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Downfall, Netflix documentary

Old 23rd Feb 2022, 09:51
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the show did not question why the pilots didn't reduce the throttle while in a steep descent with excess airspeed
At the risk of digressing from LB’s post, which raises some very valid points about the documentary:

Reducing the throttle while in a steep descent with excess airspeed would not have solved the airspeed problem, and therefore would not have solved the manual trim problem.

In fact, the only way to save that aircraft at that point in time would be a rapid aileron roll to inverted flight, and if the subsequent negative G inverted pushover manages to avoid ground contact, the airspeed would wash off to the point that manual aft trim would be possible, and a subsequent roll to normal flight, which would have to be accomplished prior to the rapidly impending inverted stall.

Denzel Washington could have told us that, but it usually takes a fair amount of alcohol and cocaine in your system to come up with such an outside-the-square solution…
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Old 23rd Feb 2022, 09:52
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A bit similar (if not all that closely related) to the standard TP approach - if you just did something and something unpleasant happens, undo that which you just did and see if the two might have been related.
In case it might have been missed, the pilots were not test pilots, they were line pilots. No manufacturer should release a design to service that requires anything approaching the skills and training of a test pilot to just get through the day.
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Old 23rd Feb 2022, 11:35
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Originally Posted by Derfred View Post
...
In fact, the only way to save that aircraft at that point in time would be a rapid aileron roll to inverted flight, and if the subsequent negative G inverted pushover manages to avoid ground contact, the airspeed would wash off to the point that manual aft trim would be possible, and a subsequent roll to normal flight, which would have to be accomplished prior to the rapidly impending inverted stall.

Denzel Washington could have told us that, but it usually takes a fair amount of alcohol and cocaine in your system to come up with such an outside-the-square solution…
That "solution", rolling inverted, was based on the real world actions of the crew of Alaska 261 when they had a failed stab trim jackscrew. There's even a little tip of the hat by the script writers to AS261's Captain Thomson's somewhat incredulous "Are we flying?" comment after they rolled inverted when Washington's character, Whip, asks "Are we gliding?"
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Old 23rd Feb 2022, 23:35
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The stats aren’t readily available but, I’d guess that runaway trim events in 737s were relatively rare prior to the introduction of the Max. After reading various reports of incidents involving ‘unusual’ stab trim operations on the Max following it’s introduction, it is perhaps fortunate that a number of crews were able to deal with these incidents…..unfortunately two crews didn’t.

The greater issue though is that crews were challenged to respond to what appears to be a greater number of unexpected stab trim events involving a system that, at best was introduced with minimal training and information.
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Old 23rd Feb 2022, 23:42
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Aren’t we missing the point here? Neither of these accidents had a runaway trim wheel. It was feeding in nose down trim then stopping, then starting. It is not inconceivable that 10 seconds could go by whilst you are thinking ‘what the hell?’. The issue here is that the Company was guided by what was best for the bottom line as opposed to what was safest.
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Old 24th Feb 2022, 10:01
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It has been a while since I last flew the 737, but during more than a decade as a captain on type I found the 737 Technical Website an interesting source of information. The bit about runaway stabilizer reminded me of some of the details 737 Runaway Stabilizer Procedure. I watched the Netflix documentary last night and then refreshed my memory on a couple of things. A number of well qualified contributors have emphasised that if the crews had only reacted quicker with the stab trim cutoff switches everything would have been fine and indeed that this was a memory item. The technical website documents that this was originally the case at least twenty plus years ago. But in the meantime Boeing has changed the QRH a number of times and more recently the first item on the drill was to hold the control column firmly. My memory of training was that pressure against the runaway should stop the trim running. If this did not work then you moved on to the cutoff switches. The idea of reaching for them like some Wild West gunslinger is certainly not what I remember. The conclusion from the investigation that you needed to react within ten seconds on the Max to prevent a catastrophe did not ever feature during training on the classic or NG. For economic reasons Boeing did not share any information about the MCAS out of concern that this would trigger a need for additional simulator training. This together with Boeing's change of company culture from one run by engineers to one focussed on Wall Street was I think persuasively argued by the programme and fits with comments made on this site by a number of well informed insiders.

