I had 10 years on type at an operator with a reputable training department and this is the first I've heard of this technique.

In the real world . . .
 

. . . has anyone actually used the "roller coaster" or "yo-yo" procedure on a revenue flight?

Ostrower has a copy of the 1982 FCTM with a description of "roller coaster" technique:

https://theaircurrent.com/wp-content...-1240x1903.jpg

(main article)

I find it moderately interesting that the case chosen for evaluation is runaway nose up trim, which is an urgent stall hazard. Presumably nobody in 1982 could visualise the hazards of runaway nose down trim, perhaps due to the limited range of trim travel allowed by the autopilot in the flaps down condition. As the article notes, assumptions made five decades ago, are still propagating through today's 737 flight controls.

Thanks. How much air would want below you to have reasonable confidence in recovering in time?

How long did it take to reach that point? Doesn't sound like a quick procedure.

Not active any more but I never forgot the Convair accident due to a reversed trim:
https://www.flightglobal.com/news/ar...cables-326251/
The last weeks It crossed my mind I might have tried to trim even more nose down, in a desperate last attempt to see if the nose would come up...Which in this case would only have sped up the outcome of course...
Remember, those guys were loosing it big time, they were desperate...
Many accidents I have played back in my mind ( a kind of survival procedure for me to deal with terrible accidents), with me making the right decisions and saving the day.
But there are a few cases where I cannot find a realistic better outcome. Like JAL123. I think this MCAS affair is close to that, although technically it was survivable. But You would have to get immediately into the right direction of thinking.
How many times in YOUR career the SIM had to be stopped because Your crew was going down the drain, following a completely wrong lead? I was stopped at least once if I remember correctly....

fdr said
The design defect of immovable manual trim wheel in the pitch control system under some conditions was obviously acceptable to the FAA 50 years ago to allow certification of the B737 aircraft type.

Grandfather rights on existing certification of the B737 aircraft type has somehow allowed this defect in the flight control system to continue to exist in the modern era.

The high authority automatic MCAS system combined with the low authority manual electric trim system for the pilot to counteract the MCAS, has now shown up this "hidden" design defect in a most dreadful way.

The design defect of the immovable trim at high aerodynamic loads has been festering for 50 years awaiting a system that would reveal it to be a fatal design flaw.

Not too long. It was a while ago but I'd think 4 or 6 repeats from full stab deflection before manual trim became usable without it.
It certainly was neither violent nor extreme manoeuvering, you're only pulling to as much of a normal climb attitude as you can reasonably acheive and then relaxing back to level flight. Pax would find it a bit of an undulationperhaps like flying through wave but to call it "yo-yo' is a big exaggeration. Even roller-coaster greatly overstates it although it illustrates the shape of the thing, if you like.

Next time you're in the sim ask to try it. It's quite a gentle flightpath as you're pulling big forces on the yoke at first.
I'm surprised it disappered from the FCOM though. Mr Boing's gonna regret that decision...

Min height to do this at? 500 feet if you had to - not that you'd choose to do of course. There should be no diving or descent involved, just undulations up from and back to whatever altitude you started from. If you had height to spare ypu might use a bit of descent but it wouldn't be to my taste, I'd not want the nose below the horizon with extreme down-trim simply because of the recovery, and also to avoid airspeed buildup which would surely be obvious to most.

Has anyone read the preliminary report here? They used the electric trim 30 seconds before the crash. MCAS responded again. Airspeed was about 350 KIAS.

So, it would seem to me that if the electric trim could move the wheel, and that it can be stopped and overridden by hand power, that manual trim should have worked. 350KIAS should NOT be too fast for manual trim. Since they followed and summarily rejected the QRH and improvised, then who is at fault, or at least share fault? There was no reason to turn the electric trim switches back on, but since they did, they should have used it! If they had, they could have saved the airplane. I'll give the Lion Air guys a bit of a pass, but not much. They have a horrible reputation in the training department.

But what do I know. Six airlines in four countries on the B737 and I teach on it. Read the reports. Read them with a skeptical eye. They are surprisingly incomplete.

The report clearly states, after they turned off the stab trim, "At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough."
Then there were momentary electric trim inputs; I think they realised that they didn't have enough pitch control and decided to try the electric trim again. What would you have done? Just sat there with the switches off because that was the end of the QRH drill and slowly speared in?

I think it was a great idea switching them back on. A great pity though that they didn't follow through by trimming against the continued MCAS trim.

I would have recognized a runaway trim. Held the electric trim back until I didn't need so much control force. At the same time I'd call for the "Runaway Stab Trim" QRC/QRH. Used to be a memory item.

Both accidents used the trim to stop the motion, but NOT to reverse the trim. Anyone that hand flies the airplane much knows that you have to trim the hell out of Boeings, and trim some more. I suspect some serious training deficiencies, along with lack of experience.

I'm not buying that they could trim manually. They were doing less than 350KIAS. I suspect they didn't pull the handle out to crank it.

Therein lies a major part of the problem. Some operators actively discourage hand flying, others virtually prohibit it.

Crews with little general aviation experience just aren't getting enough practice to survive these types of events, and it's not their fault.

Trim force required isn't just dependent on IAS.

I'll subscribe to your shared responsibility argument. The legal people will split that down into percentages from the following:

1. Aerodynamic development that led to poor static stability at high AOAs.
2. Inadequately deigned software add-on (MCAS) to hide comply with static instability issue.
3. Single point of failure (AOA gauge) in safety critical flight control system.
4. Inadequate training and documentation.
5. Poor Boeing assessment of systematic failures that led to Lion Air crash - initial AD.
6. Failure by Lion Air #1 to articulate and capture problem after first, non-fatal event.
7. Regulatory oversight, lack of?
8. Two slightly dull/average/unlucky crews faced with multiple inputs.

I'll wager that the crew 'percentage' will not be the biggest number.

Time to repost this (or similar) article link every time someone also asks about:
- how do manual trim wheels, cables and the jackscrew work
- why the horizontal stabiliser is loaded via opposing elevator aerodynamic forces
- alternative techniques for unloading the HS jackscrew (roller coaster)
- why didn't the pilots do X or Y?
- can the plane fly inverted?
- why was this certified?
See: https://theaircurrent.com/aviation-s...nvestigations/

Edit: +1 for Cows getting bigger