22-11-00
ú ú 04 Page 15 ú Feb 25/87
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
D. A CMPTR flag in the ADI is controlled by DC valid voltage from the FCC.
7. Control Wheel Steering (CWS) Force Transducers______________________________________________
A. Three identical force transducers are installed in the captains and first officers control columns, two in the pitch axis and one in the roll axis. The pitch axis force transducers are located in the forward control quadrants below each control column. The roll axis force transducer is mounted between the control shaft and aileron drum below the captain's control column.
B. Each force transducer provides dual electrically isolated ac output signals that are proportional to the force applied to the control wheel or column. The signals are used by the autopilot computers when the system is engaged in CWS (manual) mode or in CMD mode with no flight mode selected. When the autopilot is engaged in a CMD mode the CWS signals are monitored. CWS signals, above a preset level (high detent), will cause the CMD mode to disconnect and the CWS mode to engage.
8. Aileron Force Limiter_____________________
A. The force limiter is splined to the aileron drum at the bottom of the captain's control column. The force limiter consists of an electromechanical clutch, switch, a spring-loaded arm and cam assembly, plus motor-driven limit switches. The electromechanical clutch and switch are activated when the roll axis is engaged. The force limiter mechanically limits the control wheel angle by progressively increasing the force within the system to cam out autopilot control at the A/P actuator. Motor-driven switches within the force limiter, which are controlled by trailing edge flap position, determine the control wheel angle limit. With trailing edge flaps up, the limit is 17 degrees. With trailing edge flaps down (1 unit position and beyond) the limit is 25 degrees. This limits the rate of roll which the autopilot can command, and thereby, limiting autopilot hardover maneuver capability. The clutch switch ensures the force limiter is engaged. If the clutch disengages, the switch opens the A/P engage switch holding coil circuit.
B. The captain or first officer may override the force limiter by applying sufficient force on the control wheel to drive through the limiting mechanism. The autopilot continues to drive the A/P actuator throughout the control wheel steering regime after the control wheel is returned to less than 25 or 17 degrees.
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22-11-00
ú ú 03 Page 16 ú Nov 12/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
C. The force limiter is deactivated when the autopilot is disengaged, regardless of control wheel position.
9. Autopilot Actuators (Fig. 3)___________________
A. Four autopilot actuators are installed, two in the main wheel well area for the aileron axis and two in the aft fuselage for the elevator axis. One set, aileron and elevator, is controlled by the A autopilot system and the other set by the B autopilot system. The units are mechanically linked to aileron and elevator power control units (PCU's) which drive the flight control surfaces.
B. A pressure switch is installed on each actuator. The switch closes when normal hydraulic pressure is applied to the PCU. The engage interlock voltage is wired through the switches to ensure proper hydraulic pressure for autopilot operation.
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