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Old 03-26-2019, 08:25 PM   #301
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That's what it said, but it's yet another emergency on takeoff, which will only further reduce confidence in the planes. Especially if it is a different problem entirely, since Boeing then can't claim the upcoming software patch fixed everything. They'd be better off if it was the same issue, ironically.
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Old 03-27-2019, 08:22 AM   #302
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Boeing test pilots and engineers have determined in simulations of the Lion Air crash an unrecoverable dive leading to a crash would have occurred if the MCAS was not shut down within 40s of an AoA data error.

Basically an undisclosed system, which was put in place to save airlines the cost of retraining pilots, had a single point of failure which can kill an untrained flight crew in under a minute. A trained flight crew would have no problems disabling the system. Saving training costs for the airlines cost 300+ people their lives.

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In testing performed in a simulator, Boeing test pilots recreated the conditions aboard Lion Air Flight 610 when it went down in the Java Sea in October, killing 189 people. The tests showed that the crew of the 737 MAX 8 would have only had 40 seconds to respond to the Maneuvering Characteristics Augmentation System’s (MCAS’s) attempts to correct a stall that wasn’t happening before the aircraft went into an unrecoverable dive, according to a report by The New York Times.

While the test pilots were able to correct the issue with the flip of three switches, their training on the systems far exceeded that of the Lion Air crew—and that of the similarly doomed Ethiopian Airlines Flight 302, which crashed earlier this month. The Lion Air crew was heard on cockpit voice recorders checking flight manuals in an attempt to diagnose what was going on moments before they died.

One of the controls—the electric stabilizer trim thumbswitch on the pilot’s control yoke—could temporarily reset MCAS’ control over stabilizers. The Lion Air pilots hit this switch more than 24 times, buying them some time—but MCAS’ stall prevention software kicked in afterwards each time because of faulty data coming from the aircraft’s primary angle of attack sensor.

Completely disabling MCAS’ control over the aircraft’s stabilizers would be the only way to overcome that sensor failure in the current software version. That requires throwing two additional switches on the console and turning a trim wheel on the console manually to re-establish manual control.

The Lion Air crew would have had to accomplish this while dealing with a host of alerts, including differences in other sensor data between the pilot and co-pilot positions that made it unclear what the aircraft’s altitude was. As a result, the crew continued to fight MCAS’ attempts to push the nose down until the end.
https://arstechnica.com/information-...vent-disaster/

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Old 03-27-2019, 10:53 AM   #303
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Keep in mind, that 40 seconds was if they did nothing to try to counteract it. The Captain in in the Lion air accident flew for several minutes because he was continually trimming against it. It was only when he switched control and the other pilot was not countering the system that they finally lost control.

Not that I’m defending the system, but the 40 second number is like saying if you don’t try to keep you car in the middle of the road you will crash in less than a minute.
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Old 03-27-2019, 11:29 AM   #304
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Originally Posted by Ryan Coke View Post
Keep in mind, that 40 seconds was if they did nothing to try to counteract it. The Captain in in the Lion air accident flew for several minutes because he was continually trimming against it. It was only when he switched control and the other pilot was not countering the system that they finally lost control.

Not that I’m defending the system, but the 40 second number is like saying if you don’t try to keep you car in the middle of the road you will crash in less than a minute.
Yes, the New York Times article that was also linked in here mentioned that they essentially reset it multiple times by trying to use the thumb trim switch.

Sad situation.
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Old 03-27-2019, 11:30 AM   #305
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Originally Posted by FlameOn View Post
Boeing test pilots and engineers have determined in simulations of the Lion Air crash an unrecoverable dive leading to a crash would have occurred if the MCAS was not shut down within 40s of an AoA data error.

Basically an undisclosed system, which was put in place to save airlines the cost of retraining pilots, had a single point of failure which can kill an untrained flight crew in under a minute. A trained flight crew would have no problems disabling the system. Saving training costs for the airlines cost 300+ people their lives.



https://arstechnica.com/information-...vent-disaster/
40 seconds...in the hands of Boeing test pilots knowing to expect an error who would be able to react within those 40 seconds.

