737 Flight Crew Operations Manual
Flight Controls -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
9.20.12 D6-27370-866-EGP
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.
YK981 - YK992
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. Only main yaw damper inputs are shown on the yaw damper indicator.
Main and standby yaw damper inputs to the rudder are shown on the RUDDER
display of the flight control surface position indicator. The pilot can override
either main or standby yaw damper inputs using either the rudder pedals or trim
inputs.
YK993 - YW274
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. Main and standby yaw damper inputs to the rudder are shown on the
RUDDER display of the flight control surface position indicator. 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.
September 15, 2016
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