Originally Posted by
QuagmireAirlines
They didn't need to turn it off. Not stalling. Pitch was high, yet with an empty aircraft, velocity vector was high too.
It does raise a related issue: What pitch angle and/or vertical speed should MCAS be safely disabled?
I might have implemented a disable for pitch angle < 6 degrees, and possibly add an AND condtion with vertical speed < 0 which would keep the nose from auto-trimming down when descending at a low or negative pitch angle.
What condition would you disable MCAS down-trim on? Boeing isn't buying any of that of course, yet doesn't keep us from suggesting something else.
There is confusion on this thread.
MCAS is not to stop the aircraft stalling - it is to ensure that the correct number of pounds of force are required on the control column per knot of airspeed increase/decrease. This may have the effect of preventing a pilot pulling into a stall (particularly a high speed stall) but MCAS was there to meet 14 CFR 25.173 which reads:
§25.173 Static longitudinal stability.
Under the conditions specified in §25.175, the characteristics of the elevator control forces (including friction) must be as follows:
(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC/MFC, whichever is appropriate, or lower than the minimum speed for steady unstalled flight.
(b) The airspeed must return to within 10 percent of the original trim speed for the climb, approach, and landing conditions specified in §25.175 (a), (c), and (d), and must return to within 7.5 percent of the original trim speed for the cruising condition specified in §25.175(b), when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.
(c) The average gradient of the stable slope of the stick force versus speed curve may not be less than 1 pound for each 6 knots.
(d) Within the free return speed range specified in paragraph (b) of this section, it is permissible for the airplane, without control forces, to stabilize on speeds above or below the desired trim speeds if exceptional attention on the part of the pilot is not required to return to and maintain the desired trim speed and altitude.
[Amdt. 25-7, 30 FR 13117, Oct. 15, 1965]
There is nothing in this regulation about Stall. It is expected that one of the effects of the specified pull forces will be pilots less likely to pull into a stall, but the regulation does not mention stalling.