In other words, a well trained crew knowing about the MCAS and testing for the scenario would have had 40 seconds or less to disable the problem after noticing it, versus a crew that had no idea the system even existed because it was not disclosed or trained on. Boeing built a system that actively was trying to crash a fricking plane if not countered within 40 seconds, and decided not to tell anyone about it to save on cost.

A pilot taking a sip of coffee and a few seconds of inattention on a 6 hour flight could be enough to cause a plane to crash. And you have to remember to turn off 3 specific switches, after identifying the problem, within the seconds you have left or you die.

And this is the Lion Air situation, we still don't know all the details of the Ethopian Air crash, where the pilots did know about MCAS at that point. That 40 seconds for Lion Air may have been 15 seconds for Ethiopian Air due to different conditions. It crashed much sooner than Lion Air.

Lion Air pilots hit the switch over 24 times while scrambling through the manual until they eventually lost control (and they would have no idea of a 40 second counter of course).

This is like pressing the button from Lost, Boeing edition
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Old 03-27-2019, 02:39 PM   #306
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40 seconds...in the hands of Boeing test pilots knowing to expect an error who would be able to react within those 40 seconds.

In other words, a well trained crew knowing about the MCAS and testing for the scenario would have had 40 seconds or less to disable the problem after noticing it, versus a crew that had no idea the system even existed because it was not disclosed or trained on. Boeing built a system that actively was trying to crash a fricking plane if not countered within 40 seconds, and decided not to tell anyone about it to save on cost.

A pilot taking a sip of coffee and a few seconds of inattention on a 6 hour flight could be enough to cause a plane to crash. And you have to remember to turn off 3 specific switches, after identifying the problem, within the seconds you have left or you die.

And this is the Lion Air situation, we still don't know all the details of the Ethopian Air crash, where the pilots did know about MCAS at that point. That 40 seconds for Lion Air may have been 15 seconds for Ethiopian Air due to different conditions. It crashed much sooner than Lion Air.

Lion Air pilots hit the switch over 24 times while scrambling through the manual until they eventually lost control (and they would have no idea of a 40 second counter of course).

This is like pressing the button from Lost, Boeing edition
Dramatic much? Did you know there is a simple memory procedure for runaway trim which the Lion Air crew did not wholly execute? They only had to utilize the trim cut-off switches, it appears they did not. In fact, the procedure for runaway trim is pretty much the same for all Boeing airframes since the 707 debuted, including the military heavies. Had the crew followed proper procedure for a runaway trim situation, this crash likely wouldn’t have occurred. If the crew knew nothing of MCAS, than why did they not follow procedure for runaway trim when their aircraft continually went nose down uncommanded? Previous Lion Air crews were able to rectify the same situation on the same hull that crashed, this crew did not. Let’s not forget the MCAS system was doing its job based on the erroneous AoA data, Lion Air maintenance had already replaced the AoA indicator which was serving the incorrect data. If the problem persisted with the indicator, this aircraft should have not been airworthy.

Regardless of MCAS being involved, the procedure for runaway trim does not change.
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Old 03-27-2019, 04:34 PM   #307
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Dramatic much? Did you know there is a simple memory procedure for runaway trim which the Lion Air crew did not wholly execute? They only had to utilize the trim cut-off switches, it appears they did not. In fact, the procedure for runaway trim is pretty much the same for all Boeing airframes since the 707 debuted, including the military heavies. Had the crew followed proper procedure for a runaway trim situation, this crash likely wouldn’t have occurred. If the crew knew nothing of MCAS, than why did they not follow procedure for runaway trim when their aircraft continually went nose down uncommanded? Previous Lion Air crews were able to rectify the same situation on the same hull that crashed, this crew did not. Let’s not forget the MCAS system was doing its job based on the erroneous AoA data, Lion Air maintenance had already replaced the AoA indicator which was serving the incorrect data. If the problem persisted with the indicator, this aircraft should have not been airworthy.

