*
ILS course.
Runway Alignment
The AFDC calculates the roll command and yaw command for the runway alignment modes.
The AFDC uses ILS course and airplane heading inputs to calculate the yaw control command and the roll command.
Rollout
The AFDC calculates the yaw command for the rollout mode.
The AFDC uses these inputs to calculate the rudder surface command for yaw control:
*
Localizer deviation
*
Localizer deviation rate
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AFDS -FUNCTIONAL DESCRIPTION -ROLL AND YAW CONTROL
* Rudder position.
It also calculates a roll command for flight director (F/D) display during ground rollout. The flight crew uses the F/D rollout display to control the rudder pedals after the airplane has landed.
Roll Flight Director
The AFDC uses the roll command or LNAV steering command and roll attitude to calculate the roll F/D signal. The F/D then formats the signal and sends it to AIMS.
Roll Command Calculations and Limiting
The AFDC uses these to calculate the roll command and turn compensation signal:
*
LNAV steering command
*
Roll command
*
Roll attitude
*
Roll rate.
The AFDC limits the bank angle during autopilot and bank angle protection (BAP) operations. The AFDC sends the roll command to the PFCs and the turn compensation signal to the yaw command and the pitch F/D calculations.
Yaw Command Calculations and Limiting
The AFDC uses these inputs to calculate the rudder command:
*
Turn compensation
*
Yaw command
*
Yaw rate.
The AFDC limits the rudder command for the selected mode and sends it to the PFCs.
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AFDS -FUNCTIONAL DESCRIPTION -BACKDRIVE CONTROLS
General
The AFDC backdrive control laws use PFC backdrive commands to supply these commands:
*
Control column
*
Control wheel
*
Control pedal.
Control Column Backdrive
The A and B processors use these signals to supply the control column backdrive command:
*
PFC autopilot engage
*
PFC column backdrive command
*
Column position
*
Column tachometer (TACH) feedback A or B.
Control Wheel Backdrive
The A and B processors use these signals to supply the control wheel backdrive command for autopilot operation:
*
PFC autopilot engage
*
PFC wheel backdrive command
*
Wheel position
*
Wheel TACH feedback A or B.
The A and B processors use these signals to supply the control wheel backdrive command for bank angle protection (BAP) operation:
*
PFC engage wheel backdrive
*
PFC wheel torque command
*
Wheel position
*
Wheel TACH feedback A or B.
In BAP operation, the PFC sends a wheel torque limit command to the AFDC. This will let the flight crew override the backdrive actuator if necessary.
Control Pedal Backdrive
The A and B processors use these signals to supply the control pedal backdrive command:
*
PFC Autopilot engage
*
PFC Yaw engage
*
PFC pedal backdrive command
*
Pedal position
*
Pedal backdrive actuator tachometer (TACH) feedback A or
B.
Backdrive Power Supplies
Each processor sends a backdrive command to a backdrive power supply. Two power supplies, one A and one B, are necessary to drive the motor in each backdrive actuator. This supplies a push-pull drive signal to the actuator motor.
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AFDS -FUNCTIONAL DESCRIPTION -ENGAGE INTERLOCKS INTRODUCTION
Purpose
The autopilot engage interlock circuits in the AFDCs and PFCs monitor the operation, power, and components of the AFDS and PFCS. With normal conditions, the circuits let the autopilot engage. If conditions are not normal, the autopilot disengages or the autopilot does not engage.
Mode Control Panel
The autopilot engage switches are on the MCP. The flight crew pushes either switch to engage the autopilot.
Usually, all three AFDCs engage when the flight crew pushes either A/P engage switch. If there are faults, it is possible to engage one or two AFDCs. Autoland requires two or three AFDCs engaged.
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