G08687 G08937
527 Tab Lock Actuator and Tab Travel Schematic
May 01/74 Figure 6 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 27-31-0 Page 13
Elevator Hydraulic System Schematic 525
27-31-0 Figure 7 May 01/75
Page 14
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
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 Fig. 5 and Chapter 22, Autoflight).
C. In the event of a failure of either hydraulic system A or B, the remaining system is capable of sustaining normal elevator control. A mechanical input from the control columns will be transmitted through the control system to both power control units. The control unit receiving hydraulic pressure will respond when the main control valve is displaced. The depressurized power control unit will be driven by the operating control unit through the output torque tube linkage.
D. In the event of failure of both hydraulic system A and hydraulic system B, a manual reversion mode will allow full elevator control by mechanical means. A noticeable deadband exists when the elevator system is controlled manually. During manual operation, an input to the control system moves the elevator PCU input crank until the crank contacts system stops. Then the PCU serves as a link to drive the elevator. In the manual reversion mode, elevator movement is assisted by tabs and aerodynamic balance panels. With loss of hydraulic pressure, the tab lock actuator is retracted by return springs. This action changes the geometry of the tab lock linkage to allow tab movement in a balance direction, which provides an aerodynamic force to assist elevator movement. As the elevator is displaced from neutral, a pressure differential is generated across the balance panels to reduce elevator control forces. The use of autopilot is not possible when the airplane is in manual reversion mode.
E. A modular assembly consisting of six hydraulic isolation valves is mounted to structure in the empennage, aft of the pressure bulkhead. An isolation valve is installed in each of the system A and B hydraulic lines to the feel computer, the elevator power unit and tab actuator, and the rudder power unit. The valves are manually operated and provide a means of isolating individual hydraulic components for ground leakage and flow tests.
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Feb 20/89 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 27-31-0 Page 15
ELEVATOR AND TAB CONTROL SYSTEM -TROUBLE SHOOTING
TROUBLE PROBABLE CAUSE ISOLATION PROCEDURE REMEDY
Insufficient Elevator control Check for proper rigging of Rig elevator control
elevator system out of rig. elevator control system. (Ref system as required.
travel. Foreign objects interfering with elevator system components. Forward quadrant stops incorrectly installed. Excessive system feel forces. 27-31-0, Adjustment/Test). Check for foreign objects in area of column, forward and aft quadrants, output torque tube and centering unit. To determine if problem is in centering unit, disconnect centering unit input rod and check elevator travel. With hydraulic power on, first check that column forces are not excessive. Check if quadrant is contacting stops before required travel is obtained. Refer to trouble shooting item: Excessive force required to move control columns, power on. Remove foreign objects or interference. Correct improper installation.
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