BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

 (5)  
AIRPLANES WITH STAB TRIM LEVERS ON THE CONTROL STAND; the horizontal stabilizer is hydraulically powered and manually or electrically controlled. The stabilizer recieves power from the right and center hydraulic systems.

 (6)  
AIRPLANES WITH ALTERNATE STAB TRIM SWITCHES ON THE CONTROL STAND; the horizontal stabilizer is hydraulically powered and electrically controlled. The stabilizer recieves power from the right and center hydraulic systems.

 C.
Flight Control Actuators, Servos, and Electronics

 (1)  
Three autopilot lateral control servos (ALCS) provide automatic control . Each ALCS is powered by a separate hydraulic system. The ALCS's have internal servovalves for autopilot inputs. All of the ALCS's have the same part number.

 (2)  
A total of twenty-five power control actuators move the control surfaces. Each PCA uses one of the three hydraulic systems.

 (3)  
Six autopilot servos provide electronic control inputs to the flight control systems. There are three elevator servos and three directional servos. The elevator and directional servos use all three hydraulic systems. Each hydraulic system supplies one elevator servo and one directional servo. The two pitch augmentation servos are also supplied by separate hydraulic systems.

 (4)  
Two yaw damper servos provide gust damping inputs to the rudder system. Each servo uses one of two hydraulic systems. The two yaw damper servos have the same part number.

 (5)  
The control system electronics unit (CSEU) is a group of power supply and electronic modules used in the flight control system. There are two (left and right) CSEU's installed for redundancy.

 D.
Flight Controls - Hydraulic Distribution

 (1)  
Three independent hydraulic systems provide power to the flight controls. Each system uses a combination of pumps to supply power.

 (2)  
Flight control redundancy is provided by the use of multiple hydraulic systems. The aileron, elevator, rudder, and spoiler PCA's use all three hydraulic systems. The elevator and directional servos and ALCS's each use one of the three hydraulic systems. The slats, flaps, and rudder ratio changer use a single hydraulic system.

 (3)  
The ram air turbine (RAT) is an emergency hydraulic source. The RAT is used in the event of a double engine failure. The RAT is used by the primary flight control system only.

 (4)  
The tail shutoff valves are used for system isolation. The valves are provided for ground use only. The valves are normally open in flight.

 (5)  
Safety harness attachment receptacles are provided on the wing and horizontal stabilizer upper surfaces for use by maintenance personnel working high above ground (Ref 20-10-27, Flight Controls Safety Harness Receptacle).

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757 MAINTENANCE MANUAL
 FLIGHT CONTROL CABLES - DESCRIPTION AND OPERATION
_________________________________________________
 1.  General_______
 A.  The flight control cables transmit pilot control inputs to the related control surfaces. A typical control cable ends at a drum or quadrant using swaged terminals. The cables are tensioned to the proper rigging load by turnbuckles. Long cable runs are supported by idler pulleys. Air pressure seals are used to reduce pressure loss when cables are routed through pressure bulkheads and decks.
 B.  Control cable runs are identified by code letters which identify cable function (AMM 27-00-01/201).
 2.  Component Details_________________
 A.  Ailerons
 (1)  
Aileron control cables are routed from the left and right control column quadrants, under the flight deck and main cabin compartment floors. The cables pass through sloping pressure deck air pressure seals and are deflected by pulleys into the main gear wheel wells. The cables on the left side stop at the lateral control feel, centering and trim mechanism. The cables on the right side stop at the quadrant for the lateral control override mechanism. Cables from the feel, centering and trim mechanism operate the left side aileron power control actuators (PCAs). Cables from the override mechanism control the right side PCAs.
　
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