“What the Lion Air Pilots May Have Needed to Do to Avoid a Crash” (nytimes) contains a lot of good cockpit photos and illustrations explaining the combination of manual and automatic flight controls that likely played a role in the recent Boeing 787 MAX 8 crash (see https://philip.greenspun.com/blog/2018/11/11/boeing-737-crash-is-first-mass-killing-by-software/ ).
If it sensed a stall, the system would have automatically pushed up the forward edge of the stabilizers, the larger of the horizontal surfaces on the plane’s tail section, in order to put downward pressure on the nose.
To counter the nose-down movement, the pilot’s natural reaction would probably have been to use his yoke, which moves the other, smaller surfaces on the plane’s tail, the elevators. But trying that maneuver might well have wasted precious time without solving the problem because the downward force on the nose exerted by the stabilizer is greater than the opposite force the pilot would be trying to exert through the elevator, said Pat Anderson, a professor of aerospace engineering at Embry Riddle.
“After a period of time, the elevator is going to lose, and the stabilizer is going to win,” he said.
(The same guy gave an interesting lecture this summer; see “Transitioning to electric flight (lectures at Oshkosh)”.)
The pictures show a mix of 1950s (the big trim wheel), 1980s (the switch-controlled trim and trim interrupt), and 1990s (the MCAS layered on top that puts in heavy trim silently).
My comment on the NYT piece:
I sometimes fly the Pilatus PC-12, a simple 11-seat turboprop. Its stall-protection system was designed in the early 1990s. There are two angle-of-attack (AOA) sensors, one on each wing. There are two computers, each one of which is connected to a single AOA sensor. Only if both AOA sensors show a stalling angle of attack (“nose too high”) AND both computers agree THEN there will be a “stick push”. Thus there could never be a nose-down push due to a single bad AOA sensor. In the unlikely event that both sensors and/or computers went haywire at the same time, there is a “pusher interrupt” switch right on the yoke (“stick”). So the pilot need not hunt for an out-of-sight and never-previously-used switch.
It sounds as though Boeing engineered something that relies on just one sensor.
Plainly the Pilatus-style system would not have interfered with these 189 souls making their way safely to the destination. I wonder if a simple voice annunicator on top of the Boeing system would have also saved the passengers and crew. If it had said “trimming down, trimming down” into the headsets, the pilots would have known to direct their attention to the trim and trim interrupt switches.