*
Roll/Yaw control laws

*
Backdrive command section.

Pitch Control Laws
The pitch control laws calculate part of the pitch command and send it to the primary flight computers (PFCs). The PFCs accept the pitch command only when the primary flight control system (PFCS) mode is NORMAL. If the PFCS mode is SECONDARY or DIRECT, the PFCs do not permit the autopilot to engage. The PFCs use this command to calculate a surface command that goes to the actuator control electronics (ACEs).
The ACEs change the PFCs surface commands to analog signals and send them to the power control units (PCUs). The PCUs move the flight control surfaces. The surface position transducers in the PCUs send surface position to the ACEs. The ACEs send the surface position to the PFCs. This position feedback completes the PFCs control loop. The AFDCs control loop closes when the AFDCs sense the airplane attitude and performance changes to match the initial AFDC pitch command.
Roll/Yaw Control Laws
The roll/yaw control laws calculate the roll and yaw commands and sends them to the PFCs. The PFCs accept the roll and yaw commands only when the PFCS mode is NORMAL. If the PFCS mode is SECONDARY or DIRECT, the PFCs do not permit the autopilot to engage. The PFCs change the roll and yaw commands to surface commands. The surface commands go to the ACEs.
The ACEs change the PFCs surface commands to analog signals and send them to the PCUs. The PCUs move the flight control surfaces. The surface position transducers in the PCUs send surface position to the ACEs. The ACEs send the surface position to the PFCs. This position feedback completes the PFCs control loop. The AFDCs control loop closes when the AFDCs sense the airplane attitude and performance changes to match the initial AFDC roll/yaw command.
Backdrive Command Section
The backdrive command section calculates the control column, control wheel, and rudder pedal backdrive actuator drive signals. The AFDCs operate the backdrive actuators during:
*
Autopilot operations

*
Bank angle protection (control wheel backdrive actuators only).

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AFDS -FUNCTIONAL DESCRIPTION -AUTOPILOT CONTROLS

During autopilot operations, the PFCs use the AFDC pitch and roll/yaw control law commands to calculate backdrive commands. The backdrive commands go to the AFDCs. The AFDCs change the commands to actuator drive signals and send them to the backdrive actuators.
For bank angle protection (BAP), the PFCs monitor manual bank angle commands. If the flight crew banks the airplane more than 35 degrees, the PFCs send a control wheel engage signal to the AFDC. The PFCs also send control wheel backdrive commands that are opposite to the flight crew input. The AFDCs change the control wheel commands to actuator drive signals and send them to the control wheel backdrive actuators. The control wheel backdrive actuators move the control wheel to roll the airplane to a roll attitude less than 30 degrees. The control wheel position transducers send the control wheel position to the ACEs. The ACEs digitize the control wheel position and send it to the PFCs. The PFCs convert the control wheel position to a surface command (aileron/flaperon). The PFCs send the surface command to the ACEs. The ACEs send the surface command to the PCUs. The PCUs move the surfaces. The surface position transducers supply surface position to the ACEs. The ACEs send the surface position to the PFCs. This closes the PFCs control loop. The pilot can override the control wheel backdrive actuators with more force to the control wheel. The PFCs use signals from a control wheel force transducer to detect a pilot override.
BAP operates with the autopilot engaged or disengaged. If the autopilot is engaged when BAP is active, the AFDCs make an autopilot caution EICAS message and a roll mode failure shows on the PFD.
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AFDS -FUNCTIONAL DESCRIPTION -FLIGHT DIRECTOR CONTROL

General
The AFDC sends pitch and roll control law data to the flight director program. The program calculates this display data:
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Pitch flight director bar

*
Roll flight director bar.

The AFDC sends the display data to the AIMS cabinets.
An AFDC failure can cause the loss of one or both flight director bars.
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AFDS -FUNCTIONAL DESCRIPTION -FLIGHT DIRECTOR CONTROL

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