Regardless of MCAS being involved, the procedure for runaway trim does not change.
I guess one question would be - is a MCAS malfunction easily identifiable as a case of runaway trim? Certainly the one Lion Air crew successfully identified that (well technically, it has been reported that it was an off-duty pilot who identified the correct solution). My understanding is that the MCAS would activate intermittently - does that make it different than other runaway trim scenarios that the pilots should definitely have been trained to identify?
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Old 03-27-2019, 04:56 PM   #308
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I'm not sure why it would matter, and I don't know that a pilot needs to identify the failing system, just the procedure to address it. The procedure for runaway trim looks to be the same, no matter the cause.


While a failing sensor shouldn't default to auto-crash mode(and Boeing is really not looking good on this one), this, in my view, is something any pilot should have been able to sort out fairly quickly. There is a good reason to have 2 trained pilots on the flight deck, not 1 trained pilot and a 200 hour trainee.
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Old 03-27-2019, 05:09 PM   #309
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I guess one question would be - is a MCAS malfunction easily identifiable as a case of runaway trim? Certainly the one Lion Air crew successfully identified that (well technically, it has been reported that it was an off-duty pilot who identified the correct solution). My understanding is that the MCAS would activate intermittently - does that make it different than other runaway trim scenarios that the pilots should definitely have been trained to identify?

Runaway trim is runaway trim, you deal with it the same way. If your aircraft is pitching up or down without pilot input, there is likely a trim issue, address it as such and figure out the cause after the fact once the aircraft is under control. Boeing designed the MCAS system to be a 'blind' safety mechanism to prevent an imminent aerodynamic stall, hence the reason most knew little about it. It is supposed to be the proverbial 'safety blanket' to prevent the wings from stalling at high angles of attack. Unfortunately, Boeing did not seemingly design the system as good as it should have been with more redundancies and comparative data.

There is no replacement for experience and proper training in the aviation world, be it pilot/AME or ATC. Based on what has already been reported, the Lion Air crash appears to have been preventable regardless of the faults that correlate back to the bad AoA data and MCAS system (unless something else comes to light).

Acey made some great comments in a previous post regarding pilot skill/knowledge - notably mentioning the Asiana crash in San Francisco which really highlighted the human factor in aircraft accidents.

Regardless of the final findings from both MAX crashes, pilot experience/training are most surely to be mentioned alongside the other factual information found.
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Old 03-27-2019, 05:33 PM   #310
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Runaway trim is runaway trim, you deal with it the same way. If your aircraft is pitching up or down without pilot input, there is likely a trim issue, address it as such and figure out the cause after the fact once the aircraft is under control. Boeing designed the MCAS system to be a 'blind' safety mechanism to prevent an imminent aerodynamic stall, hence the reason most knew little about it. It is supposed to be the proverbial 'safety blanket' to prevent the wings from stalling at high angles of attack. Unfortunately, Boeing did not seemingly design the system as good as it should have been with more redundancies and comparative data.

There is no replacement for experience and proper training in the aviation world, be it pilot/AME or ATC. Based on what has already been reported, the Lion Air crash appears to have been preventable regardless of the faults that correlate back to the bad AoA data and MCAS system (unless something else comes to light).

Acey made some great comments in a previous post regarding pilot skill/knowledge - notably mentioning the Asiana crash in San Francisco which really highlighted the human factor in aircraft accidents.

