it is, (please get expanded scale of the performance parameters, and add elevator and stab... ) is that it took so long and was so blindingly evident that it was amiss, and the crew snoozed through it all. 90 seconds of SA Type I error... with multiple clues, visual, physical...



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Old 13th Nov 2022, 00:17
  #867 (permalink)  
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Originally Posted by megan
fdr, I was going to suggest going back to open cockpits so you could feel the wind on the face, but you've shot me down , the old timers didn't like the introduction of canopies because they and the aircraft were no longer "one". Love your work irrespective of thread.
stick barbs pointing inwards from the sides of the cockpit, perhaps the crews would notice that all is not well when stuck with a fish hook. or an electric prod...

Apparently being slapped in the side of the head by lateral forces is too subtle for us nowadays.
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Old 13th Nov 2022, 00:36
  #868 (permalink)  
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Originally Posted by WideScreen
However, with a B737, we should not forget, this is not a Pitts, Extra, Van, or even a C172. A B737 does have a large (roll-) inertia, implying, once it rolls, it'll take significant forces and time to "undo" that. And, for this case, they had "wings level" (but significant nose down) within some 6-8 seconds after the AP alarm kicked in. Not bad, I'd say, for a large aircraft. So, yeah, they reacted pretty fast (though initially forgetting the throttles).
Please reconsider your statement on roll inertia. The B737, depending on the version has adequate aileron authority, other than below crossover AOA (it is not speed, please stop calling it speed, the aircraft doesn't care about speed, it only cares about AOA... well, yes, speed for... anyway, crossover is not a speed, it is an AOA).

Once a rapid roll has been initiated, neutralising the roll control input will cease the roll, quite promptly. An opposite roll control input will reduce the time to go to zero roll rate, however the B737 will damp a roll rate in about a second, so at the most optimistic and enthusiastic roll rates, say 40 deg/sec, you get an additional 20 degrees of roll approximately. If you used any opposite input, then the 40 deg/sec rate will be removed almost instantly, coffee will spill in both cases, more in the second.

The B737 ailerons are effective through to stall, and actually below, but with caution, as in most aircraft, large aileron inputs in the stall or above stall AOA can lead to a roll reversal. Spoiler roll control remains effective. Crossover AOA relates to the relative authority of the rudder vs aileron in roll control. At normal speeds, the ailerons are adequate. At high speed, the ailerons respond normally. Above VNE/MMO the ailerons generally act normally, however, at extremely high speed excursions, large aileron inputs can result in roll reversal, that is in the 450KCAS and above range, and at that point it is time to stop playing about. There is a single set of data that shows a roll reversal occurring, and it did not end well, and the whole trainwreck was caused by the Pilot-In-The-Left-Seat-Being-Paid-To-Nominally-Be-In-Command.

Roll rate is determined by control deflection, (aileron/roll spoiler/rudder, AOA, CAS, and speed brake effects on lift distribution. Thrust asymmetry gives a secondary roll... which is what the AP was managing in this case, until it couldn't. Roll rate can also be affected by any mis scheduling of a FBW gain that has erroneous sensor data such as actual flap deflection, Roll damping has additionally density effects. (not the whole answer, it is the bits of interest)


At 07:40:05 UTC:
  • the control wheel trim switch activated and A/P disengaged,
  • the aircraft rolled to the left with the roll angle of about 49,
  • the highest aircraft altitude recorded was about 10,700 feet, thereafter the aircraft continued to descend until the end of FDR recording,
  • the left thrust lever decreased to a position of about 8 and the N1 speed of the left engine was at about 34%,
  • the right thrust lever position and the N1 speed of the right engine remain unchanged, and
  • after the A/P was disengaged, the control wheel was deflected to the left for four seconds and recorded deflection value up to 18.
1:25 after the anomaly, the crew didn't comprehend what had happened. The AP disconnected because the trim switch was actuated. Once that happened, a condition that the AP had about 1/3 RWD input of the ailerons, with the aircraft already rolled to the left "inexplicably", the pilot puts in up to 2/3 LWD aileron for a short period. "BANK ANGLE" GPWS Mode 6 triggered 2 seconds before this....

