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.
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.
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.
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.
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.
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.
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.