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Ethiopian MAX Crash Simulator Scenario Stuns Pilots

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Ethiopian MAX Crash Simulator Scenario Stuns Pilots

Old 13th May 2019, 14:32
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Ethiopian MAX Crash Simulator Scenario Stuns Pilots

Aviation Week has published an interesting article where some us pilots have recreated the out of trim problem facing the Ethiopian pilots on the later stage of the ET 302 flight.
They found that it was impossible to trim with the trim wheel starting the sim session at 10,000 feet and 250 knots (IA?) with the stabilizer set to 2 degrees/units. They then resorted to the roller coaster method and was successfull in trimming the stabilizer, but in this process they lost 8,000 of the available 10,000 feet of height.

The article discusses the lack of information regarding this roller coaster method and how difficult it is to recover from a severe out of trim state with the manual trim wheels only.

AW article simulated ET302 flight
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Old 13th May 2019, 14:54
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That should make an interesting read. Why not use the electric trim?
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Old 13th May 2019, 14:57
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Originally Posted by Icarus2001
That should make an interesting read. Why not use the electric trim?
Doesn't the procedure call for trim cutout switches off?
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Old 13th May 2019, 15:05
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Amongst the various thread closures - I know not why !!!
The following is in Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim

Link -
https://aviationweek.com/commercial-aviation/ethiopian-max-crash-simulator-scenario-stuns-pilots?NL=AW-05&Issue=AW-05_20190513_AW-05_525&sfvc4enews=42&cl=article_1&utm_rid=CPEN1000002344541& utm_campaign=19626&utm_medium=email&elq2=32716dd5cd31477aa8b 3175d28a7b54a

Highlights for the non registered (free).

A simulator session flown by a U.S.-based Boeing 737 MAX crew that mimicked a key portion of the Flight 302 accident sequence suggests that the crew faced a near-impossible task of getting their 737 MAX back under control, and underscores the importance of pilots understanding severe runaway trim recovery procedures.’

‘What the U.S. crew found -. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn.
They resorted to a little-known procedure to regain control.’
(YoYo Roller Coaster)

The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery.

The article continues discussing aspects of the recent accidents, worthy of inclusion in many of the previous (closed) threads; failing that - register for info.

Concluding

The simulator session underscored the importance of reacting quickly to uncommanded stabilizer movements and avoiding a severe out-of-trim condition, one of the pilots involved said. “I donʼt think the situation would be survivable at 350 kt. and below 5,000 ft,” this pilot noted.’

“This is the sort of simulator experience airline crews need to gain an understanding of how runaway trim can make the aircraft very difficult to control, and how important it is to rehearse use of manual trim inputs,”


Icarus2001, gear-lever,
Re procedures, elect trim, trim disabling see Evolution of 737 Runaway Trim Procedure.
And particularly the closed thread 737 Trim
Trying to pull the thread loose ends together.

Last edited by safetypee; 13th May 2019 at 15:19.
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Old 13th May 2019, 15:18
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Originally Posted by safetypee
Amongst the various thread closures - I know not why !!!
The following is in Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim

Link -
https://aviationweek.com/commercial-...b3175d28a7b54a

Highlights for the non registered (free).

A simulator session flown by a U.S.-based Boeing 737 MAX crew that mimicked a key portion of the Flight 302 accident sequence suggests that the crew faced a near-impossible task of getting their 737 MAX back under control, and underscores the importance of pilots understanding severe runaway trim recovery procedures.’

‘What the U.S. crew found -. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn.
They resorted to a little-known procedure to regain control.’
(YoYo Roller Coaster)

The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery.

The article continues discussing aspects of the recent accidents, worthy of inclusion in many of the previous (closed) threads; failing that - register for info.

Concluding

The simulator session underscored the importance of reacting quickly to uncommanded stabilizer movements and avoiding a severe out-of-trim condition, one of the pilots involved said. “I donʼt think the situation would be survivable at 350 kt. and below 5,000 ft,” this pilot noted.’

“This is the sort of simulator experience airline crews need to gain an understanding of how runaway trim can make the aircraft very difficult to control, and how important it is to rehearse use of manual trim inputs,”


Re procedures, see Evolution of 737 Runaway Trim Procedure.
Trying to pull the thread loose ends together.
All works fine on the iPad.
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Old 13th May 2019, 15:29
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Reply to pattern is full, in closed thread #6 737 Trim
Re ‘With which we can compare the available trimming force available (motor power or pilot muscle).’

