4 ms·

During otherwise normal flight conditions, the nose might unexpectedly pitch up. MCAS is designed to prevent that when AoA > somevalue to prevent stalling.

Zak 8y ago
During normal flight conditions, the nose does not pitch up beyond the pilot's ability to control with the elevator, and the pilot doesn't fly especially close to the critical angle of attack. MCAS is for an unusual combination of conditions where both elevator and trim might be needed to reduce the angle of attack. An example would be if the pilot set a fairly high nose-up trim to maintain the slow speed of final approach, then decided to go around (abort the landing), applied full thrust, and fully raised the flaps too early. A pilot would definitely know that using trim is an option if the elevator was not producing enough nose-down pitch, but a pilot who has put the aircraft into the situation where a stall is imminent during a passenger flight has already made a series of errors.
- linuxftw 8y ago
  > An example would be if the pilot set a fairly high nose-up trim to maintain the slow speed of final approach, then decided to go around (abort the landing), applied full thrust, and fully raised the flaps too early. This scenario seems it would apply to previous generation 737s as well. But for some reason, MCAS was required for the MAX 800. Everything I have read so far indicates the MAX 800 has some 'pitch up on it's own' type problem that can lead to a stall. So while I'm sure it's possible to crash the plane in a variety of ways, none of that has to do with MCAS.
  - Zak 8y ago
    All 737s have a nose-up pitch moment from the thrust of the engines because they're hanging under the wings. The engines of the MAX are more powerful, and positioned differently resulting in a stronger nose-up moment. The elevator is not enough to overcome the nose-up pitching moment of the MAX under certain conditions, but the trim is.

Zak 8y ago

During normal flight conditions, the nose does not pitch up beyond the pilot's ability to control with the elevator, and the pilot doesn't fly especially close to the critical angle of attack. MCAS is for an unusual combination of conditions where both elevator and trim might be needed to reduce the angle of attack. An example would be if the pilot set a fairly high nose-up trim to maintain the slow speed of final approach, then decided to go around (abort the landing), applied full thrust, and fully raised the flaps too early. A pilot would definitely know that using trim is an option if the elevator was not producing enough nose-down pitch, but a pilot who has put the aircraft into the situation where a stall is imminent during a passenger flight has already made a series of errors.

linuxftw 8y ago
> An example would be if the pilot set a fairly high nose-up trim to maintain the slow speed of final approach, then decided to go around (abort the landing), applied full thrust, and fully raised the flaps too early. This scenario seems it would apply to previous generation 737s as well. But for some reason, MCAS was required for the MAX 800. Everything I have read so far indicates the MAX 800 has some 'pitch up on it's own' type problem that can lead to a stall. So while I'm sure it's possible to crash the plane in a variety of ways, none of that has to do with MCAS.
- Zak 8y ago
  All 737s have a nose-up pitch moment from the thrust of the engines because they're hanging under the wings. The engines of the MAX are more powerful, and positioned differently resulting in a stronger nose-up moment. The elevator is not enough to overcome the nose-up pitching moment of the MAX under certain conditions, but the trim is.