Originally Posted by
GordonR_Cape
Thanks for the very interesting input! I'm not a pilot but a programmer. From a Control System perspective it seems very difficult to define a single 'event'. Does it last for 30 seconds or 5 minutes? If an aircraft approaches stall twice, does the behaviour of the first MCAS event inhibit the second one?
The more constraints are put into a system, the more possibilities there are for ending up in a logical conundrum. What may be obvious to a human is not so clear to a computer. IMO fixing MCAS may mitigate the potential for disaster, while still leaving unanticipated outcomes in the system.
Just my 2c.
Another part of MCAS functionality that has not gotten much coverage is how it recovers and moves the stabilizer back in the airplane nose up direction once the high AOA event that triggered MCAS in the first place no longer exists. MCAS keeps track of how much stabilizer motion in the airplane nose down direction it has commanded (either all at once for a rapid AOA increase of as a number of shorter trim inputs for a slower AOA increase - see my entries above in this thread). Once AOA has dropped back below the MCAS activation point it will begin running the stabilizer in the airplane nose up direction to take out what it has put in. This will proceed until the stabilizer is back where it started from before MCAS activation provided the flight crew does not make a trim input. Any trim input causes MCAS to stop its command and reset, ready to go again when it next sees the activation criteria of Flaps Up, Autopilot Disconnected, and AOA above MCAS activation threshold.