The rudder provides yaw control
about the airplane’s vertical axis.

The A and B FLT CONTROL switches
control hydraulic shutoff valves for the
rudder and the standby rudder.
  • Each set of rudder pedals is
    mechanically connected by
    cables to the input levers of
    the main and standby rudder
    PCUs.
At speeds above approximately 135 kts, both hydraulic system
A and B pressure are each reduced within the main PCU by
approximately 25% each. This function limits full rudder
authority in flight after takeoff and before landing.
Flight Controls SGR
B737-700/800/900  Flight Controls - Yaw Control