Last edited by fdr; 13th Nov 2022 at 02:10. Reason: info added
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Old 13th Nov 2022, 06:42
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Originally Posted by WideScreen
Looking at the VS vs. PA, the VS reached nearly 0 at the end, so they nearly made it to horizontal flight, before hitting the water.
Originally Posted by fdr
The aircraft impacts at around 30 degrees nose down
Are we looking at the same graphs here ?
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Old 13th Nov 2022, 08:44
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Originally Posted by fdr
The crew had asymmetric thrust for approximately 90 seconds, not because an engine had sneakily failed, but because the lever for that engine was not in an eye pleasing location. That places a yaw on the aircraft that the B737 AP can only counter with aileron. The Thrust lever is in the view of a crew that are not asleep. The control column is in view of the crew assuming they aren't doing a crossword puzzle or watching movies on an iPad. The left yaw puts a force on the drivers... pushing the pilot sitting in the left seat (as surely in command is a poor description) head to the right, towards the thrust levers. The co-seat occupier has his right ear being forced towards the #3 window. and there is no interest in the proceedings?
Yes, of course, they should have had a better look at the TL.

However, we all know, people aren't that well in monitoring something and concluding that something changed only once in a million (or less). In the old days, yep, there were no alternatives. Nowadays, we have computers for that, just generating an alarm, etc.

Originally Posted by fdr
The AP gives up when it gets fed up with the lack of supervision. It cannot and must not freeze in position, it must decouple. Indeed, that gives a removal of the sneaky perfidious autopilots roll countering input, and that results in a rapid roll onset due to the asymmetry that has sat there for... a minute and a half.
Yep, giving up, returning the aircraft violently to its natural aerodynamic force is old history and should not happen nowadays.

Compare that with "autopilots" in cars (the real and the Tesla-fake-ones), they give a warning to the driver "Please take over, I am going to kick out". It's regulatory.

An aircraft AP should simply do the same.

So, maybe I should rephrase, about the freeze: This should not intended to be a permanent freeze, though maybe 10 seconds or so (with alarm, blablabla), to give the cockpit crew an opportunity to assess and take over, after they have a snap of the situation. I think, this is especially noteworthy, when the out-of-control-authority goes slow (and the subsequent control changes when the AP gives up, can be expected to be major, as was in this case). IF there would have been a freeze for 10 seconds, I don't think, this accident would have happened.

Of course, the B737 in this situation is an old one, though the same mechanisms/limitations do apply to the current B737 (Hence more reasons to declare that airframe obsolete, Jurassic).

And, we should not forget, when the person controlling is not in the center of rotational movements, the forces on that person can be pretty violent. Also, being some 10 meters in front of the aircraft center of gravity, the forces the pilots experience are significant and in all directions/rotation-axis. Think of sitting in the last carriage in a rollercoaster. That's the one with the highest negative and rotational g's, not the front ones ......
Or, cabin crew visiting the rear-galley ceiling, when changing pitch a little too abrupt.

Originally Posted by fdr
A minute and a half, that's about a 5th of a Classic Sudoku, its about 90 seconds of video... at 100m/sec, its 9Km...

Thrust did come off eventually, at VNE. Its supposed to.
See above.

Originally Posted by fdr
The aircraft impacts at around 30 degrees nose down, relatively wings level and about 100 kts faster than VNE. ( the data traces here are lousy scaling of data, the raw data would be interesting, but only from a morbid curiosity POV). At least it was nearly wings level. The crew would not have seen a horizon, apart from it being dark...
We can discuss about the actual speeds, the amount of nose-down, etc, though it is obvious from the diagrams, the VS "decreased" from a staggering -45K/min (seemingly out of scale ?) to less than -5K/min at sea level. Still a lot, though it just signals there was significant recovery, though they ran out of available height.

Originally Posted by fdr
Did the crew respond? Lets see, thrust came off at around VNE, and inverted, in a steep dive, with the plane continuing to roll. Aileron inputs were made in both directions and yes, better data would help determine if they actually knew which way was up.

Once wings level, and about 250kts above the trimmed speed... the plane is going to be pitching up due to Static Longitudinal Stability [25.173(b)] so we want to see the control column input or elevator position to determine what the crew were doing, as the plane would be reducing the dive angle naturally anyway.

From reaching 90 degree bank, which should have got some attention, it takes.... ? 8 seconds, 9 seconds? to reach maximum dive angle, and the plane slowly continued the roll through inverted to upright. As said, a half descent barrel roll, other than going down hill, maybe it was a descending scissor. What it isn't is a timely recovery from what should have been obvious for a minute of a half.

