*
Secondary yaw damper function

*
Force fight equalization.

The PFC does not control the pressure reducer solenoid in the secondary mode. The ACE has a hydraulic pressure control which does this function.
No other rudder function is available in secondary mode.
Degraded Rudder Ratio Schedule

The PFCs receive rudder control command signals from the rudder pedal position transducers. The degraded rudder ratio receives the flaps and slats retracted discrete signal from the ACEs. The degraded rudder ratio function calculates the rudder command from the rudder pedal position transducers for two fixed ratios. When the flaps and slats are not retracted, the ratio is high. When the flaps and slats are retracted, the ratio is low.
Secondary Yaw Damper Function

The PFC has a degraded yaw damper function in secondary mode. It uses available air and inertial data to supply rudder commands.
If some of the air or inertial data is not available, the function filters the yaw damper rate and reduces its gain.
Force Fight Equalization
The rudder commands go to the force fight equalization function. The PFCs use rudder PCU differential pressure data from the ACEs to equalize all the rudder PCU commands. This function keeps rudder PCU force fight to a minimum.

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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -SECONDARY MODE

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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -DIRECT MODE

General

In direct mode operation of the PFCS, the ACEs calculate rudder control commands based on these inputs:
*
Degraded rudder ratio schedule

*
Hydraulic pressure control

*
Failure monitor.

Degraded Rudder Ratio

The ACEs receive yaw command signals from the rudder pedal position transducers. The degraded rudder ratio receives the flaps and slats retracted discrete signal from the FSEUs. The degraded rudder ratio function calculates the rudder command from the rudder pedal position transducers for two fixed ratios. When the flaps and slats are not retracted, the ratio is high. When the flaps and slats are retracted, the ratio is low.
Hydraulic Pressure Control

When the PFCS is in direct or secondary mode and all ACEs are operational, the ACEs reduce the hydraulic pressure of their assigned PCU.
If there is an electrical power loss to an ACE or failure of an ACE or PCU, the pressure reducer solenoid of the PCU de-energizes. The PCU then operates at high pressure to supply enough force for the control of the rudder.
Failure Monitor
The failure monitor controls the signals to the bypass and the damped solenoids of the applicable PCUs. When it finds a single failure of the ACE or its on-side PCU, the ACE de-energizes the bypass solenoid of its on-side PCU and the damped solenoid of its adjacent PCU.
The ACE failure monitor also controls the pressure reducer solenoid of the adjacent PCU through the hydraulic pressure control function.
The failure monitor operates in all three modes, normal, secondary, and direct. The failure monitor can find faults in these:
*
ACE

*
PCUs

*
Pedal position transducers

*
Interface wiring.

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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -DIRECT MODE

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RUDDER CONTROL -FUNCTIONAL DESCRIPTION -RUDDER TRIM

General

The rudder trim selector and the manual trim cancel switch send discrete electrical signals to the L1 ACE and the R ACE. The ACEs transmit these signals to the PFCs via the flight controls ARINC 629 buses.
The L1 and R ACEs, and the PFCs operate the rudder trim function as a two channel system. The L1 ACE supplies rudder trim actuator engagement, manual trim cancel, and servo loop control. The R ACE supplies rudder trim actuator engagement, rate discrete, arm, and brake status control.
In normal mode, when the thrust asymmetry compensation (TAC) function is active, the PFCs control the rudder trim actuator through the L1 and R ACEs based on differential engine thrust.
During normal and secondary modes of operation, the PFCs use pilot inputs from the rudder trim selector and the manual trim cancel switch to control the rudder trim actuator at one of two available speeds. The PFCs transmit commands back to the ACEs which then control the rudder trim actuator.
During direct mode of operation, the ACEs use the requests from the rudder trim selector and directly command the rudder trim actuator at a single speed.
　
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