Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.

How do you recover without unloading (diving) the aircraft?

The problem was not just the airspeed but also the extreme out-of-trim state combining to put an excessive load on the jackscrew. Once the aircraft is at or near neutral trim, manually trimming is a pain but doable. However, you absolutely need to keep ahead of it.

Even if it was possible to manually trim in their state, the crew may not have been aware of just how much force it would take. The ops manual does not provide much guidance on this. Since the Captain presumably had all his hands full with the yoke, the FO probably tried the crank handle but either could not turn it or simply did not apply enough force.

Can anyone confirm that electric trim (if enabled) could provide enough force to be able to drive the stab back from full AND at Vmo and any elevator deflection ?

Kind of sounds like it might be a certification requirement, or at least something that Boeing would have flight-tested at some stage in the last 50 years, though probably best not tried at home.

(no criticism intended or implied of the crew's decision to disable stab trim per the checklist)

This situation has been discussed elsewhere (|including by myself), and the conclusion seems to be that there are very few options left. A gradual reduction in engine thrust, to slowly reduce airspeed below 250kts is a theoretical possibility. However we do not know what effect the reduction in thrust would have on nose down pitch, due to the underslung engines. In any case, this is morbid curiousity, and should hopefully never again be encountered, particularly under these exact circumstances.

Edit: DaveReidUK There seems to be little clear data on the trim forces of a loaded horizontal stabiliser in that flight regime. More research may be needed, if the accident investigation justifies it.

Trimming electric plus manual at the same time, wasn't that the reason of the Alaska Airlines crash?
https://en.wikipedia.org/wiki/Alaska...nes_Flight_261

See how much debating is going on in both threads, see how much we have learned more about the system in the last weeks.
Those poor fellas had to find a solution in just minutes with a situation that was running out of hand big time, causing confusion and CCR breakdown. I wouldn't point a finger yet at the guys up front. Most likely I'll never will.
Let's face it, I admit honestly I wouldn't like to have been in that scenario.
Although I've have never flow 737's but nearly all of the 747 versions, I wonder if I would have made the day with the right decisions.

What trim changes occur if you pop the speedbrakes..? Nose-up..?
Then select `flaps` to lowest setting,then retrim..?As Ibelieve the MCAS only operates when the flaps are selected `up`..?

gents, anyone able to asnwer these: https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa.html#post10441180
help appreciated.

The only facts that are known (from DaveReidUK) is that one turn of the wheel equals about 0.07 trim units. That is not a misprint, 15 rotations per unit of trim.

Conversely MCAS trims down at 0.27 units per second, or 3.5 rotations of the wheel per second! That is a lot of manual winding, for every 9 second activation.

The rest will have to be officially answered by Boeing engineers.

The stab in an extreme nose down position with the elevator in a nose up position at 350KIAS would put a significant force on the stab toward the nose down position. Perhaps if the stab and elevator were closer to a trimmed condition trimming at 350 might not be a problem. High speed high deflection - different story.

What is described by the OP was taught to me (But not demonstrated ) when flying a PC6 jumpship, to defeat the classic killer of landing empty with full aft trim and forgetting to set it to half fwd for a full load take-off. Albeit a smaller plane, the PC6 has a full moving stabiliser and is subject to the same problem. This has claimed a number of lives on the dropzones.
Never heard about it on the B737 though.

[QUOTE=HalinTexas;10441177
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.
.[/QUOTE]

In my limited understanding of the B-737 MAX MCAS/trim workings, I believe that once the trim Cut Out switches are opened, the only way to trim the stabilizer is via the manual trim wheels. My friends with Boeing experience say that this is a slow and physically taxing operation. To re-trim the horizontal stabilizer quickly would require closing of the trim Cut Out switches, but, of course, that would allow the MCAS to re-initiate the nose down trim action. The pilots would have had a very small window of opportunity (maybe 5 seconds) in which to close the Cut Out Switches, trim ANU, and open the Cut Out switches before MCAS could resume commanding AND.

Just as a matter of interest, I quote from the Boeing 707 Stratoliner Flight Manual, Revision 11-8-60, entitled "Stabilizer Trim Emergency Operation":

"If the stabilizer electric trim becomes inoperative, the manual trim can be used. Due to the flight loads imposed in an out of trim condition, it may be necessary to release the control column to a low force position and retrim while in an "unloaded" condition. If the airplane is much out of trim , this action will have to be repeated until correct trim is obtained."

The manual also stated that the procedure to "Raise Nose" if the stabilizer was jammed nose down was to deactivate the inboard spoilers and raise the outboard spoilers by operating the speed brake lever.

I don't remember where or how I obtained this manual, but I've had it for 30 years or so.

Cheers,
Grog

I did ask the question about airbrakes/speedbrakes in #49,but no-one has bothered to answer.
It should be incumbent on pilots to know the effects of secondary controls...usually Lesson #2 in Basic training..
Likewise with power changes,,and flap selection in this case would have stopped the MCAS.....`Aviate` is the first consideration !!!

Will Boeing fix the stuck manual trim problem?

Will the FAA de-certify the B737 series aircraft until the stuck manual trim problem is resolved?

Or perhaps, the subject will be quietly buried, to wait for a future opportunity for the problem (inability to manually trim the stabiliser throughout the whole flight envelope) to re-emerge?

Speedbrakes being so close to the CP will not induce a big pitch moment in either direction.

They will kill quite a lot of lift, meaning they will cause the aircraft ROC diminish or even turn the other way all things equal, not what the pilots were looking for.