Pilot muscle - relates to trim wheel, but for failure cases, the combined wheel - muscle on the tail plane would also be offset by the opposing ‘muscle’ of nose up elevator : you probably meant that, the diagrams at https://www.satcom.guru/2019/04/stab...and-range.html explain this better than I might have.

The changes in tail-surface area are interesting; presumably to accommodate longer fuselage, changed aero dynamics, installed thrust. All of which could alter the effectiveness of trim - hence need to update the trim runaway drill.
The magnitude of aero / engine changes in the Max required MCAS; even more nose up pitching moment.
This suggests the need for a significant review of the emergency drill, which the FAA proposes.

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Old 13th May 2019, 15:47
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Reply to Dave Reid UK at #9 737 Trim

Re ‘If it's a "fact" that electric trim can't move the stab back towards a trimmed state, either, then can we have some non-anecdotal evidence of that, please ?

This is the crux of this thread #1 (737 trim); ‘… how do we know with any certainty?’
You correctly identify ‘ability’ - the systems capability - force (in each direction) opposed to the limiting, range - angular distance;

It is probable that ‘facts’ don’t exist. The extreme emergency-failure situation being considered may not justify flight testing (hazardous).
The combined technical / aerodynamic knowledge, systems ‘Iron Bird’ tests (fact), and actual flight tests approaching the extreme conditions (fact), would contribute to a ‘model’ of the aircraft which would predict the limit case (unknown accuracy - assumption of acceptability).
If the aircraft / trim system performance was predicted as being beyond the requirements of safety certification then alternative protections and/or procedures could be proposed. These would require validation.
Thus in this case, by limiting the exposure of elect trim failure - stick switches, cutout system, and - most critically - checking the assumptions about human involvement of failure recognition and use of the procedure.

How much credit can be taken for pilot intervention intervention, how is this tested / validated.???

The human aspect is alway open to question; particularly with evolving series of aircraft. Based on the other trim runaway-drill discussions, it is possible that the assumptions made for later versions of the 737 now justify challenging; particularly when viewed against the backdrop of a changing industry, operations, training, and the effect on all of these these of modern technologies.
It’s extremely unlikely that the human has changed, but the surrounding circumstances will have. Circumstance includes training, not as an individual because of the difficulty in ensuring consistent response irrespective of individual pilots’ training / experience - HF.
Where the line of safety is approached or crossed (manufacturing, certification, operational, judgement - no certainty), then it will be necessary to reconsider the design - not the human.

The ‘ certainty / uncertainty’ being discussed is not about a factual line - it’s about who judges, how is this best done, and are decisions - assumptions revisited (by grandchildren).
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Old 13th May 2019, 17:41
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Originally Posted by safetypee

‘What the U.S. crew found -. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn.
They resorted to a little-known procedure to regain control.’
(YoYo Roller Coaster)

The excessive descent rates during the first two steps meant the crew got as low as 2,000 ft. during the recovery.

[...]
The simulator session underscored the importance of reacting quickly to uncommanded stabilizer movements and avoiding a severe out-of-trim condition, one of the pilots involved said. “I donʼt think the situation would be survivable at 350 kt. and below 5,000 ft,” this pilot noted.’

“This is the sort of simulator experience airline crews need to gain an understanding of how runaway trim can make the aircraft very difficult to control, and how important it is to rehearse use of manual trim inputs,”

kind of curdles the innards a little bit to read that, no?
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Old 13th May 2019, 19:19
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Can someone explain why slowing down to reduce the control force not an option ?
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Old 13th May 2019, 19:34
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Originally Posted by swh
Can someone explain why slowing down to reduce the control force not an option ?
Two reasons:
1. A pilot cannot be expected to operate the throttles if a rogue system mis-trims the aircraft; too much attention has been diverted.
2. It is not in the runaway trim NNC. Therefore a pilot should not be expected to do it.
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Old 13th May 2019, 20:12
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2. It is not in the runaway trim NNC. Therefore a pilot should not be expected to do it.
Then the next question is: should it be?
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Old 13th May 2019, 20:16
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Discussed here and in Tech Log for more than a month.

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