I credit the plane with more effective recovery as part of the 25 certification requirements. The crew were not In command of the plane.
Not in command: Just 2-3 seconds after the AP kicked out, they regained positive control activitity though in just that few seconds, the aircraft was already reached the state, it was doomed to crash, given the lack of height. The unnoticed TL disparity should have been noticed, though it could very well be, they were just "busy" with something else and let us be real, a significant TL disparity was only for around 35 seconds until the AP kicked out. Some years ago, an Eastern Air Lockheed L-1011-1 TriStar did land in the Everglades, just because they all monitored a burned out and they had minutes to conclude the AP kicked out due to a yoke push. And these were all highly experienced US aviators at the top of their performance curve.

Originally Posted by fdr
If pilots want to dress up in fancy uniforms, I for one would like them to actually care about their profession. When I fly my own jets today, I no longer dress up, after 27,000 hours I am embarrassed to call myself a member of our profession. When asked what I do for a living, I prefer to tell the curious "I am a honky tonk piano player at a brothel..."

This crew at least should have died relaxed. The passengers were probably less so.
A bit morbid, though, I think, reality in the nowadays-world is a bit different from when you started your career. Nowadays, there is a huge amount of "regulations" (not only to "know" these, though also how to handle accordingly), that much that the factual technical flying aspects as you learned initially, get snowed under. The regulations is something, you gradually learned during your career. Current pilots need to learn both the tech flying items, as well as the regulations, all at the beginning of their career. As laid out in another PP thread, people can only learn a limited amount in a set time, so, yeah, things to learn will be falling off the learning table, just choose.

Then we not yet spoke about the regulatory environment, when these pilots started their career. I won't call it cowboy (buffalo for those areas of the globe), though it is likely, that it was quite far behind Western (Post Tenerife) learning environments in those days. Developing countries, etc. Glossy phones tend to be more important than to assert daily food is available.

Oh, and, I don't think, they were inverted when the trust came off. The inverted aspect seemed to be "solved" within 7-8 seconds.

Originally Posted by fdr
The flight path of this was obvious at the time of the event. The precipitating factor was evident about a week later. My frustration is that the data, such that it is, (please get expanded scale of the performance parameters, and add elevator and stab... ) is that it took so long and was so blindingly evident that it was amiss, and the crew snoozed through it all. 90 seconds of SA Type I error... with multiple clues, visual, physical...

Yep, it's frustrating how things went, though the technology giving up without warnings and the fact that in just 2-3 seconds things developed unrecoverable/doomed when a human fails to notice something seldom happening, should give people the thinking: "Hmmmm, this should be done different".

And, no, I am not from a "younger" generation, know everything better, though roughly your age, with significant experience in other areas, though realistic enough to conclude that old-style methods simply don't work any longer. IF you want to improve safety, it's not around "more regulations/procedures", though have a realistic look at the human limitations and mitigate on this. An AP kicking out, returning an aircraft violently to it aerodynamic forces, is a mechanism waiting for disaster, as this case showed. TL's moving into disparity without "warning" is a mechanism waiting for disaster, as this case showed.
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Old 13th Nov 2022, 09:58
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Originally Posted by fdr
Please reconsider your statement on roll inertia. The B737, depending on the version has adequate aileron authority, other than below crossover AOA (it is not speed, please stop calling it speed, the aircraft doesn't care about speed, it only cares about AOA... well, yes, speed for... anyway, crossover is not a speed, it is an AOA).
Not sure where the speed comes from.

Originally Posted by fdr
Once a rapid roll has been initiated, neutralising the roll control input will cease the roll, quite promptly. An opposite roll control input will reduce the time to go to zero roll rate, however the B737 will damp a roll rate in about a second, so at the most optimistic and enthusiastic roll rates, say 40 deg/sec, you get an additional 20 degrees of roll approximately. If you used any opposite input, then the 40 deg/sec rate will be removed almost instantly, coffee will spill in both cases, more in the second.

The B737 ailerons are effective through to stall, and actually below, but with caution, as in most aircraft, large aileron inputs in the stall or above stall AOA can lead to a roll reversal. Spoiler roll control remains effective. Crossover AOA relates to the relative authority of the rudder vs aileron in roll control. At normal speeds, the ailerons are adequate. At high speed, the ailerons respond normally. Above VNE/MMO the ailerons generally act normally, however, at extremely high speed excursions, large aileron inputs can result in roll reversal, that is in the 450KCAS and above range, and at that point it is time to stop playing about. There is a single set of data that shows a roll reversal occurring, and it did not end well, and the whole trainwreck was caused by the Pilot-In-The-Left-Seat-Being-Paid-To-Nominally-Be-In-Command.

