3 ms·

MCAS trimmed it so much that the pilots were unable to bring it back manually. Not only that, MCAS controlled an electric motor which turned the trim wheel and

MCAS trimmed it so much that the pilots were unable to bring it back manually. Not only that, MCAS controlled an electric motor which turned the trim wheel and which could apply more torque than a human turning it manually. The only way to disable MCAS was to cut power to that motor. MCAS pointed the aircraft at the ground, and it was impossible to trim the aircraft to achieve level flight again. Mind, MCAS was supposed to be a crutch to fly at the edges of the flight envelope, something that a regular pilot would never encounter because under normal conditions pilots wouldn't find themselves in a regime where MCAS would be activated. That was the idea, instead we had two hull losses within 6 months!

Obi_Juan_Kenobi 8y ago
The electric trim adjustment is obviously going to be more powerful, that's just the reality of large planes. That's not the issue. The issue from the Ethiopian crash was that, in the extreme trim angle, there was simply too much force on the screw to turn manually. This condition is trained for, and the solution is to let the plan angle down to relieve the aerodynamic pressure on the control surface. That gives you an opportunity to manually control the trim wheels. The pilots did not have the benefit of altitude to perform this maneuver, so (likely) instead re-enabled the electric trim in a bid to use it to reduce the nose-down trim before the MCAS would re-engage. This proved fatal.
- matt-attack 8y ago
  Are you suggesting with the auto-trim disabled, the two pilots working together, with those handles extended on the trim wheel, were not strong enough to crank the trim wheel?
  - cmurf 8y ago
    Yes. Known issue. Scroll down slightly for the empennage diagram, right hand side, item 3. https://www.seattletimes.com/business/boeing-aerospace/boeings-emergency-procedure-for-737-max-may-have-failed-on-ethiopian-flight/ https://www.seattletimes.com/business/boeing-aerospace/boein...

Obi_Juan_Kenobi 8y ago

The electric trim adjustment is obviously going to be more powerful, that's just the reality of large planes. That's not the issue. The issue from the Ethiopian crash was that, in the extreme trim angle, there was simply too much force on the screw to turn manually. This condition is trained for, and the solution is to let the plan angle down to relieve the aerodynamic pressure on the control surface. That gives you an opportunity to manually control the trim wheels. The pilots did not have the benefit of altitude to perform this maneuver, so (likely) instead re-enabled the electric trim in a bid to use it to reduce the nose-down trim before the MCAS would re-engage. This proved fatal.

matt-attack 8y ago
Are you suggesting with the auto-trim disabled, the two pilots working together, with those handles extended on the trim wheel, were not strong enough to crank the trim wheel?
- cmurf 8y ago
  Yes. Known issue. Scroll down slightly for the empennage diagram, right hand side, item 3. https://www.seattletimes.com/business/boeing-aerospace/boeings-emergency-procedure-for-737-max-may-have-failed-on-ethiopian-flight/ https://www.seattletimes.com/business/boeing-aerospace/boein...