E.  
In primary hydraulic mode, the priority of FCU in control of a group of flaps is the left FCU initially, then the center, and lastly the right following successive FCU failures. In primary electric mode, the priority of FCU in control for a group of flaps is the right FCU initially, then the center, and lastly the left following successive FCU failures.

 F.  
Each FCU continuously provides flap system failure protection while operating in the primary hydraulic mode or the primary electric mode.

 (1)  
System failure protection includes asymmetry detection, uncommanded motion detection, flaps-moving-away detection, and primary hydraulic and primary electric disable functions. Protection is provided separately for inboard and outboard TE flaps.

 (2)  
Each FCU will disable its control outputs if it determines that a flap asymmetry condition exists. The FCU's will disable their control and failure protection functions when the alternate system is engaged, but will continue to provide position information for flight deck displays and user systems.

 G.  
The flap control units automatically retract the TE flaps to relieve aerodynamic loads on the flaps if they are extended at an excessive airspeed. Load relief is activated based on flap position and on airspeed data supplied by the air data computers.

 H.  
BITE

 (1)  
Each FCU automatically runs a power-up test for approximately 2 seconds each time power is applied.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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MAINTENANCE MANUAL

 (2)  
Each FCU independently runs a continuous built-in test to monitor for failures of internal components and FCU inputs and interfaces.

 (3)  
A ground functional test may be initiated by the Central Maintenance Computer System while the airplane is on the ground. This test commands each FCU to check all LRU's for open/short circuits or failures, to check for subsystem power, to check ARINC 429 data busses for correct data format, and to check system discrete inputs. Faults internal to the FCU's are stored as shop faults.

 4.  Input Lever Assembly and Flap Actuator (Fig. 2)
______________________________________
 A.  The input lever assembly located on the left body gear wheel well forward bulkhead houses the flap actuator, the input lever, and the rods which link to the input crank on each power package.
 B.  The flap actuator is a linear actuator which drives its output shaft out or in to change flap position on command from the FCU's. The actuator contains a 115 volt ac reversible motor, a solenoid operated brake, gearing, and an RVDT position transmitter. The solenoid brake is released whenever an extend or retract command is received from the FCU's.
 5.  Flap Power Packages (Fig. 2)
___________________
 A.  The TE flap power packages receive mechanical input from the input lever assembly or electrical input from the FCU's or the alternate flaps system relays. The inboard flaps power package is located on the forward bulkhead of the left body gear wheel well and the outboard flaps power package is located on the forward bulkhead of the right body gear wheel well. Each power package consists of a flap control assembly, a hydraulic motor, an alternate electric motor, and a flap power unit (gearbox).
 B.  Flap Control Assembly
 (1)  
The flap control assembly houses the flap control module, the RVDT position transmitter, the power package limit switch pack, and the follow-up feedback mechanism.

 (2)  
Flap Control Module (Fig. 4)

 (a)  
The flap control module receives and regulates the hydraulic fluid flow to the hydraulic motor. The module consists of a control valve, a priority and flow control valve, a motor-operated bypass valve, and a check valve.

 (b)  
Flap Control Valve

 1)  The flap control valve is a mechanically operated spool valve used to control directional flow of hydraulic fluid to the flap hydraulic motor. The valve is a cartridge type unit which mounts on the control module. The valve is mechanically driven by the flap control linkage. The valve may be removed as a unit only after the control module has been removed from the airplane.
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