Originally Posted by
Loose rivets
Weeks ago a poster put forward a series of comments which ended with (roughly) "So MCAS is not an anti-stall device . . . but it is, sort of."
Well, that about sums up the fuzziness of the public perception.
I think a big part of the problem is that words employed in common usage may have more specific meanings in the world of aircraft certification. In a sense, any system that helps keep an aircraft away from the stall environment (for example, autothrottle alpha floor protection, stick shaker, visual and/or audio alerts, etc) could be generically called an "anti-stall" device. However, strictly from a certification standpoint I'm not sure there is even a definition for an "anti-stall" system, much less a requirement. On the other hand, I know there are requirements that commercial aircraft have stall warning systems and demonstrate certain handling characteristics approaching and recovering from a stall.
MCAS exists because of requirement for a linear control feel response through the high AOA environment. To the extent that someone wants to call this an "anti-stall" system and there is no conflicting definition in the FAR's, then I guess there is no harm.
However, in some cases words really do mean something, hence my interest when someone claims the 737 is "unstable." There are very specific definitions of what stability means, and there is no evidence that the 737 demonstrates anything but positive static stability through its flight envelope. I would accept the premise that the this positive stability
may trend toward neutral stability approaching high AOA values, but it never goes negative.