[simcop2387]

Found a forum thread about it from some aviation enthusiasts [1]. Some choice excerpts they made:

‘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 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,”

[1] https://www.pprune.org/rumours-news/621478-ethiopian-max-cra...

[janoc]

This video by a 737-NG captain shows the kind of forces you get:

https://www.youtube.com/watch?v=aoNOVlxJmow

It is not MAX but the systems are identical.

That's why it is so essential to recognize and stop the runaway trim (for whatever reason) ASAP or you could get into a situation where it would be physically impossible for the crew to do so.

[debt]

Can someone shed light on what the "little-known procedure" is they're referring to?

[112012123]

Most likely aerodynamically relieving trim wheel pressure by intentionally letting the nose of the plane drift down. This allows the pilots to more easily crank the trim wheel and fix the issue.

If I remember correctly, this procedure was specifically described in older 737 manuals, but had been dropped more recently.

[theclaw]

It's a "roller coaster" procedure where the plane is pitched down to lessen aerodynamic forces on the stabiliser, allowing the trim wheels to be manually turned, then pitched up to regain altitude. The process is repeated as necessary until the trim wheels can be manually moved without it.

[AYBABTME]

Interesting, it seems similar to how large sailboats need to head into or down wind when attempting to trim sails in some conditions? (to reduce pressure on the sails to allow trimming to be doable by hand)

[Zeebrommer]

Yeah, with the important difference that in sailing you lose speed (and heel) when heading into the wind, whereas a plane will go even faster towards the ground... Scary!

[janoc]

Yes. Mentour mentions it in the video I have posted above.

You unload the stabilizer by pitching down for a few seconds so that you can trim it back somewhat.

However, that is not something you can do close to the ground (you lose altitude, obviously) and the "vomit comet" ride won't be appreciated by the passengers neither.

[esaym]

Basically in this situation, even though the nose of the plane is uncontrollably pointing down, to get it to rise again requires that you momentarily push the nose down even further to allow the trim control to unjam and start working again.

[snthd]

https://theaircurrent.com/aviation-safety/vestigal-design-is...

[mrtksn]

If I remember correctly, this is a procedure that once was on the 737 flight manual as an recommended procedure but later Boeing removed it. I recall reading about in an article here at HN.

[Jabbles]

Did they do it on their first attempt?