6 ms·
> 1. Use inputs from both AOA sensors, if they disagree by 5.5 degrees, disable MCAS. Great, and now you have the other problem the MCAS was supposed to mitiga
by tus87 7y ago
> 1. Use inputs from both AOA sensors, if they disagree by 5.5 degrees, disable MCAS.
Great, and now you have the other problem the MCAS was supposed to mitigate (the tendency of the MAX to do backflips).
- noir_lord 7y agoShrugs, if the MCAS disables with a clear notification to the pilots I think at this point most 737-Max pilots would know the procedure to deal with that. Better than the plane flying itself into the ground.
- tus87 7y agoWhich raises a rather obvious question ...
- vkou 7y ago> Shrugs, if the MCAS disables with a clear notification to the pilots I think at this point most 737-Max pilots would know the procedure to deal with that. The plane is only certified to be 'identical to the 737' when MCAS is on, and operating correctly. If MCAS has to be disabled in response to a common mechanical problem, then the plane must be re-certified.
- cjrp 7y agoAlthough at least now you're trying to solve a more logical problem. Increasing angle of attack => counter with elevator, if not sufficient reduce thrust
- foldr 7y agoReducing thrust will increase angle of attack. The angle of attack is the angle of the wing relative to the airflow, not the angle of the plane relative to the horizon.
- salawat 7y agoYes conceptually, no because of signage error. If you were in a position MCAS would have to kick in, you were at positive AoA, reduced thrust would impart a negative AoA moment.
- cjrp 7y agoExactly, I'm only talking about in the MCAS-scenario.
- foldr 7y ago> you were at positive AoA, reduced thrust would impart a negative AoA moment I don't think that is correct. I think you're still thinking of the angle of the plane with respect to the horizon, not the AoA. If reducing thrust reduced AoA, then you could recover from a stall by reducing thrust. In reality, the opposite is the case. The only way to recover from a stall by manipulating engine thrust is to increase it (though this won't always be sufficient by itself).
- pas 7y agoAFAIAK the procedure is to not increase thrust, quite the opposite (disable the autothrust thingie), get the nose below the "horizon" (which is of course wind dependent), gain airspeed, and then start to increase thrust (which will automatically start to up the nose a bit), then climb back to whatever altitude you should be at.
- foldr 7y agoI don't mean to say that increasing thrust is the standard stall recovery procedure in most aircraft, or that all stalls could be recovered from merely by increasing thrust. But if one could only manipulate thrust, one would increase thrust to recover from a stall, not decrease it.
- pas 7y agoAh, yes, of course, theoretically if you can just increase thrust arbitrarily, that always solves the issue. (Again, of course, this might mean the whole plane becomes a rocket because the wings already fell off, so you might need some thrust vectoring too.)