Regardless of the final findings from both MAX crashes, pilot experience/training are most surely to be mentioned alongside the other factual information found.
Thanks, that's helpful - I don't know anything about flying so I'm just going by what I read. If it's as simple as aircraft pitching without pilot input --> possible trim issue --> execute runaway trim procedure, then it does seem like a procedural breakdown is the biggest culprit - my question was moreso if it was possible that the pilots didn't recognize this as being a trim issue at all, not if they could identify the cause.
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Old 03-27-2019, 05:53 PM   #311
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I would say that while I agree with Flame Envy overall, your question is a good one. I would have thought that an MCAS fault would’ve been readily identified as some sort of a trim runaway issue, but if 2 crews had problems with that diagnosis, it does make me wonder if it is not as obvious as I would have expected.
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Old 03-27-2019, 07:13 PM   #312
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Even if the breakdown was procedural failure you have to understand that when people perform a task that procedures will sometimes fail no matter how well trained the individuals are. So the design of the plane needs to mitigate the consequences of human error. Ironically the MCAS system was designed to do that for a different issue.
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Old 03-28-2019, 08:42 AM   #313
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Dramatic much? Did you know there is a simple memory procedure for runaway trim which the Lion Air crew did not wholly execute? They only had to utilize the trim cut-off switches, it appears they did not. In fact, the procedure for runaway trim is pretty much the same for all Boeing airframes since the 707 debuted, including the military heavies. Had the crew followed proper procedure for a runaway trim situation, this crash likely wouldn’t have occurred. If the crew knew nothing of MCAS, than why did they not follow procedure for runaway trim when their aircraft continually went nose down uncommanded? Previous Lion Air crews were able to rectify the same situation on the same hull that crashed, this crew did not. Let’s not forget the MCAS system was doing its job based on the erroneous AoA data, Lion Air maintenance had already replaced the AoA indicator which was serving the incorrect data. If the problem persisted with the indicator, this aircraft should have not been airworthy.

Regardless of MCAS being involved, the procedure for runaway trim does not change.
Would that, by chance, be related to this snippet from the Ars Technica article?

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One of the controls—the electric stabilizer trim thumbswitch on the pilot’s control yoke—could temporarily reset MCAS’ control over stabilizers. The Lion Air pilots hit this switch more than 24 times, buying them some time—but MCAS’ stall prevention software kicked in afterwards each time because of faulty data coming from the aircraft’s primary angle of attack sensor.
Is there a chance that they were trying what you suggest, but that the software kept overriding back into a 'crash me' state, for which they did not know how to disable?
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Old 03-28-2019, 11:15 AM   #314
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Would that, by chance, be related to this snippet from the Ars Technica article?



Is there a chance that they were trying what you suggest, but that the software kept overriding back into a 'crash me' state, for which they did not know how to disable?
Possibly. Very doubtful however based on previous crews on the same hull being able to disable MCAS by employing the STAB cut-off switches during previous flights. The doomed crew apparently did not touch the cut-off switches. The pilots just used the electric trim toggle on the yoke which temporarily disables MCAS, the cut-off switches kills it.


Here is a good AOPA article on the subject. The STAB cut-off switches which are pictured need to be switched off in a runaway trim situation. As I stated earlier, runaway trim is runaway trim regardless of the cause. Follow the memory procedure for runaway trim which includes enabling the cut-off switches.

https://www.aopa.org/news-and-media/...-737-max-fleet
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Old 03-28-2019, 11:19 AM   #315
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Is there a chance that they were trying what you suggest, but that the software kept overriding back into a 'crash me' state, for which they did not know how to disable?
I'm going to link an article that explains MCAS in detail (it's been posted in this thread a couple times), and the spoiler boxes below have the two images from that article that will help illustrate my explanation.

Generally, the purpose of stabilizer trim is to help the pilot so he doesn't have to exert constant heavy pressure on the yoke. Both pilots have thumb switches on the yoke (see first spoiler box) that controls the stabilizer trim.

When the pilot presses that switch, the black electric trim wheel spins, making loud noises, and the stabilizer tilts in the direction the pilot wants it to, until he/she lets go of the switch. This is the switch the Captain of the Lion Air flight was pressing; pilots will adjust stabilizer trim quite often in normal flight.

MCAS trims the stabilizer automatically, and the electric trim wheel spins in the same way as if the pilot was commanding trim up/down motion.

When MCAS is trimming the stabilizer, it will temporarily disengage when the pilot presses the thumb switch on the yoke, and once the pilot lets go, it will re-engage after a few seconds. (see article + second spoiler box)

When you flick the trim cutoff switches (see first spoiler box), that disables the electric motion of the stabilizer trim, and hence, disables both MCAS and the pilot's thumb switch. When you disable automated trim, you have to crank the wheel by hand to adjust the trim, regardless of whether you're flying a 737-800, or a 737 MAX.

