(2)  
Increased wing camber and area decreases stall speeds and allows the aircraft to be maneuvered at lower airspeeds. Lower aircraft stall speeds allow lower takeoff and landing speeds. This reduces ground roll, increases wheel and brake life, increases climb-out performance, and creates safer operating conditions.

 (3)  
There are two flaps on each wing, an inboard flap and an outboard flap. Each flap consists of a main flap and an aft flap. The flaps are faired with the wing for cruise conditions and are extended aft and downward at takeoff and landing.

 (4)  
During normal operation, the flaps are powered by the left hydraulic system. Normal flap operation is controlled by the flap control lever mounted on the pilot's control stand.

 (5)  
During alternate operation the flaps are electrically powered. Control of the flaps is provided by a guarded alternate drive arming switch and a rotary alternate flaps/slats position selector switch located on the center panel.

 (6)  
A flap position indicating system is provided to show flap position during extension and retraction. A combined flaps and slats dial indicator is located on the center instrument panel.

 B.
General Description

 (1)  
Trailing Edge Flap Primary Control (Fig. 3)

 (a)  
The flaps are normally controlled with the flap control lever on the center aisle stand. Movement of the flap control lever rotates a cable drum attached to the flap control cables. The flap control cables are connected to the input drum on the flap power drive unit (PDU) and cause rotation of the input drum.

 (b)  
The input drum is connected to a cam which rotates with the drum. This cam is linked to the control valve and positions the control valve spool. The control valve will pass hydraulic fluid to the retract or extend port of the PDU hydraulic motor depending upon flap control lever input.

 (c)  
As the flaps move towards the commanded setting a feedback mechanism repositions the control valve spool to a neutral position, stopping the hydraulic motor.

 (2)  
Trailing Edge Flap Alternate Control (Fig. 4)

 (a)  
Back up operation of the flap system is done electrically.

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A

757
MAINTENANCE MANUAL

AFT FLAP INBOARD FLAP AFT FLAP OUTBOARD FLAP
TORQUE TUBES SLAT PDU
FLAP CONTROL
MAIN FLAP CABLES
AFT FLAP
FLAP PDU

Trailing Edge Flaps
Figure 1

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A
757
MAINTENANCE MANUAL

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A
757
MAINTENANCE MANUAL

UP(RETRACTED)
152025 A
BC
D
E
F
G
H RIGHT POSITIONTRANSMITTER
JK
L

PRESSURE
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High Lift System Block Diagram
Figure 2 (Sheet 2)

A
757
MAINTENANCE MANUAL

SPRING LOADED
HANDLE TO L.E. SLATS PDUFWD
CABLE ATTACH
POINT

CONTROL VALVEINPUT CRANK
CONTT.E.T.E.FLAP HYD MOTORVALVE
FOLLOWUP CAM FLAP LEVER EXTENDPOSITION SENSOR
　
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