RUDDER CONTROL -FUNCTIONAL DESCRIPTION -THRUST ASYMMETRY COMPENSATION
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ELEVATOR CONTROL -INTRODUCTION
General
The elevators supply short-term correction of the pitch attitude of the airplane. This movement is around the lateral axis of the airplane.
There is one elevator panel on each side of the aft fuselage. Hinges attach the elevator to the rear spar of the horizontal stabilizer. Two hydraulic power units move each elevator panel.
Pitch Control
The pilots manually command pitch correction with forward and aft movement of the control column.
When engaged, the autopilot automatically commands the elevators. During autopilot operation, actuators backdrive the control columns.
Elevator Off-load Function
The elevator off-load function transfers manual and autopilot commanded elevator deflection to the stabilizer. The stabilizer movement allows the elevators to move to the neutral position.
Abbreviations and Acronyms
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ACE -actuator control electronics
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ADIRS -air data inertial reference system
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ADIRU -air data inertial reference unit
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AFDC -autopilot flight director computer
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AFDS -autopilot flight director system
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AIMS -airplane information management system
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AOA -angle of attack
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ARINC -Aeronautical Radio, Incorporated.
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CMCS -central maintenance computing system
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CPU -central processing unit
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EHSV -electrohydraulic servo valve
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EICAS -engine indication and crew alerting system
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FSEU -flap/slat electronics unit
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LIB -left inboard
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LOB -left outboard
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LVDT -linear variable differential transformer
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MAT -maintenance access terminal
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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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RIB -right inboard
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ROB -right outboard
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SAARU -secondary attitude and air data reference unit
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TED -trailing edge down
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TEU -trailing edge up
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ELEVATOR CONTROL -INTRODUCTION
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ELEVATOR CONTROL -GENERAL DESCRIPTION
General
The pilots manually command the elevators and the autopilot automatically commands them.
Manual Operation
The flight crew uses two conventional control columns to command pitch. They connect to torque tubes joined by a break-out mechanism. This allows one control column to move if the other jams.
The flight crew can make manual commands to the elevator in the normal mode with the pitch trim switches. This is possible only if the airplane is in the air.
Six position transducers change flight crew control column commands to analog electrical signals. These signals go to the four actuator control electronics (ACEs) that change the signal to digital format. The digital signals go to the primary flight computers (PFCs) through the ARINC 629 buses.
The PFCs use data from these sources to calculate control surface commands:
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Column position
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Air data inertial reference unit (ADIRU)
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Airplane information management system (AIMS).
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The PFCs send digital commands to the ACEs, which change them to analog signals. The ACEs then send the analog surface position commands to the power control units (PCUs). The PCUs move the elevators. The position transducers on the PCU hydraulic pistons send actuator position feedback to the PFCs through the ACEs.
The PFCs use data from the ADIRU to calculate elevator feel commands. The feel command goes through the ACE to the left and right feel actuators on the elevator feel units. The feel actuators supply to the column a variable feel based on airspeed.
The ACEs get analog signals from the force transducers and send them to the PFCs. The PFCs use these signals to verify control column null position.
Autopilot Operation
When engaged, the autopilot flight director computers (AFDCs) control airplane pitch. The AFDCs supply pitch commands to the PFCs through the flight controls ARINC 629 buses. The PFCs process these commands to supply position commands for the elevators. These position commands go through the ACEs to the PCUs.
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