737 MAX Flight Crew Operations Manual
Flight Controls -
System Description
9.20.16
MN-FLT-OH-201
Rudder Trim
The RUDDER trim control, located on the aft electronic panel, electrically
repositions the rudder feel and centering unit which adjusts the rudder neutral
position. The rudder pedals are displaced proportionately. The RUDDER TRIM
indicator displays the rudder trim position in units.
Yaw Damper
The yaw damper system consists of a main and standby yaw damper. Both yaw
dampers are controlled through Stall Management/Yaw Damper (SMYD)
computers. The SMYD computers receive inputs from both ADIRUs, both control
wheels and the YAW DAMPER switch. SMYDs provide yaw damper inputs to the
main rudder Power Control Unit (PCU) or standby rudder PCU, as appropriate.
Either yaw damper is capable of providing dutch roll prevention, gust damping
and turn coordination. Yaw damper operation does not result in rudder pedal
movement. The pilot can override either main or standby yaw damper inputs using
either the rudder pedals or trim inputs.
During normal operation the main yaw damper uses hydraulic system B and the
SMYD computers provide continuous system monitoring. The YAW DAMPER
Switch automatically moves to OFF, the amber YAW DAMPER light illuminates
and the YAW DAMPER switch cannot be reset to ON when any of the following
conditions occur:
• SMYD senses a yaw damper system fault,
• SMYD senses that the yaw damper does not respond to a command,
• B FLT CONTROL switch is positioned to OFF or STBY RUD.
During manual reversion flight (loss of hydraulic system A and B pressure), both
FLT CONTROL switches are positioned to STBY RUD. In this case, the YAW
DAMPER switch can be reset to ON and the standby hydraulic system powers the
standby yaw damper. During Standby Yaw Damper operation, movement of the
control wheel sends a signal to the standby rudder PCU to move the rudder. This
gives rudder assist to help turn the airplane when control of the ailerons is through
manual reversion.
March 1, 2021
