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747-400 MAINTENANCE MANUAL
7) CMC DATA FAILURE - The YDM has detected invalid data from the CMC for more than 10 seconds.
8) LEFT/CENTER/RIGHT IRU INTERFACE FAILURE - The YDM has determined the data from an IRU is invalid.
9) IRU COMPARISON FAILURE - The YDM has detected an invalid input from an IRU but is unable to determine which one is at fault.
10) PSM 26 VAC FAILURE UPPER/LOWER - The YDM has detected the loss of or the invalid level of the 26V RMS reference voltage.
11) FWD/AFT ACCELEROMETER UPPER/LOWER YAW DAMPER INTERFACE FAILURE - The YDM has determined an aft/fwd modal suppression accelerometer maintenance fault.
12) ACTUATOR FAILURE UPPER/LOWER - The YDM has detected an actuator maintenance fault.
13) LVDT UPPER/LOWER YAW DAMPER INTERFACE FAILURE - The YDM has detected a LVDT fault.
14) AIR/GROUND COMPARISON FAILURE - The YDM has determined that the two remaining valid air/ground inputs disagree for more than 2 seconds.
15) CHANNEL CODE FAULT - The YDM has detected a channel code fault.
16) INOP INDICATION CIRCUIT FAILURE - The YDM has detected that the INOP light is at fault.
17) UPPER/LOWER RUDDER FAILURE "NO MOVEMENT" - The YDM has determined that there is a ground test rudder position fault.
(5) Vertical Stabilizer
(a) There are two rudder power control modules located on the rear spar of the vertical fin. One controls the upper rudder movements and the other controls the lower rudder movements. The two yaw damper electrohydraulic servos are connected to the mechanical rudder linkage. The mechanical linkage is the interface between the rudder power control modules and the rudder power control actuators, which move the rudders. The upper rudder uses three rudder power control actuators and the lower rudder uses two.
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MAINTENANCE MANUAL
(6)
Rudder Power Control Modules (RPCM)
(a)
The rudder power control module combines the functions of a yaw damper servo with a manually operated hydraulic control valve. Each RPCM (upper and lower) receives inputs from the yaw damper module and the captain. When a RPCM is supplied with either input, it functions to control the output of the hydraulic power cylinders to position the rudders.
(b)
Hydraulic pressure to the rudder power control modules is supplied from multiple independent sources. The system supply pressure is 3000 psi nominally. The pressure may vary from 2000 to 3600 psi. Return pressure is less than 100 psi with possible surges up to 800 psi.
(c)
The module components consist of the input filters, electrohydraulic solenoid and servo valves, yaw damper actuator piston assembly, LVDT, compensator assembly, main control valve, check valve, linkage, and an electrial connector.
(7)
Modal Suppression Accelerometers
(a)
The two forward modal suppression accelerometers are located below the floor in the forward access area E5 (sta 320, LBL/RBL 85, WL 194.68). The two aft modal suppression accelerometers are located below the floor and to the left and right of the area bulk cargo compartment (sta 2260, LBL/RBL 65, WL 194.68).
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