So on the Lion Air flight, the Captain knew there was something wrong with the stabilizer trim, because he kept counteracting the trim motion commanded by MCAS. When he handed over control of the plane to the First Officer so he could look through the emergency checklists, the F/O did not make the same trim commands. Whether the Captain told him to or not, we don't know.

But the Captain was obviously on the right track...it baffles me as to why he didn't think to disable the automated trim. If he kept trimming the nose up, he must have known something was constantly trimming it downwards. Whether you know about MCAS or not (or even the fact you're flying a MAX) is irrelevant, like FLAME ENVY said. Any trained/experienced pilot "should" (or so we think) catch onto the fact that "hey, I have a trim problem".

But it's easy for me to say that sitting in my office chair; in an emergency situation where you have NO idea what the plane is doing, your mind is moving a million miles an hour, and it can be easy to miss certain things that one would think should be basic.

None of us (licensed pilots and armchair experts alike) were up there in that situation, so it's impossible to know what was going on in the minds of the crew. And like Ryan Coke said, if two air crews were not able to diagnose this as a trim problem, it begs the question whether the MCAS problem is as obvious as we think.

----

Spoiler!


Spoiler!


https://theaircurrent.com/aviation-s...em-mcas-jt610/

Last edited by Stealth22; 03-28-2019 at 11:40 AM.
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Old 03-28-2019, 02:38 PM   #316
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Could a pilot have indefinitely kept manually compensating against the MCAS with the pilot thumb switch, or does the MCAS progressively increase in magnitude to eventually overwhelm the thumb switch?

Even so that would been extremely annoying and would probably make for a hellish landing.
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Old 03-28-2019, 03:24 PM   #317
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No, MCAS, to my knowledge, won't "overwhelm" the pilot like that, but I'm not a pilot or engineer, so don't quote me on that. There have been articles recently saying that Boeing is tweaking MCAS so it will not continuously try to override the pilot.

MCAS would only keep trying to trim down if the sensor kept feeding it bad AOA data, and the software update is also 1) Ensuring it checks both AOA sensors, and 2) Not taking action if there's a disagreement between the two sensors.

Nevertheless, landing in those conditions would be annoying, but eventually, like we discussed, the pilot should catch on and disable the automated trim.

Why they didn't? If anyone, only the investigators know, at this point.
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Old 03-28-2019, 03:42 PM   #318
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I think the issue is until the trim is manually disabled, the thumb switch only temporarily disables the MCAS trim action. So for Lion Air, it kept triggering on, and they fought it, and then disabled it. From what I gather it only because fatal when the FO took over and wasn't as quick to disable/fight it.

Sounds like the update will permanently disable MCAS when triggered rather than just being a temporary shutoff.
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Old 03-28-2019, 04:16 PM   #319
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I think the issue is until the trim is manually disabled, the thumb switch only temporarily disables the MCAS trim action. So for Lion Air, it kept triggering on, and they fought it, and then disabled it. From what I gather it only because fatal when the FO took over and wasn't as quick to disable/fight it.

Sounds like the update will permanently disable MCAS when triggered rather than just being a temporary shutoff.
Yup, that's exactly what the issue was in the case of Lion Air, or at least, that's the working theory on this page. :P

Maybe it's easy for me to say this given how much I've read about this, but I just don't understand how the Captain sat there for several minutes fighting the trim movements, and never once thought to cut off the electric trim.
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Old 03-28-2019, 04:26 PM   #320
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Yup, that's exactly what the issue was in the case of Lion Air, or at least, that's the working theory on this page. :P

Maybe it's easy for me to say this given how much I've read about this, but I just don't understand how the Captain sat there for several minutes fighting the trim movements, and never once thought to cut off the electric trim.
Came across this post on another forum that helps provide some insight.

Quote:
As a long-time 737 driver I'll just chime-in a few points. Regarding the trim wheel ability to move the stab at high speed from full deflection: I seriously doubt that there would ever be too much force on the elevator that the trim wheel could not move it. There is a lot of leverage in the jack screw, and the turns of the trim wheel make very minute changes to the angle of the stab.

