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MAINTENANCE MANUAL

SEE A  OUTPUT ARM QUADRANT CAPTAIN'S AFT  AFT QUADRANT FIRST OFFICER'S OUTPUT ARM 
CONTROL ROD 
ROD CONTROL  SEE  B  TUBES TORQUE QUADRANT AFT 
SEE  C 
FWD  A  FEEL UNIT  RIG PIN E/ST10 HOLE MECHANISM AND OVERRIDE NEUTRAL SHIFT 
FEEL UNIT ELEVATOR 
TORQUE BOX AFT MECHANISM 

FEEL ACTUATOR ELEVATOR  SPRINGS (4 PLACES) DECENTERING 
DIFFERENTIAL (3 PLACES) TRANSDUCER (RVDT) ROTARY VARIABLE  B  OUTBD  FWD 
Figure 5 (Sheet 1) Elevator Aft Mechanism Components 

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ASYMMETRY LIMITER ACTUATOR
CAPTAIN'SAFT QUADRANT
FIRST OFFICER'S AFT QUADRANT
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757
MAINTENANCE MANUAL

RIG PIN E/ST7 HOLE
FWD AFT MECHANISM TORQUE BOX
AUTOPILOT SERVO (3 PLACES)
ELEVATOR FEEL UNIT
C

Elevator Aft Mechanism Components
Figure 5 (Sheet 2)

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MAINTENANCE MANUAL

 E. Elevator Power Control Actuator (PCA) (Fig. 6)
 (1)  
Each elevator is positioned by three hydro-mechanical servo actuators. The PCA's are mounted on the horizontal stabilizer rear spar. The PCA's are each powered by a separate hydraulic system. Each PCA consists of a balanced piston, a slide/sleeve four-way servo valve, and mechanical summing linkage. Each PCA includes an overtravel mechanism downstream of the mechanical summing lever. This ensures that full control system inputs can be applied in either direction with the piston in the full opposite direction without transmitting excessive loads to the control linkage. The PCA's receive control inputs from the aft quadrants.

 F.
Elevator (Fig. 6)

 (1)  
Two elevator control surfaces are hinged on the rear spar of the stabilizer. Each elevator is driven by three power control actuators. The elevators are used primarily for maneuvering with pitch trim provided by the horizontal stabilizer.

 G.
Elevator Feel Computer (Fig. 6)

 (1)  
The feel computer is a dual hydro-mechanical unit that generates two independent feel pressures. The pressures are a function of airspeed impact pressure and horizontal stabilizer position. The computer consists of two separate units, one for each hydraulic system (right and center). Each unit is a force balance valve that develops regulated hydraulic feel pressure to balance the forces developed from the pressure differential (total pressure minus static pressure) across a diaphragm. The two feel pressures are monitored by two identical differential pressure sensing mechanisms. When one feel pressure differs significantly from the other feel pressure, an electrical switch generates a fault message to the pilot on the EICAS status page.

 H.
Elevator Feel Unit and Actuator (Fig. 5)

 (1)  
The elevator feel unit and actuator are installed on the aft mechanism torque box. The feel unit generates column force by two means: (a) dual mechanical centering springs, and (b) a hydraulic feel actuator. The feel actuator is a dual-tandem, dual-load-path, floating-body actuator. The force output of the actuator is the force determined by the highest of the two feel pressures. The actuator imparts a pull force on the linkage of each output lever through the dual load path link and tie straps. The tie straps are arranged to give a high force gradient around neutral and lower force gradient for large displacements.

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