(a)  
The EICAS caution message FLAPS PRIMARY is displayed when one or more flap groups enter primary electric mode due to a disagree.

 (b)  
The EICAS caution message FLAPS DRIVE is displayed when one or more flap groups fail to move in primary electric mode due to a disagree or a shutdown.

 (c)  
The EICAS status message TE FLAPS appears when hydraulic TE flap operation has failed, or when there is a flap asymmetry.

 (d)  
The EICAS status message LE SINGLE DRIVE is displayed when there is a single Leading Edge Drive Mode failure. The status message LE MULT DRIVE is displayed when there are multiple Leading Edge Drive Mode failures on one or more drive units. A mode is either Primary Pneumatic or Primary Electric operation.

 (e)  
The EICAS status message FLAP SYS MONITOR is displayed when there is a failure of a LE flap power drive unit limit switch, TE flap position RVDT transmitter, or flap lever RVDT.

 (f)  
The EICAS status message FLAP CONTROL L, FLAP CONTROL C, or FLAP CONTROL R is displayed when there is a failure of the corresponding flap control unit. The EICAS caution message FLAPS CONTROL is displayed when there is a failure of all three flap control units, or if the ALTN FLAPS ARM switch is pressed to the ARM position.

 B.
Functional Description - LE Flap Drive Train and Load Relief

 (1)  
Each PDU mechanically positions a set of flaps (Fig. 2). The eleven variable camber flaps in each wing are positioned through torque tubes, rotary actuators and flap actuating linkages. The three Krueger flaps in each wing are positioned through offset gearboxes, drive shafts, rotary actuators and flap actuating linkages.

 (2)  
In primary pneumatic mode, the FCU activates relays which operate the PDU's. This opens the primary drive (normally-closed) solenoid valve which supplies air simultaneously through a filter and alternate solenoid valve to the inlet of the butterfly regulator valve actuator and to the pneumatic motor brake, causing the brake to be released. A bleed-off reference regulator limits the pressure supplied to the butterfly regulator valve actuator.

 (3)  
The electrical signal also energizes the 400-Hz directional control servomotor and starts rotation of the primary controller in the extend (or retract) direction. This motion is transmitted to the summing differential which opens the rotary control valve in the direction to extend (or retract) the flaps. As the valve opens, air is admitted to the pneumatic motor causing it to rotate in the requested direction. The resulting rotation is transmitted through reduction gearing to the output shaft of the PDU.

 (4)  
The output shaft rotation is transmitted back to the summing differential. If this feedback rotational velocity is greater than the rotational velocity of the 400-Hz servo control motor, the summing differential output will partially close the rotary control valve, slowing down the pneumatic motor until the two inputs to the differential - the servomotor speed and the output shaft feedback speed - are equal.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

 (5)  
As the output shaft starts to move in the extend (or retract) direction, a translating nut in the primary controller starts to move along the controller shaft from its initial position at one end of the housing to the opposite end of the controller. Dog stops on the translating nut engage mating stops tied to the controller housing.

 (6)  
The flaps are stopped at the desired angle of extension by the stroke of the flap PDU's. When the translating nut within the primary controller has reached the end of stroke and engaged the dog stops tied to the controller housing, the servomotor is stalled and the output of the summing differential closes the rotary control valve, shutting off the air supply to the pneumatic motor. After an FCU-controlled time delay, the servomotor is de-energized and the normally-closed solenoid valve closes, venting the pneumatic brake and allowing it to engage and prevent motion of the output shaft.

 (7)  
The PDU can be reversed at any point within its normal travel. The stopping and reversal of the primary controller will result in a reverse servo control input, creating reversal of the rotary valve, the pneumatic motor, and in turn, the output shaft.
　
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