737 MAX Flight Crew Operations Manual
Flight Controls -
System Description
MN-FLT-OH-201
9.20.13
Stall Identification
Stall identification and control is enhanced by the yaw damper, the Elevator Feel
Shift (EFS) module and the Speed Trim System. These three systems work
together to help the pilot identify and prevent further movement into a stall
condition.
During high AOA operations, the Stall Management/Yaw Damper (SMYD)
reduces yaw damper commanded rudder movement.
The EFS module increases hydraulic system A pressure to the elevator feel and
centering unit during a stall. This approximately doubles control column forces.
The EFS module is armed whenever an inhibit condition is not present. Inhibit
conditions are: on the ground, radio altitude less than 100 feet and autopilot
engaged. However, if EFS is active when descending through 100 feet RA, it
remains active until AOA is reduced below approximately stick shaker threshold.
There are no flight deck indications that the system is properly armed or activated.
As airspeed decreases towards stall speed with flaps down, the Speed Trim System
uses the Speed Trim function to trim the stabilizer nose down above stick shaker
AOA. With flaps up, as AOA approaches stick shaker, the stabilizer nose down
trim commands transition from the Speed Trim function to the MCAS function.
These trim schedules produce a predictable and increasing column force with
increasing aft column displacement. With the column aft, the amount of column
force increase is more pronounced with the onset of EFS.
Flight Control Computer Monitors
The Flight Control Computers contain monitors which provide protection against
possible runaway stabilizer conditions caused by erroneous FCC stabilizer trim
commands. The FCCs continuously monitor each other’s stabilizer trim
commands, and in the event an erroneous command is detected, stabilizer trim
commands, autopilot trim commands, and CWS trim commands are stopped and
inhibited for the remainder of the flight for that FCC. These trim commands are
then provided by the other FCC. In addition, main electric stabilizer trim remains
available.
Autopilot Elevator Monitor
The Autopilot Elevator Monitor protects against erroneous elevator commands
that can result in erroneous autopilot stabilizer trim commands. The Autopilot
Elevator Monitor is available when:
• Autopilot is engaged, in single channel, and
• Pitch mode is other than G/S or G/P, and
• Flaps are 15 or less.
March 1, 2021
