Originally Posted by
YYZjim
From (only) a private pilot. I find prose descriptions of technical systems hard to follow, and prefer diagrams, schematics and flowcharts. I still do not fully understand the pitch control on 737 NGs and MAXs. The following diagram helped me, but likely contains errors and misunderstandings. Comments would be appreciated.
1. Does the autopilot operating in "normal" flight mode (excluding its STS and Mach Trim trimming) move the elevators or the stabilizer?
2. Does flipping the CUTOUT switch terminate the autopilot's control of the elevators or just its control of the stabilizaer jackscrew?
3. I have read about a "hidden" switch somewhere on the back of the center console that did something on the NG, but has been removed on the MAX. What is it?
4. I have read that the First Officer's trim switch is actually a pair of switches. If true, do the separate switches do different things?
5. I have read that the MAX has an automatic Elevator Jam Landing Assist system which manipulates the spoilers to assist in pitch control. The EJLA looks after things when the flaps are deployed; the MCAS looks after things when they're not. Hmmm. I wonder if there is an unintended software interaction?
We need a FAQ for this topic. I am not a pilot, but these are what I have read.
1. The autopilot can move any control it likes, within limits.
2. The trim cutoff switch only controls the horizontal stabiliser, not any other flight controls.
3. There is an underfloor cutoff switch at the bottom of the control column. It is still there, but its function changed on the MAX.
4. Each pilot's electric trim consists of two thumb-switches mounted close together. For each pilot, both have to be pressed for any action to occur.
5. No answer.