MD-11 Flight Crew Operations Manual
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Flight Controls -
Description and Operation
Flt.10.3
Directional Control System
The directional (yaw) control system consists of an upper and lower rudder, each
having a forward and an aft segment. The aft segment of each rudder is hinged to
the forward segment and is mechanically bused in such a manner that it deflects
in the same direction as the forward segment. The upper rudder is powered by
hydraulic system 1 and the lower rudder is powered by hydraulic system 2. The
full power rudder control system of the MD-11 requires an artificial load feel since
no aerodynamic surface loading is fed back to the pedals.
The rudder mechanical control system is operated with pedals in the cockpit. Each
pair of pedals is independently adjustable for pilot comfort. The rudder pedal
motion is transferred to the rudder actuators by a closed cable system. The rudder
pedals also provide input to the nose wheel steering system for directional control
on the ground.
Non-Reversible Motor Pumps (NRMP), installed in the hydraulic systems,
automatically provide a standby source of hydraulic power to the upper rudder,
stabilizer trim, and lower rudder. A compensator with a low fluid level switch
automatically shuts off hydraulic flow to the motor side of the NRMP if a
compensator low fluid level is detected.
Alerts warn the flight crew when one or both of the NRMPs are inoperative. With
both NRMPs inoperative, rudder standby power is unavailable.
A rudder trim system is installed. Dual yaw damper systems for each rudder
provide turn coordination and damping of dutch roll. The system operates the
rudder hydraulic control valves.
The yaw damper moves the rudder pedals when the autopilot is engaged in
takeoff, go-around, and both SINGLE and DUAL LAND modes. Turn
coordination is always on except during engine-out land mode, engine-out takeoff
mode, engine-out go-around mode, align mode, and rollout mode.
Each Flight Control Computer (FCC) contains two redundant yaw damper control
channels enabling each FCC to be self-monitored and providing four redundant
channels of control. Either FCC provides dual yaw damper function.
Appropriate alerts and overhead panel annunciations warn the flight crew of yaw
damp failures. If a failure is isolated to a single channel, the associated FAIL light
illuminates and an alert is displayed. If the failure cannot be isolated to a single
channel, the FCC fails both channels on the corresponding surface. In this case,
the other FCC maintains dual control. Whenever a channel is selected off, an
appropriate amber alert is displayed. If all channels are selected off, the YAW
DAMP ALL OFF alert is displayed. If all channels have failed the YAW DAMP
ALL FAIL alert is displayed.
October 02, 2006
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