737 MAX Flight Crew Operations Manual
Flight Controls -
System Description
9.20.8
MN-FLT-OH-201
Control column actuated stabilizer trim cutout switches interrupts operation of
main electric stabilizer trim, autopilot trim and the Speed Trim function when the
control column movement opposes trim direction. Aft control column movement
does not interrupt Maneuvering Characteristics Augmentation System (MCAS)
nose down trim commands. Forward control column movement interrupts MCAS
nose up trim commands.
In addition to the control column actuated stabilizer trim cutout switches, the FCC
contains a software column cutout function which adds a layer of redundancy to
mitigate a latent failure of the column cutout switches. The control column cutout
function interrupts operation of autopilot trim and the Speed Trim function when
the control column movement opposes trim direction. Aft control column
movement does not interrupt MCAS nose down trim commands. Forward control
column movement interrupts MCAS nose up trim commands. The software
column cutout function cuts out automatic stabilizer commands beyond the cutout
position of the control column actuated stabilizer trim cutout switches. Main
electric stabilizer trim commands are not inhibited.
When the STAB TRIM override switch is positioned to OVRD, main electric
stabilizer trim can be used regardless of control column position.
Manual stabilizer control is accomplished through cables which allow the pilot to
position the stabilizer by rotating the stabilizer trim wheels. The stabilizer is held
in position by two independent brake systems. Manual rotation of the trim wheels
can be used to set the desired stabilizer position, after the STAB TRIM cutout
switches have been placed in the CUTOUT position. The effort required to
manually rotate the stabilizer trim wheels may be higher under certain flight
conditions such as at high airspeeds. Grasping the stabilizer trim wheel will stop
stabilizer motion.
Stabilizer Trim Operation with Forward or Aft CG
In the event the stabilizer is trimmed to the end of the electrical trim limits,
additional trim is available through the use of the manual trim wheels. If manual
trim is used to position the stabilizer beyond the electrical trim limits, the stabilizer
trim switches may be used to return the stabilizer to electrical trim limits.
Stabilizer Position Indication and Green Band
Stabilizer position is displayed in units on two STAB TRIM indicators located
inboard of each stabilizer trim wheel. The STAB TRIM indicators also display the
TAKEOFF green band indication.
March 1, 2021
