Originally Posted by
Bend alot
If MCAS will still have a maximum 9 second run time and a pilot should cut it in 3 seconds - what is the other 6 seconds of MCAS operation still required for?
The short answer is that the other 6 seconds was driven by the FAR 25 certification requirement. There is a specific region approaching a stall over which the control forces must have a linear slope gradient whether or not there is a realistic expectation that the pilots would ever get into this corner of the flight envelope. That was the entire reason for MCAS’s existence.
Functionally, I think this 6 seconds would be superfluous in any actual approach to stall because there is also an expected reaction time to a legitimate stall warning. I don’t actually know what the FAA standard is, but a pilot shouldn’t need 9 seconds to figure out whether the aircraft is actually stalling when the stick shaker activates. Part of the stall recovery procedure involves unloading the aircraft (release back pressure at a minimum, but likely a strong push) accompanied by trim as necessary. Both of these actions would terminate the MCAS input before its full run.
On the other hand, if the pilots are somehow so distracted that they do not register what the stick shaker and aircraft energy state are telling them, I doubt they are going to pick up on the stab movement either. In that case, a full MCAS run will likely save their bacon.