But know that moving from full deflection to neutral would take a painfully long time. On the -200 we used to wind the trim full fore and aft as part of the preflight checks. (We stopped doing that on the NG.) . Using the motor-driven trim this took about a minute to go full forward, full aft, then back to about 4 units. It is not physically possible to wind the trim wheel that fast for that long manually, especially when your aircraft is lurching about like a rodeo bull. Also note that it doesn't take much movement to change the aircraft's attitude significantly, and the aircraft is very controllable using manual trim. Back in the cargo days I once did a 20 minute flight using only the rudder and stab trim and manual power (on the -200) from after flaps up to 10000' on descent. That's right - I didn't touch the yoke, autopilot-off from climb-out to descent. It was very controllable and stable. (That was a good training exercise, too.)

My First Point: If we don't catch this mis-trim early, un-doing it manually will take a very long time and maybe more time than is available when your aircraft is only 1000' AGL. AND to use the trim wheel for more than small changes, one has to fold the handle out. A handle that has injured many a knee in simulator sessions because combined with the trim motor's speedy rotation of the wheel, it can leave one with a permanent limp.

Second: For all the arm-chair Monday morning QB's who are saying: "Oh, they should have recognized it immediately and disconnected the trim:"

(1) Just after takeoff there is a lot going on with trim, power, configuration changes, and as noted above, the darn speed trim is always moving that trim wheel in seemingly random directions to the point that experienced NG pilots would treat its movement as background noise and normal ops. Movement of the trim wheel in awkward amounts and directions would not immediately trigger a memory item response of disconnecting the servos. No way.

(2) The pilots could very reasonably not have noticed the stab trim movement. Movement of the stab trim on the 737 is indicated by very loud clacking as the wheel rotates. On the -200 it was almost shockingly loud. On the NG, much less so. HOWEVER, the 737 cockpit is NOISY. It's one reason I am happy to not be flying it any more. The ergonomics are ridiculous. Especially at high speeds at low altitudes. With the wind noise, they may not have heard the trim wheel moving. The only other way to know it was moving would be yoke feel and to actually look at the trim setting on the center pedestal, which requires looking down and away from the windows and the instruments in a 'leans'-inducing head move. On the 717, for example, Ms. Douglas chimes in with an audible "Stablizer Motion" warning. There is no such indication on the 737.

(3) The fact that they were at high power and high speed tells me the stick shaker was activated. With that massive vibrator between your legs, alternating blue sky and brown out the window, your eye balls bouncing up and down in their sockets as the plane lurches up and down in positive and negative G's, it would have been a miracle if one of the pilots calmly reached down, flicked off the stab servo cutout switches, folded out the trim handle, and started grinding the wheel in the direction of normalcy. These pilots said over the radio that they had "unreliable airspeed". So they did not even know which instruments to rest their eyes on for reliable info. Their eyes were all over the cockpit looking for reliable info, the plane is all over the place like a wild boar in a blanket not behaving in any rational way. And the flying pilot may have been using the tiny standby IFDS for airspeed and attitude. Ouch.

Finally, runaway stab trim is a very, very rare occurence up until now. We trained it about once every other year in the sim because it is so rare. And when we did it was obvious. The nose was getting steadily heavier or steadily lighter with continuous movement of the trim wheel. That is a VERY different scenario than what these pilots faced.

We also trained for jammed stabilizer, the remedy for which is overcoming it with force. The information they were faced with could very reasonably have been interpreted that way, too.

An URGENT AD from the FAA/ Boeing after Lion Air would have helped get it back to the front of the pilot's minds for sure. Extra training by the airline or an urgent pilot memo would have helped. Maybe one was issued, we don't know yet.

A better question might be: given this nose down attitude, high speed, and fully nose down or almost fully nose down stab, how much altitude would they have had to have to be able to recover. I'm thinking at least 10000 feet to recognize the problem, disconnect the switches, fold out the handle and start frantically winding the stab back to normalcy while the flying pilot tries to gain control via the elevator. It's entirely possible that this scenario, if not recognized early on, is unrecoverable at any altitude.
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