Flap Drive System (Fig. 5).

 (a)  
The flaps are positioned by two ballscrew actuators attached to each flap. The ballscrews are driven through a system of transmissions and gearboxes which attach to the torque tube system. The torque tubes extend out into each wing and are powered by the flap power drive unit (PDU).

 (b)  
Each flap rides on two flap tracks which determine the angle that the flap makes with the wing and which transfer the lifting forces of the flaps to the wing structure.

 (c)  
The aft flaps ride on tracks within the flap structure and are driven to the extended position by bellcranks and connecting rods.

 (d)  
The outboard flap track for the inboard flap is attached to the forward support fitting of the wing by a fuse pin. Both the inboard and outboard flap tracks for the outboard flap are attached to the wing by fuse bolts. These fuse pins and bolts shear under extreme load to prevent major damage to the wing structure.

Flap Load Relief (Fig. 6)
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MAINTENANCE MANUAL

SUPPORT 
MAIN FLAP  TRACKS 
A 
A 
SEE  A 
A 
MAIN FLAP 
AFT FLAP 
FLAP TRACK 
FLAP  FUSE 
SARRIAGE  PIN 
INBOARD FLAP 
SEE  B 
A-A 
TORQUE TUBE
TORQUE TUBE 
GEARBOX  BALLSCREW 
(TYP)  ACTUATOR (TYP) 
FLAP CARRIAGE 
FLAP TRANSMISSION 
(TYP 8 PLACES) 
B 
Flap Drive System 
Figure 5 (Sheet 1) 

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MAINTENANCE MANUAL

LEFT WING
PLAN VIEW

MAIN
FLAP

OUTBOARD FLAP
B-B

Flap Drive system
Figure 5 (Sheet 2)

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MAINTENANCE MANUAL

FSEU-1
Flap Load Relief System SchematicFigure 6
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757
MAINTENANCE MANUAL

 (a)  
The flap load relief system provides automatic retraction of the flaps from the 30-unit position to the 25-unit position to protect the flaps from excessive airloads.

 (b)  
The flap load relief system operates only when the flap lever is positioned in the 30-unit detent. FSEU-1 recieves airspeed data from the digital air data computer. If this speed exceeds 170 knots the FSEU sends a signal to the flap load relief solenoid on the flap control valve. The solenoid moves the control valve sleeve allowing hydraulic fluid to pass to the hydraulic motor and drive the flaps to the 25-unit position.

 (c)  
The flaps will return to the 30-unit position when airspeed is reduced to 165 knots.

 (d)  
The flap control lever will not change position during load relief.

 (e)  
The flap load relief system is inoperative when the alternate

 drive system is armed.Depressurization (Fig. 7)

 (a)  
The flap/slat depressurization module shuts off hydraulic power to the flaps and slats when the flaps have been retracted for 25 seconds or when the alternate drive systems are armed. Asymmetry or uncommanded motion causes hydraulic shutdown of the flap/slat systems as described in 27-58-00, Trailing Edge Flap System Position Indicating System - Description and Operation.
　
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