3 ms·

So if you run into this problem at 7,500’ above ground level you might just be okay. This is why having the ability to disable MCAS without disabling electric

by erentz 7y ago

So if you run into this problem at 7,500’ above ground level you might just be okay. This is why having the ability to disable MCAS without disabling electric assisted trim is so important and such a big factor in this accident. Additionally its raised another possible accident scenario: The runaway trim cutouts were put in place after electric trim in case the switch (or some other aspect of the electric trim) got stuck in an on position that would cause the trim to go to full deflection one direction or the other, hence runaway trim. And hence if you notice this happening you cutout the power to the electric trim completely. But now we know you can’t manually trim the aircraft above certain speeds with some trim levels. Should there be an expectation you can? What if runaway trim happens and ran to full deflection before a pilot cut it out. That would be equivalent to the same conditions experienced in this accident - the pilots now needing to manually trim but being unable to. So on top of needing separate cutouts for the MCAS and electric trim, should the manual trim not be investigated for installing some higher ratio gearing/pulleys to enable over coming the forces experienced here?

Gibbon1 7y ago
There is the manual trim as a backup, but it's mechanical advantage is inadequate when the trim is too far out.
- erentz 7y ago
  Right, which is why I'm saying that means there's been a failure scenario that existed even prior to MCAS. This is how they have demo'd the problem in some flight simulators for this. The electric trim can without MCAS erroneously drive the trim into this situation before being cut out. This is why the cutout switches were put in place decades ago. If this happens in some situations it could leaving the plane in a position where the trim couldn't be manually adjusted due to forces. We now know this situation also exists. Is it so rare, or resolvable in other ways, so it shouldn't be addressed? Or does there also need to be a fix for the manual trim by adjusting the gear/pulley ratio such that the pilot could overcome these forces?
  - Gibbon1 7y ago
    What I read and makes sense the way to adjust the manual trim if the force on the stabilizer is too high is to push the nose down to unload it and crank on the wheel. Probably when this was needed the pilots killed the electric trim long before it got too far out. So I agree the manual trim has always been kinda scketch.

by erentz 7y ago

Gibbon1 7y ago

There is the manual trim as a backup, but it's mechanical advantage is inadequate when the trim is too far out.

erentz 7y ago
Right, which is why I'm saying that means there's been a failure scenario that existed even prior to MCAS. This is how they have demo'd the problem in some flight simulators for this. The electric trim can without MCAS erroneously drive the trim into this situation before being cut out. This is why the cutout switches were put in place decades ago. If this happens in some situations it could leaving the plane in a position where the trim couldn't be manually adjusted due to forces. We now know this situation also exists. Is it so rare, or resolvable in other ways, so it shouldn't be addressed? Or does there also need to be a fix for the manual trim by adjusting the gear/pulley ratio such that the pilot could overcome these forces?
- Gibbon1 7y ago
  What I read and makes sense the way to adjust the manual trim if the force on the stabilizer is too high is to push the nose down to unload it and crank on the wheel. Probably when this was needed the pilots killed the electric trim long before it got too far out. So I agree the manual trim has always been kinda scketch.