Roll rate is determined by control deflection, (aileron/roll spoiler/rudder, AOA, CAS, and speed brake effects on lift distribution. Thrust asymmetry gives a secondary roll... which is what the AP was managing in this case, until it couldn't. Roll rate can also be affected by any mis scheduling of a FBW gain that has erroneous sensor data such as actual flap deflection, Roll damping has additionally density effects. (not the whole answer, it is the bits of interest)
Of course, the B737 does have sufficient aileron authority. That's not the issue.

Though, when you have a large aircraft (roughly 3 times the wingspan of a small aerobatic frame), your inertia forces will increase significantly, because the forces/energy are with roll-rate^2 (IE tip-roll-speed).

Aerobatic aircraft tend to have 180+ degrees/second roll-rates. A B737 doesn't do that (the report states 49 degrees/second) and IF you could try 180+ degrees/second, you'll rip off the control surfaces, the engines (Gyroscopic effects), the wings, etc. There was a nice article on PP, about B707's crashing (presumably after barrel roll attempts), and/or engines departing the frame. When the rotating engine core is not perfectly aligned with the roll axis, but wobbles around that, and with 4 engines also circles around the roll axis, the gyroscopic forces on the engines are enormous. Enough to tear-off the whole engine, which happened.

With 49 degrees/second, you get 3.5 seconds to inverted and probably another 3.5 seconds to get blue up again. Which nicely matches, with my earlier graphic reading.

Of course, when you approach the perfect blue-up situation, it's tricky to have the roll stop at that moment, so the roll somewhat oscillated around the desired position, so be it.

Originally Posted by fdr
At 07:40:05 UTC:
  • the control wheel trim switch activated and A/P disengaged,
  • the aircraft rolled to the left with the roll angle of about 49,
  • the highest aircraft altitude recorded was about 10,700 feet, thereafter the aircraft continued to descend until the end of FDR recording,
  • the left thrust lever decreased to a position of about 8 and the N1 speed of the left engine was at about 34%,
  • the right thrust lever position and the N1 speed of the right engine remain unchanged, and
  • after the A/P was disengaged, the control wheel was deflected to the left for four seconds and recorded deflection value up to 18.
1:25 after the anomaly, the crew didn't comprehend what had happened. The AP disconnected because the trim switch was actuated. Once that happened, a condition that the AP had about 1/3 RWD input of the ailerons, with the aircraft already rolled to the left "inexplicably", the pilot puts in up to 2/3 LWD aileron for a short period. "BANK ANGLE" GPWS Mode 6 triggered 2 seconds before this....
With the control wheel obviously significantly out of neutral, it is strange, they did input only a short trim-blip. Given the violent control wheel movement after the short blip, it suggests, the control wheel wasn't really in firm hands. Strange and gives me the impression, the trim-blip was unintentionally. It could very well be, the trim-blip did happen due to the control wheel acceleration or just the movement and touching something. The fact that the AP kicks out just at the same moment of a trim-blip, does not imply a cause-action, it could have happened simultaneously, with an opposite cause-action as normal logic determines. The graphic time-line resolution seems to be "only" around 1.5 seconds.

Not to say, I can't imagine a pilot doing a one-finger trim-switch push and not having the significantly out of neutral control wheel firmly in his/her hands. Not to say, the way the pilot reacted to the roll (not "fighting" the roll, but helping to roll through the upside down position towards blue-up) and realized wings-level that fast, implies a lot of flying experience, a pilot with military / fighter-yet experience ?

The control wheel deflected to the left for 4 seconds is understandable. If you want to get your blue up as fast as possible, you are going to help the continued rotation, the moment, you are already at or approaching 100% upside down. When looking at that trace, I don't see things which do surprise me, on the contrary, they pretty well understood what was happening AND what to do about it (continue the roll and stop "around" blue-up).

Unfortunately, they ran out of height to finish the recovery.
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Old 13th Nov 2022, 13:31
  #872 (permalink)  
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Originally Posted by WideScreen
Not sure where the speed comes from.


Of course, the B737 does have sufficient aileron authority. That's not the issue.

