Originally Posted by
Water pilot
This seems like rather complex behavior for the pilots not to be informed about or trained on, especially in a plane that is not advertised as a fly by wire plane. When exactly does MCAS start to unwind the trim and in the worst case scenario how much uncommanded nose down trim does the pilot have to unwind if they happen to have blipped the trim switch at the wrong point in the unwind scenario?
I am not a pilot, but interesting questions (some of which I may have hinted at very early in this thread). The simple answer is that the amount of nose down trim should be limited to 2.5 degrees, and the trim unwind process should only begin once AOA is below 10 degrees.
The assumption must be that the pilot would not "porpoise" the aircraft with the elevator, alternately crossing the MCAS 10 degree AOA threshold. This criterion requires time-smoothing, to avoid random fluctuations of the AOA values (as per the new specification).
Blipping the electric trim (either up or down) during the unwind process, could theoretically put the aircraft in a semi-unstable situation, since MCAS would be disabled, and cannot reactivate again (as per the new specification). Again we must assume that the pilot intentionally wants to keep the nose high for specific reasons (such as high-altitude terrain proximity avoidance). In this scenario MCAS should not try to second guess the flight situation, but rather wait for the pilot to release the elevator yoke (and sort out any trim issues later).
Presumably the MCAS system will be clearly documented to the point where pilots are assured that:
- MCAS will not inhibit the necessary elevator yoke authority during escape maneuvers
- The overall flight system will not produce an out of trim condition when exiting from a maneuver
I seems obvious that Boeing and the FAA will flight test all of this in great detail. Whether an average pilot needs to experience this in a simulator, is an entirely different question (conditions outside the normal flight envelope). The time-delay feedback process is indeed new, and somewhat uncharted territory.