G41425
Leading Edge Flap and Slat Control System Hydraulic Schematic  531 
27-81-0  Figure 4  May 15/71 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

LEADING EDGE FLAPS AND SLATS – TROUBLE SHOOTING
TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Leading edge flaps and slats fail to extend during normal system operation Leading edge flaps and slats fail to extend during alternate system operation Leading edge flaps and slats do not extend or retract at specified trailing edge flap angle   Defective leading edge flap and slat control valve No hydraulic pressure at leading edge standby shutoff valve No dc power leading edge standby shutoff valve Leading edge standby shutoff still in normal (closed) position (Position 1) Leading edge flap and slat control valve out of adjustment  Remove lower pan from flap control unit and disconnect adjustment link from cam follower arm. Manually actuate valve and check leading edge flap operation. If flaps fail to extend -Check that standby hydraulic system low pressure warning light is extinguished. If light is illuminated, refer to Hydraulic System Trouble Shooting, Chapter 29  Remove connector from leading edge standby shutoff valve and check for 28 volts dc. If power is not available check wiring from valve to power source for open circuit Check that FLAP VALVES circuit breaker is closed and that alternate flap master switch is at ARM. Check for power at standby shut-off valve. If power is present valve is defective. Retract trailing edge flaps to FLAP UP position. Remove lower pan from flap control unit and install rigging pin  Replace leading edge flap and slat control valve. See Leading Edge Flap and Slat Control Valve -Removal/Installation, 27-81-81  Repair wiring as required  Replace standby shutoff valve. See Leading Edge Standby Valve -Removal/Installation, 27-81-91  Adjust leading edge flap and slat control valve 

500 
Feb 15/73  27-81-0 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

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27-81-0 Page 102  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Oct 20/92 

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Oct 20/85  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  27-81-0 Page 103 

LEADING EDGE FLAPS AND SLATS - MAINTENANCE PRACTICES
1. General
A.  Hydraulic systems A and B and the standby hydraulic system must be depressurized prior to performing maintenance on leading edge flap and slat control system components. This is to prevent injury to personnel, resulting from inadvertent operation of the control system while maintenance is being performed. Care must be exercised to locate maintenance stands and items of ground equipment beyond the limits of travel of leading edge flaps and slats and trailing edge flaps.
WARNING:  PRESSURIZING HYDRAULIC SYSTEMS FOR OPERATION OF THE LEADING EDGE FLAPS AND SLATS ALSO PERMITS OPERATION OF THE TRAILING EDGE FLAPS AND GROUND SPOILERS SIMPLY BY MOVING THE RESPECTIVE CONTROLS. OTHER FLIGHT CONTROL SYSTEMS MAY BE ISOLATED BY SHUTOFF VALVES. ISOLATE OR TAG ALL FLIGHT CONTROL SYSTEMS NOT BEING TESTED AND ENSURE THAT PERSONNEL AND EQUIPMENT ARE CLEAR OF CONTROL SURFACES BEFORE APPLYING HYDRAULIC POWER.
B.  Hydraulic system B electric pumps are used to pressurize hydraulic systems A and B for operation of leading edge flaps and slats. This is to avoid the necessity of operating the engines to power the hydraulic system A engine-driven pumps.
C.  When operating hydraulic system B pumps to pressurize hydraulic systems A and B, the following requirements must be observed:
(1)  
At least 1675 pounds (761 kilograms) of fuel is required in the No. 2 fuel tank to provide hydraulic fluid cooling. On hot days, or when fuel temperature is known to be above 90°F (32.2°C), monitor the system B overheat indicator and switch pumps off when overheat is indicated.

(2)  
Intermittent system B pump operation is limited to five starts of any one pump in a 5-minute period. Following the fifth start, run pump for at least 5 minutes or turn pump off for a minimum of 30 minutes.

D.  The following procedures (par. 3 and 4) cover depressurization and pressurization of hydraulic systems A and B through operation of electrically driven hydraulic system B pumps only. Par. 5 provides instructions for the application of leading edge flap and slat locks to prevent extension and retraction of the leading edge flaps and slats.
2.  Equipment and Materials
　
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