Boeing 737 Unable to Trim!! Cockpit video (Full flight sim)

Well, the "Stabilizer wheel - grasp and hold" item of the procedure doesn't necessarily mean the crew will be able to override it. That's the last ditch option on the checklist, when everything else has failed, even turning the motors off (there could be e.g. a short circuit powering the motor). There is no clutch on the 737, AFAIK, because the forces are such that it wouldn't work. Here is a good video by an actual 737 captain explaining how the runaway stab trim procedure works and what you have to do. [LINK] And this simulator video shows both how the 737 horizontal stabilizer is controlled and what kind of forces are on the trim wheel and control column when severely out of trim: [VIDEO] Should give you an idea what were the Ethiopian pilots facing when unable to use the electric trim, plane trimmed nose heavy by MCAS and at high speed ...

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

Depends on the aircraft. Some modern jetliners are using fly-by-wire, while others have hydraulically-boosted controls. Some still rely on cable-and-pulley. Either way, as I understand, it wouldn't matter with the MCAS-related MAX aircraft crashes. The elevator trim is able to move the entire elevator (literally, the entire elevator moves in response to the jackscrew controlled by the trim system) to such an extent that, depending on CG, airspeed, and other factors, it cannot be overpowered by moving the control surface to its full deflection. So whether or not the MAX had boosted controls or fly-by-wire probably wouldn't have mattered in the case the aircraft were trimmed fully nose-down. The pilots would have been struggling to maintain control either way. That's why there's stabilizer trim cut-out switches and manual trim. I'd highly recommend Mentour Pilot's videos on the subject, links below: Runaway Stabilizer: How to stop MCAS - [LINK] Boeing 737 Unable to Trim! Cockpit video (full flight sim) - [VIDEO] Five questions about the Boeing 737 MAX Answered - [LINK]

> ... it can become impossible for a pilot to physically turn the manual trim wheels to get back into trim I feel like this isn't talked about enough. I had no idea how bad it can actually get: [VIDEO]

Mentour Pilot has a video where he does that exact simulation for a 737NG flight simulator in order to show how difficult it is to trim manually [1]. [1] [VIDEO]

> Boeing 737 Unable to Trim! Cockpit video (full flight sim) - [VIDEO] Start at 13:20 to skip straight to the relevant bit.

Very good points. And in the case of MCAS, physically unable to exert the effort to overcome the automated trim settings. (Posted above): [VIDEO]

Even more than that, you pick up speed due to the nose down configuration. This means the forces on the control surfaces are so great that you can no longer manually trim via the trim wheels. This was, apparently, a well known handling characteristic of the 737, with original versions describing a "roller coaster" maneuver where you dive briefly to relieve the forces on the control surfaces and incrementally trim. Unfortunately, because of how MCAS was set up, it was inactive while flaps were set, but kicked in immediately upon flaps up, meaning that they essentially had no altitude to work with. See: [VIDEO] for a flight sim recreation of this situation on an NG. Everything here seems to be that exceptional pilots can (and did) save the situation, but that it's not straightforward even with training.