Last edited by lederhosen; 24th Feb 2022 at 14:59.
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Old 24th Feb 2022, 11:15
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Correct lederhosen. On the earlier 737 variants moving the control column against the trim runaway would / should activate column mounted cut out. The stab and associated tech and check lists is not particularly understood nor with the lack of comprehensive tech information or poorly written within FCOM adding to the confusion. The Netflix documentary is well made and is broadly accurate. The shocking aspect is the transformation from an organisation proud of its engineering expertise to a classic corporate grab fest backed up by a compromised regulator. Truly shocking MCAS was not prescribed in the FCOM and equally shocking only one source of alpha info against all basic engineering principles. I have personally heard Boeing employees attempt to blame the poor pilots in both these accidents. This is truly disgraceful. Similarly pilots should show humility and any who state here that they would have resolved these scenarios by immediately grabbing the cut out switches are talking through their @rse. I have 10,000 hours on 737s and would never be so presumptious.
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Old 24th Feb 2022, 19:14
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Genuine question, given that the Max 8 (and -800NG) is some 11m’s longer than the original -100, is it possible that the amount of runaway trim that can be allowed before the control force required to sustain flight is too great, thus meaning the time you have to recognise a runaway trim before it becomes unrecoverable is greatly reduced and outside of what the original designers intended?
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Old 24th Feb 2022, 22:00
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Good question morno and you may have a point. I have seen trim authority almost lost on the -800 simulator with a runaway stab scenario. With the caveat that the sim might not always accurately reflect the aircraft particularly at the outer edges of the envelope. One thing is certain: you need to curb the speed because if trim has runaway at a low speed and not cut out until plus 250 knots then recovery will become almost impossible due to the high air loads on the stab.
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Old 25th Feb 2022, 00:04
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Originally Posted by olster View Post
... On the earlier 737 variants moving the control column against the trim runaway would / should activate column mounted cut out.
That feature - control column movement opposing stabilizer trim stopping electric trimming - was carried through to the NG and the MAX. However, when MCAS kicks in the control column cut out is disabled as allowing manual opposite control column movement to stop the automation would prevent MCAS doing what it was designed to do.
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Old 25th Feb 2022, 05:43
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Wow! and we know Boeing deliberately decided not share to any information about the MCAS. It is hard to imagine anyone with knowledge of recent procedures thinking that was a good idea.
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Old 25th Feb 2022, 16:57
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Originally Posted by olster View Post
Correct lederhosen. On the earlier 737 variants moving the control column against the trim runaway would / should activate column mounted cut out. The stab and associated tech and check lists is not particularly understood nor with the lack of comprehensive tech information or poorly written within FCOM adding to the confusion. The Netflix documentary is well made and is broadly accurate. The shocking aspect is the transformation from an organisation proud of its engineering expertise to a classic corporate grab fest backed up by a compromised regulator. Truly shocking MCAS was not prescribed in the FCOM and equally shocking only one source of alpha info against all basic engineering principles. I have personally heard Boeing employees attempt to blame the poor pilots in both these accidents. This is truly disgraceful. Similarly pilots should show humility and any who state here that they would have resolved these scenarios by immediately grabbing the cut out switches are talking through their @rse. I have 10,000 hours on 737s and would never be so presumptious.
Hear, hear.
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Old 25th Feb 2022, 21:24
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Thanks, Krusty.
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Old 26th Feb 2022, 00:21
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On the earlier 737 variants moving the control column against the trim runaway would / should activate column mounted cut out
What determines the point of cut out, pounds of force the pilot is applying on the yoke?
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Old 26th Feb 2022, 01:29
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Originally Posted by megan View Post
What determines the point of cut out, pounds of force the pilot is applying on the yoke?
Peter Lemme has a good write up of it on his Satcom Guru website https://www.satcom.guru/2018/11/stabilizer-trim.html. He writes,

Column switches mounted forward and aft provide a means to cutout electric trim if the column is pushed too far while trimming (presumably, in opposition to the trim)
He subsequently quotes from a 1998 change release note for the FCC that references the aft column cutout position. It's probably not unreasonable to infer that the column cutout switches are likely simple positional switches rather than force sensing transducer switches.
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Old 26th Feb 2022, 04:36
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Many thanks Mick
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Old 2nd Mar 2022, 12:24
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Are Boeing still giving away ladders with every 787? Certainly would be handy.
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Old 5th Mar 2022, 04:57
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For those who've forgotten or are not too familiar with what happened on MAX accident flights and preceding Lion Air flight there’s a good summary at https://www.ntsb.gov/investigations/...ts/asr1901.pdf

For those who think they could have handled MCAS malfunction, the report also delves into Boeing’s inadequate compliance with FAR 25.1309 hazard assessment, including:

“16 While Boeing considered the possibility of uncommanded MCAS operation as part of its functional hazard assessment, it did not evaluate all the potential alerts and indications that could accompany a failure that also resulted in uncommanded MCAS operation. Therefore, neither Boeing’s system safety assessment nor its simulator tests evaluated how the combined effect of alerts and indications might impact pilots’ recognition of which procedure(s) to prioritize in responding to an unintended MCAS operation caused by an erroneous AOA input.”

EASA was rather more scathing of Boeing’s processes, assumptions and documentation in its Return to Service report
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Old 7th Mar 2022, 19:28
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Did I hear things incorrectly or did they say in Downfall that "early on, the design of MCAS was changed to use only one AOA sensor"?
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Old 7th Mar 2022, 21:04
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Originally Posted by Bmi-fan View Post
Did I hear things incorrectly or did they say in Downfall that "early on, the design of MCAS was changed to use only one AOA sensor"?
Missed that part, I’ll have to watch it again.

It does appear however to fit that “New” Boeing philosophy of profit before engineering excellence! Very sad. I wonder if the architects of the destruction of such a cornerstone of what Boeing used to stand for are able to sleep at night.

Silly question!
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