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FSEU -flap/slat electronics unit

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GSE -ground support equipment

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HLCS -high lift control system

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LRU -line replaceable unit

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LVDT -linear variable differential transformer

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MEC -main equipment center

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MFD -multi-function display

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PCU -power control unit

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PFC -primary flight computer

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PFCS -primary flight control system

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PFD -primary flight display

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PSAS -pitch stability augmentation system

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PSEU -proximity sensor electronic unit

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RVDT -rotary variable differential transformer

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SAARU -secondary attitude air data reference unit

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TAC -thrust asymmetry compensation

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WEU -warning electronic unit

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WOW -weight-on-wheels

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777 AIRCRAFT MAINTENANCE MANUAL

RUDDER CONTROL -INTRODUCTION

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777 AIRCRAFT MAINTENANCE MANUAL

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RUDDER CONTROL-GENERAL DESCRIPTION

General

The pilots manually command the rudder; the autopilot automatically commands it.
Manual Operation -Rudder Pedals

The flight crew uses two conventional rudder pedals to control yaw.
Four rudder pedal position transducers change the flight crew rudder pedal commands to analog electrical signals. These signals go to the four actuator control electronics (ACEs). The ACEs change the signals to digital format and send them to the three primary flight computers (PFCs) through the flight controls ARINC 629 buses.
The PFCs use position data from the rudder pedals, data from the air data inertial reference unit (ADIRU) and the airplane information management system (AIMS), to calculate control surface commands. The PFCs send the digital commands to the ACEs, which change them to analog signals. The ACEs send the analog position commands to the power control units (PCUs), which move the rudder. The position transducers on the PCU actuator pistons supply position feedback to the ACEs.
Two gust suppression pressure transducers measure wind gusts on the vertical stabilizer. The transducer signals go to the ACEs and then to the PFCs through the flight controls ARINC 629 buses. The PFCs command the rudder PCUs to move. This movement of the rudder reduces the effect of the side gust.
Two modal accelerometers measure the lateral movement of the aft fuselage. The accelerometer signals go to the ACEs and then to the PFCs through the flight control ARINC 629 buses. The PFCs calculate command signals for the ACEs to move the rudder PCUs to decrease the lateral movement of the forward and aft cabin.
The PFCs operate the yaw damper and rudder ratio functions.
Manual Operation -Rudder Trim
The rudder trim control, on the aisle stand, and the trim actuator let the flight crew trim out unwanted rudder pedal forces. When the pilots move the rudder trim control, the switch sends a signal to the ACEs and the PFCs. The PFCs and the ACEs command the rudder trim actuator to move the rudder pedals and the position transducers through the feel and centering mechanism. The rudder pedal position transducers send a signal to the ACEs and PFCs to move the rudder.

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RUDDER CONTROL-GENERAL DESCRIPTION

The rudder trim indicator, also on the aisle stand, shows the position of the rudder trim. The rudder trim actuator position transducer sends a feedback signal to the ACEs and the PFCs. The PFCs then command the trim indicator through AIMS.
The rudder manual trim cancel switch, on the aisle stand, sends a signal to the ACEs and the PFCs to command the rudder trim to zero.
When the thrust asymmetry compensation (TAC) switch on the P5 panel is in the AUTO position, the PFCs automatically control the rudder trim. This control is to make allowance for asymmetrical thrust from the engines. The TAC function does not operate when the TAC switch is in the OFF position. The manual trim cancel switch does not remove any rudder trim caused by TAC.
Autopilot Operation

When autoland is active, the autopilot flight director computers (AFDCs) control the yaw attitude of the airplane for crosswind and engine-out conditions. The AFDCs supply yaw commands to the PFCs through the flight controls ARINC 629 buses. The PFCs use these inputs to calculate position commands for the rudder.
The PFCs also calculate rudder pedal backdrive commands. The PFCs send these commands to the AFDCs, which transmit rudder movement commands to the backdrive actuators. The backdrive actuators move the rudder pedals to a position to match the autopilot rudder command.
　
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