27-11-00
 ALL  ú ú 02 Page 15 ú Nov 12/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 C.  Rotation of the control wheels rotates the control quadrant torque tube and applies an input to the power control unit input crank. As the input crank displaces the main control valve slide, hydraulic pressure is directed through the valve to move the main actuator piston. Movement of the input crank in the opposite direction displaces the main control valve slide to route hydraulic pressure to the other side of the main actuator piston. The actuator piston rod end is attached to structure, thereby causing the power control package body to extend or retract. Movement of the power control unit will return the input crank to neutral and close the main control valve. This will equalize the pressures on either side of the actuator piston and arrest further motion.
 D.  The upper power control unit and autopilot share the same input rod crank on the aileron control shaft assembly. For autopilot equipment, refer to Chapter 22, Autoflight.
 12. Operation
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 A.  The ailerons may be actuated either hydraulically or mechanically. For normal operation, hydraulic pressure from both systems A and B is utilized (Fig. 10). Motion is initiated by the aileron control wheels and aileron trim control switches (Fig. 2). Rotation of either aileron control wheel initiates motion in the aileron control cables which connect the control wheel drum to the aileron control quadrant. The cable motion is transferred from this quadrant through control linkage to the power control units. Motion of the main control valves in the power control units delivers hydraulic power to the actuator pistons which rotate cranks on the shaft connected to the bus drums. Rotation of the bus drums is 40 degrees in each direction from neutral, this is transferred through the bus system cables and aileron bus quadrants to rotate the ailerons 20 degrees in each direction from neutral position. Power control unit movement also provides spoiler system input through the aileron spring cartridge. Movement of the ailerons actuates the balance tabs. Hydraulic system A and B pressures to the aileron power control units are controlled by the flight controls shutoff valves in the flight controls hydraulic modular packages. A shutoff valve switch for each system is located on the overhead panel. Each hydraulic modular package is equipped with a low pressure warning switch which controls an amber light for each hydraulic system on the overhead panel. In the event of failure of either hydraulic system A or B, normal powered operation of the ailerons will be retained. In the event of failure of both hydraulic systems A and B, manual operation will take place. During manual operation, the aileron trim switches will not provide aileron trim.
 B.  Operation of the aileron trim control switches on the control stand alters the position of the centering spring mechanism. This provides an input to the aileron control linkage which changes aileron neutral and thus provides aileron trim. The available aileron trim provides 15 degrees aileron travel in both directions from neutral. The centering spring mechanism also provides artificial feel. The artificail feel force increases as the control wheel is rotated to obtain maximum aileron deflection.
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 27-11-00
 ALL  ú ú 01 Page 16 ú Nov 15/98
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
1 2 3  STDBY RUD OFF A ON  A B SPOILER A LOW PRESSURE LOW PRESSURE FLT CONTROL B  STANDBY HYD ALTERNATE FLAPS OFF B ON UP RUD STDBY OFF LOW PRESSURE LOW QUANTITY ARM DOWN OFF 
4  OFF ON YAW DAMPER YAW DAMPER  ON OFF  FAIL MACH TRIM FAIL FAIL FEEL DIFF SPEED TRIM PRESS AUTO SLAT 
ON OFF 
P5 PILOTS OVHD PANEL 
P  P 
R  R 
TO INBOARD SPOILERS  "A" SYSTEM PRESSURE 3  1  AILERON POWER UNIT "A"  AILERON POWER UNIT "B"  2  TO OUTBOARD SPOILERS "B" SYSTEM PRESSURE 4 
M  M  PS  PS  M  M 
AND ELEVATOR POWER UNITS TO RUDDER 
TO "A" SYSTEM RETURN  MODULAR UNIT  MODULAR UNIT  TO "B" SYSTEM RETURN 

Aileron Hydraulic System Schematic
Figure 10

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