Though, when you have a large aircraft (roughly 3 times the wingspan of a small aerobatic frame), your inertia forces will increase significantly, because the forces/energy are with roll-rate^2 (IE tip-roll-speed).

Aerobatic aircraft tend to have 180+ degrees/second roll-rates. A B737 doesn't do that (the report states 49 degrees/second) and IF you could try 180+ degrees/second, you'll rip off the control surfaces, the engines (Gyroscopic effects), the wings, etc. There was a nice article on PP, about B707's crashing (presumably after barrel roll attempts), and/or engines departing the frame. When the rotating engine core is not perfectly aligned with the roll axis, but wobbles around that, and with 4 engines also circles around the roll axis, the gyroscopic forces on the engines are enormous. Enough to tear-off the whole engine, which happened.

With 49 degrees/second, you get 3.5 seconds to inverted and probably another 3.5 seconds to get blue up again. Which nicely matches, with my earlier graphic reading.

Of course, when you approach the perfect blue-up situation, it's tricky to have the roll stop at that moment, so the roll somewhat oscillated around the desired position, so be it.


With the control wheel obviously significantly out of neutral, it is strange, they did input only a short trim-blip. Given the violent control wheel movement after the short blip, it suggests, the control wheel wasn't really in firm hands. Strange and gives me the impression, the trim-blip was unintentionally. It could very well be, the trim-blip did happen due to the control wheel acceleration or just the movement and touching something. The fact that the AP kicks out just at the same moment of a trim-blip, does not imply a cause-action, it could have happened simultaneously, with an opposite cause-action as normal logic determines. The graphic time-line resolution seems to be "only" around 1.5 seconds.

Not to say, I can't imagine a pilot doing a one-finger trim-switch push and not having the significantly out of neutral control wheel firmly in his/her hands. Not to say, the way the pilot reacted to the roll (not "fighting" the roll, but helping to roll through the upside down position towards blue-up) and realized wings-level that fast, implies a lot of flying experience, a pilot with military / fighter-yet experience ?

The control wheel deflected to the left for 4 seconds is understandable. If you want to get your blue up as fast as possible, you are going to help the continued rotation, the moment, you are already at or approaching 100% upside down. When looking at that trace, I don't see things which do surprise me, on the contrary, they pretty well understood what was happening AND what to do about it (continue the roll and stop "around" blue-up).

Unfortunately, they ran out of height to finish the recovery.

When considering the data, which is a pretty unfortunate scale of the points of interest, note that the last periods are post impact, the aircraft hits the ocean still at a high speed and steep nose down attitude. Post impact there is artefacts of the data. Getting to 450Kts +, 80 AND at ~6000' doesn't get recoverable with the wings intact on a Part 25 transport. It is still ugly if you could pull 7.3g, it might be OK at 9g...



Altitude loss for varying Nz, entry at M=0.80






It is painfully frequent that a pilot intervening with the AP when there is a considerable deflection applied by the AP will far too frequently result in the control position being returned to neutral by air loads. The controls are "irreversible" to an extent, that being that ailerons will return to center when the displacement force is removed. As will the rudder, and the elevator, to a trimmed position.

The B737 design age is not relevant to this situation, other than it has mechanical lever motion to provide and feedback from the engine FCU (+EEC). It is similar to the B777 as far as the AP goes, if the AP has put in half deflection of the aileron and the AP disconnects, the control will revert to neutral rapidly. If the AP was counteracting an force such as yaw/roll couple, then the effect will be impressive.

Had an idiot do that in a B744 once. The wonder examiner added full rudder to the aircraft with the AP disengaged and the engines at idle. The youngster that being "taught a lesson" while hand flying, finally got confused that the near full left aileron was not stopping a trend to roll right, and eventually gave up, the reverse case of the AP disconnecting. The resultant roll rate was spectacular. I walked into the mess to find out why grandma in 99Z had her nose planted on the side window of the plane, just in time to see the world go wild. Aircraft got an inspection for over-stress. Refused to have the examiner ever in the cockpit again. The B747, B744, B757, 767 777 787 will all behave the same as the B737 with an AP disconnect with a deflection of the control by the AP. There are cautions to that effect in all Boeing FCTMs IIRC.

The rock n roll was not that much different here to the wild ride of the B74SP going to California from East Asia.

Last edited by fdr; 13th Nov 2022 at 13:53.
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