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AILERON AND FLAPERON CONTROL -FLAPERON PCU -FUNCTIONAL DESCRIPTION
Indications
The EICAS status message ACTUATOR PRESS SNSR shows when the differential pressure sensor on one of the flaperon PCUs is defective. The rudder also uses the same message.
The status message FLIGHT CONTROL SYS shows on the status display when one or more flaperon actuator is failed or the actuator confidence test has failed.
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AILERON AND FLAPERON CONTROL -FLAPERON PCU -FUNCTIONAL DESCRIPTION
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777 AIRCRAFT MAINTENANCE MANUAL
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AILERON AND FLAPERON CONTROL -AILERON AND FLAPERON PCU -PCU MODES
General
The PFCs and the ACEs control the mode of operation of the aileron PCUs. The ACEs control the bypass solenoid of the PCUs. The PFC sends commands to the ACEs to control the blocking solenoids in all three PFCS modes.
The ACEs control the mode of operation of the flaperon PCUs.
Aileron PCU Modes
The aileron PCU has three modes:
*
Normal
*
Bypass
*
Blocking/Damped.
The aileron PCU is in the normal mode when there is no failure in the PCU and there is no failure in its on-side ACE. In the normal mode, the ACE energizes the bypass and blocking solenoids below cruise speed. At or above cruise speed, the ailerons are locked out. The ACEs keep the bypass solenoid energized but the PFCs send a command to de-energize the blocking solenoid on all the PCUs. The PCUs are still in the normal mode.
The aileron PCU is in the bypass mode when there is an electrical or hydraulic failure with the PCU or its ACE during flight below cruise speed. The ACE then de-energizes the bypass solenoid. The adjacent PCU, still in the normal mode, moves the aileron and backdrives the failed PCU. If both PCUs on the same aileron are in the bypass mode during flight, the aerodynamic lift moves the aileron trailing edge by about 15 degrees up from the faired position.
The aileron PCU is in the blocking/damped mode when there is a failure with the PCU or its ACE during flight at or above cruise speed. The ACE de-energizes the bypass solenoid of the PCU. The aileron lock out function of the PFC causes the ACEs to de-energize the blocking solenoid of all the PCUs. Under these conditions, the failed PCU is in the blocking/damped mode while the other PCUs are locked out in the normal mode. If both PCUs on the same aileron are in the blocking/damped mode, the aerodynamic lift cannot move the aileron up.
If there is a loss of the center and left hydraulic system power during the time the ailerons are locked out, the PFCs send a command signal to the ACEs to keep the blocking solenoids de-energized. All the ailerons PCUs stay in the blocking/damped mode. This prevents the sudden aileron upfloat and undesired roll of the airplane when the ailerons unlock later in the flight.
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AILERON AND FLAPERON CONTROL -AILERON AND FLAPERON PCU -PCU MODES
On the ground, with no electrical or hydraulic power on the aileron PCUs, the PCUs are in the blocking/damped mode. The aileron cannot move up but it can move down with an outside force.
Flaperon PCU Modes
The flaperon PCUs operate in two modes:
*
Normal
*
Bypass.
The flaperon PCU is in the normal mode when there is no failure in the PCU or its ACE. The ACE then energizes the bypass solenoid.
The flaperon PCU is in the bypass mode when there is an electrical or hydraulic failure with the PCU or its ACE. The ACE then de-energizes the bypass solenoid. If both PCUs on a flaperon are in the bypass mode, the flaperon can move freely. In flight, the aerodynamic lift then causes the flaperon to move 10 degrees up from the faired position.
When the airplane is on the ground with airspeed less than 85 knots and at least one engine running near takeoff thrust, the flaperon bypass logic of the PFC normal mode operates. This function sends a command signal to the ACEs to put all the flaperon PCUs in the bypass mode. At low airspeed, the weight of the flaperon causes the flaperons to droop. Also, the flaperons can possibly flutter. As the airspeed increases, the airloads gradually float the flaperons to the neutral position.
When the airspeed is approximately 100 knots, the PFCs send a command signal to the ACEs to put all the flaperon PCUs in the normal mode. The PFCs then send commands to the ACEs to gradually move the flaperons to the drooped position.
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