COLUMN AGAINST STOP
STABILIZER CHORD PLANE
ELEVATOR RIGGED POSITION
COLUMN AGAINST STOP
SHOWN WITH STABILIZER AT ZERO DEGREES.
ANGULAR DIMINSIONS ARE APPROXIMATE.
Tab Control Actuator and Tab Travel Schematic
Figure 6

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A
737-300/400/500MAINTENANCE MANUAL
 12. Operation (Fig. 7)_________
 A.  The elevators may be operated manually by means of mechanical linkage or hydraulically using system A and system B hydraulic pressure. Forward or aft movement of the control columns transmits motion through two sets of control cables to the aft control quadrants. Motion is then transmitted through a pair of input rods and cranks to the power control units. This mechanical linkage from the control columns is utilized during either manual or hydraulic operation. During manual operation, the power control unit input cranks contact stops and use the power control units to mechanically drive the linkage to the elevators. Elevator neutral position relative to stabilizer is determined by stabilizer attitude. The range of elevator neutral shift varies with mach trim actuator position. With the stabilizer at 3 units of trim, the elevator neutral position is 4 degrees down from faired. As the stabilizer leading edge moves down the elevator neutral position moves up. When the stabilizer moves to 10 units of trim, the elevator neutral is at zero degrees, and with the stabilizer at 14 units of trim, the elevator neutral is 2-3/4 degrees up. Elevator maximum travel with the stabilizer at zero units is 20 degrees up and 22 degrees down.
 B.  Hydraulic system A and B pressures to the power control units and feel computer, are regulated by the flight controls hydraulic modular units located in the main wheel well. The modular units are electrically-operated by two switches on the overhead panel, one switch serves system A, the other switch, system B. Pilots' input causes a rotation of the input crank, which in turn moves the main control valve. Operation of the main control valve allows fluid to pressurize one side of the main actuator piston, causing the power control unit to extend or retract, thereby rotating the elevators up or down. Movement of the control unit in either direction returns the input crank to neutral which closes the main control valve. Elevator feel forces are provided by the dual feel actuator and a spring-loaded centering cam in the elevator feel and centering unit. Feel forces developed are directly proportional to elevator displacement from neutral. Engaging the autopilot will allow autopilot position signals to activate the elevator control system (Ref Chapter 22, Autoflight).
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A 737-300/400/500MAINTENANCE MANUAL
FLT CONTROL STANDBY
A B HYD
LOW
QUANTITY

STDBY STDBY RUD RUD LOW PRESSURE
OFF OFF
A ON B ON
ALTERNATE FLAPS
OFF

UP
PRESSURE

LOW LOW
PRESSURE
OFF
SPOILER
AB

DOWNARM
ELEVATOR DUAL
OFF OFF
FEEL ACTUATOR
FEEL DIFF
PRESS
ON ON

SPEED TRIM
FAIL

MACH TRIM
YAW DAMPER FAIL

YAW AUTO SLAT
DAMPER FAIL

OFF
DIFFERENTIAL
ON
PRESSURE SWITCH
PILOTS' OVERHEAD PANEL
FEEL COMPUTER 
TO RUDDER POWER UNIT  TO RUDDER POWER UNIT 
P  P 
R  R 
TO INBOARD SPOILERS "A" SYSTEM PRESSURE  ELEVATOR POWER CONTROL UNITS  TO OUTBOARD SPOILERS "B" SYSTEM PRESSURE 
M  M  PS  TO AILERON POWER UNIT "A"  TO AILERON POWER UNIT "B"  PS  M  M 
HYDRAULIC ISOLATION VALVES 
TO "A" SYSTEM RETURN  FROM AILERON POWER UNIT "A"  FROM AILERON POWER UNIT "B"  TO "B" SYSTEM RETURN 

Elevator Hydraulic System Schematic
Figure 7

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