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Will this test whether pilots have the upper-body strength necessary to manually turn the cockpit trim wheels considering the size and aerodynamic forces for th

Will this test whether pilots have the upper-body strength necessary to manually turn the cockpit trim wheels considering the size and aerodynamic forces for this large an aircraft? Unless there has been some change other than to MCAS, the manual trim wheels are still the only option to correct runaway horizontal stabilizers.

michaelcampbell 7y ago
Surely it is possible to provide them with a mechanism that gives enough mechanical advantage. I have a vision of... dissimilar sized gears, or something...
- fgonzag 7y ago
  I'm imagining the pressure inside sealed tubes filled with liquid could be exploited to provide a force multiplier
- lmilcin 7y ago
  You mean an airplane of a different design that would need to be separately certified?
  - fgonzag 7y ago
    It wouldn't. The trim wheel would work exactly the same from the pilot's perspective. It would only work different internally.
    - CheesecakeFred 7y ago
      The gear ratio would change. Also I can't imagine certification is only required for changes from a pilot's perspective, but from a functional perspective.
- kayfox 7y ago
  Like electric motors controlled by the pilots?
tzs 7y ago
My understanding is that you only get the large forces when you have a large amount of trim and are going fast. On 737's without MCAS, the only way runaway trim would get anywhere near that would be if the pilots ignored it for a long time. What MCAS added was that it could keep reactivating. You got what looked like runaway trim, stopped it, and a few seconds later MCAS would kick in again. Each cycle of this could end up accumulating net trim until you got into the high force region and could no longer manually turn the trim wheels.
mannykannot 7y ago
The manual trim wheels are not necessarily the only option in that case. If the runaway is due to faulty MCAS commands, the electric trim (operated by the yoke switches) is probably still functional, so I believe it is possible that the procedures for handling MCAS failure have been modified, now that Boeing is no longer pretending that MCAS makes no difference. In addition, I believe MCAS itself has been modified. I have not seen a clear description of the changes, but they might include additional redundancy, rejection of improbable data, warnings that there are these problems, warnings whenever MCAS activates, restrictions on how much it can change the trim, and a cutout switch for MCAS that keeps the electric trim functioning. In the worst case, manual retrimming with the wheels is still the last resort. I have seen it suggested, by sources generally considered reliable, that (prior to the Max) the need for the manual trim has been so rare that its use is not part of simulator training for any 737. I do not know if that will change, but if so, it would seem to raise the question of whether pilots of earlier variants also need additional training in its use (I would guess that it is most difficult on the largest and heaviest variants.)

michaelcampbell 7y ago

Surely it is possible to provide them with a mechanism that gives enough mechanical advantage. I have a vision of... dissimilar sized gears, or something...

fgonzag 7y ago
I'm imagining the pressure inside sealed tubes filled with liquid could be exploited to provide a force multiplier
lmilcin 7y ago
You mean an airplane of a different design that would need to be separately certified?
- fgonzag 7y ago
  It wouldn't. The trim wheel would work exactly the same from the pilot's perspective. It would only work different internally.
  - CheesecakeFred 7y ago
    The gear ratio would change. Also I can't imagine certification is only required for changes from a pilot's perspective, but from a functional perspective.
kayfox 7y ago
Like electric motors controlled by the pilots?

tzs 7y ago

My understanding is that you only get the large forces when you have a large amount of trim and are going fast. On 737's without MCAS, the only way runaway trim would get anywhere near that would be if the pilots ignored it for a long time. What MCAS added was that it could keep reactivating. You got what looked like runaway trim, stopped it, and a few seconds later MCAS would kick in again. Each cycle of this could end up accumulating net trim until you got into the high force region and could no longer manually turn the trim wheels.

mannykannot 7y ago

The manual trim wheels are not necessarily the only option in that case. If the runaway is due to faulty MCAS commands, the electric trim (operated by the yoke switches) is probably still functional, so I believe it is possible that the procedures for handling MCAS failure have been modified, now that Boeing is no longer pretending that MCAS makes no difference. In addition, I believe MCAS itself has been modified. I have not seen a clear description of the changes, but they might include additional redundancy, rejection of improbable data, warnings that there are these problems, warnings whenever MCAS activates, restrictions on how much it can change the trim, and a cutout switch for MCAS that keeps the electric trim functioning. In the worst case, manual retrimming with the wheels is still the last resort. I have seen it suggested, by sources generally considered reliable, that (prior to the Max) the need for the manual trim has been so rare that its use is not part of simulator training for any 737. I do not know if that will change, but if so, it would seem to raise the question of whether pilots of earlier variants also need additional training in its use (I would guess that it is most difficult on the largest and heaviest variants.)