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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Flaps do not retract automatically from 40-to 30-units when airspeed exceeds 152 to 162 knots Flaps do not retract automatically *[1] Flaps position indicator points left and right are split and at the same time the primary flap drive system continues to update  Faulty flap load limiter solenoid valve (V94)Faulty flap position Faulty flap asymmetry shutoff relay (R123)  Position flap handle to 40-units. Hold flap load limiter test switch in SYSTEM TEST. Check that flaps retract. Release switch and check that flaps extend Perform flap asymmetry shutoff system test (Ref. 27-51-001501)  Perform test 27-51-321 to determine which airspeed switch is defective. Replace defective switch  Replace valve Replace flap position indicator (Ref. 27-58-41/401) Replace flap asymmetry shutoff relay, R123 

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27-51-0  Aug 01/96 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

TRAILING EDGE FLAPS - MAINTENANCE PRACTICES
1. General
A.  System A hydraulic system must be depressurized prior to performing maintenance on trailing edge flaps. 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 trailing edge flaps and leading edge flaps and slats.
WARNING:  PRESSURIZING HYDRAULIC SYSTEMS TO OPERATE THE TRAILING EDGE FLAPS ALSO ACTIVATES THE LEADING EDGE FLAPS AND SLATS, RUDDER, ELEVATOR, AND AILERON HYDRAULIC SYSTEMS. ISOLATE OR TAG ANY SYSTEM NOT BEING TESTED AND ENSURE THAT PERSONNEL AND EQUIPMENT ARE CLEAR OF CONTROL SURFACES BEFORE APPLYING HYDRAULIC POWER.
OPERATING THE TRAILING EDGE FLAPS WILL AUTOMATICALLY OPERATE THE LEADING EDGE FLAPS.
B.  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.

C.  The following procedure covers pressurization of hydraulic system A through operation of electric driven hydraulic system B pumps only. Pressurization of hydraulic system A through operation of engine driven hydraulic system A pumps is not covered.
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Feb 15/73  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  27-51-0 Page 201 

2.  Trailing Edge Flaps Hydraulic System A Pressurization
A.  Equipment and Materials
(1)  Ground Lock Assembly - F72735
B.  Pressurize Trailing Edge Flaps Hydraulic System A 
(1)  
Install ground lock assembly in nose gear.

(2)  
Provide electrical power.

(3) 
 Set parking brake.

(4)  
Position GRD INTERCONNECT switch on forward overhead panel to OPEN.

(5)  
Close FLAP circuit breaker on P6 circuit breaker panel.

(6)  
Position No. 1 or 2 system B HYD PUMPS switches on forward overhead panel to ON, to pressurize hydraulic systems A and B.

C.  Restore Airplane to Normal
NOTE:  Perform following steps after completing system maintenance that required pressurization.
(1)  
Position No. 1 and 2 system B HYD PUMPS switches to OFF.

(2)  
Position GRD INTERCONNECT switch to CLOSE.

(3)  
Remove electrical power if no longer required.

(4)  
Remove ground lock assembly from nose gear.

3.  Trailing Edge Flaps Hydraulic System A Depressurization
A.  Equipment and Materials
(1) Lock Assembly - Flight Controls F80049-12 (Preferred) or F80049-2 (Optional)
B.  Depressurize Trailing Edge Flaps Hydraulic System A
(1)  
Open FLAP circuit breaker on P6 circuit breaker panel.

(2)  
Position ALTERNATE FLAPS switch on forward overhead panel to OFF.

(3)  
Position No. 1 and 2 system B HYD PUMPS switches on forward overhead panel to OFF.

(4)  
Position GRD INTERCONNECT switch on forward overhead panel to CLOSE.
　
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