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HIGH LIFT CONTROL -GENERAL DESCRIPTION
Secondary Mode
In the secondary mode, the FSEUs receive input signals from the flap lever position sensor. The FSEUs then energize secondary/alternate control relays. These relays energize bypass solenoids in the primary control valves to stop hydraulic power to the hydraulic motors. These relays also control electrical power to the flap and slat electric motors in the PDUs. The electric motors then move the flap and slat mechanisms.
As the flaps and slats move, position sensors send a position feedback signal to the FSEUs. The FSEUs command the relays to stop the electric motors when the flaps and slats are at the commanded position.
The secondary mode also uses the flap and slat skew sensors. If the flaps are out of alignment, the FSEUs prohibit movement of the flaps in the secondary mode. This is also true for the slats.
Alternate Mode
The pilots manually control the alternate mode with the switches on the alternate flaps panel. The arm switch on this panel sends a discrete to the FSEUs to disengage the primary and secondary modes. This switch also energizes two of the secondary/alternate control relays. These two relays energize bypass solenoids in the primary control valves to stop hydraulic power to the hydraulic motors. The primary control valves also create a hydraulic loop to permit the hydraulic motors to be backdriven.
The alternate flaps selector sends commands through limit switches to energize the other secondary/alternate control relays. These relays control electrical power to the flap and slat electric motors on the PDUs. The limit switches remove electrical power from these relays when the flaps and slats are at their limits.
The electric motors then move the flap and slat mechanisms. The flaps and slats move until the pilot moves the alternate flaps selector to OFF, or the flaps and slats are at their limits.
The alternate mode control does not use the flap and slat position sensors or skew sensors. But, the FSEUs continue to receive signals from these sensors for EICAS messages and position indication.
EFFECTIVITY BEJ ALL 27-03-00
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777 AIRCRAFT MAINTENANCE MANUAL
HIGH LIFT CONTROL -GENERAL DESCRIPTION
EFFECTIVITY BEJ ALL 27-03-00
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HIGH LIFT CONTROL -INTERFACES -SYSTEM REDUNDANCY
General
The HLCS has two identical lanes for the primary mode and the secondary mode. One lane has control of the HLCS. The other lane monitors the HLCS. The FSEUs automatically transfer control to the other lane after a post-flight self test of the FSEUs or after disengagement from the alternate mode. The FSEUs also switch control to the other lane if:
*
A component fails in the control lane
*
The command and feedback disagree.
Each lane has these components:
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An FSEU
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Two RVDTs in the flap lever position sensor
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Flap primary control valve solenoid coils
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Slat primary control valve solenoid coils
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Flap position sensors
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Slat position sensors.
The following components are not in the HLCS lanes:
*
The flap and slat skew sensors
*
The autoslat priority valves
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The secondary/alternate control relays
FSEUs
One FSEU is in each lane. Only the FSEU in the control lane sends the flap and slat commands to the flap and slat primary control valves.
EFFECTIVITY
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Flap Lever Position Sensor
Each lane uses two of the four RVDTs in the flap lever position sensor.
Flap and Slat Primary Control Valve Solenoid Coils
The flap and slat primary control valves have dual-coil solenoids. Each lane controls one of the coils in each solenoid.
Flap and Slat Position Sensors
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