(8)  
When a PDU is not receiving signals from the FCU's, the PDU maintains its LE flaps in a fixed position with the pneumatic motor brake which prevents the output shaft from rotating.

 (9)  
An overpressure switch is installed between the pressure regulator and the rotary control valve. If there is a failure of the pressure regulator, overpressure (>25 psi) will activate the pressure switch which will open the AC return circuit in the PDU, causing the unit to stop short of its required travel. The FCU will switch the flap group to primary electric mode to complete the LE extension or retraction.

 (10)
 In primary pneumatic mode, the LE flaps will automatically retract when the reverse thrust levers are deployed. The reverse thrust levers actuate microswitches which are monitored by the FCU's. The automatic retraction function is armed when the airplane is on the ground.

 (11)
 Group A LE flaps retract when engine 1 and 4 reverse thrust levers are both deployed, or when engine 2 and 3 reverse thrust levers are both deployed. When the reverse thrust levers are stowed, flap re-extension is delayed 6 seconds to allow for engine stabilization.

 (12)
 When the alternate drive motor is energized, its integral brake is released and the alternate solenoid valve is energized to prevent control air from flowing to the pressure regulator and to the brake on the pneumatic motor.

 (13)
 With the pneumatic motor brake thus engaged, the sun gear of the planetary gear system is locked in a fixed position. This allows the electric motor to drive through the annular gear and out through the planet gears to the output shaft, although at reduced speed.

 (14)
 There is a shear section in the gear train at the summing differential which is allowed to rupture, should the translating nut in the primary controller become jammed, to allow the alternate drive system to operate.

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 27-81-00
 ALL  ú ú 01 Page 17 ú Jun 10/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 (15)
 The alternate controller and feedback annunciator unit is equipped with limit switches at both ends of its travel which shut off the alternate drive motor and engage its integral brake at the end of the stroke in either direction.

 C.  
Control

 (1)  
General

 WARNING: ENGINE THRUST REVERSER SLEEVES MOVE TO OPEN POSITION IN
_______ 1-1/2 SECONDS AND CLOSE IN 4-1/2 SECONDS. KEEP ALL PERSONNEL AND EQUIPMENT CLEAR OF TRANSLATION AREA.
 (a)  
For normal mode retraction of the LE flaps, the TE flaps must be operational. Alternate electrical extension is accomplished independent of TE flaps, but the alternate electrical retraction only operate after the inboard TE flaps retracted. The group A LE flaps may be extended and retracted pneumatically using the reverse thrust levers without moving the TE flaps if the TE flaps are extended to or beyond the 5 unit position.

 (b)  
Pneumatic ground power carts may not be capable of supplying sufficient air (3000 CFM and 15 psi minimum) to operate all the LE flaps simultaneously. Therefore, when using pneumatic ground power carts, extend or retract only one group of flaps. Allow the flaps to completely extend or retract and then position the remaining group of flaps.

 (c)  
Pneumatic power will retract the LE flaps in approximately 10 seconds with sufficient force to cause serious injury or damage equipment. The flaps should never be operated without first checking that personnel and equipment are clear of the flaps. During maintenance or servicing, inadvertent operation of the flaps is a potential hazard. To prevent inadvertent operation, safety locks have been provided and should always be installed when personnel are working in or near the LE flap cavity.

 (d)  
The LE flaps may be inadvertently operated in the following ways: 1) With electrical and pneumatic power on the airplane and the

 LE and TE flaps extended, moving the reverse thrust levers will retract and extend the group A LE flaps. No. 1 and 4 or No. 2 and 3 reverse thrust levers operate group A LE flaps.
 2)  With electrical power on the airplane, the TE flaps retracted fully, the LE flaps extended electrically, and the ALTN FLAPS ARM switch is in normal position: pressurizing the pneumatic system will retract the flaps if the application of pneumatic pressure occurs within one minute after operation of the flap control lever.
　
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