STABILIZER
Stabilizer Trim Control System
Figure 1
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27-41-00
ALL ú ú 01 Page 1 ú Feb 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
D19384
A
747-400
MAINTENANCE MANUAL
D. Hydraulic power for the stabilizer trim system is obtained from No. 2 and 3 airplane hydraulic systems. Each system supplies power to an independently functioning group of components. Each group of components consists of a STCM, a hydraulic motor and a hydraulic brake. No. 2 hydraulic system supplies the right component group (A system); No. 3 hydraulic system supplies the left component group (B system). Two normally ON, guarded switches on the control stand control hydraulic power to the stabilizer system. These switches, designated STAB TRIM 2 and 3, control motor-driven valves on the STCMs.
E. Stabilizer trim cutout switches are located on the right hand side of the center aisle stand. The switches are a three position toggle switch. The CUTOUT position closes the motor-operated-shutoff valves in the STCMs, removing hydraulic power from the stabilizer trim drive mechanism. The ON position open the motor-operated-shutoff valves in the STCMs, enabling trim control through the STCM. The AUTO position renders control of the motor-operated-shutoff valves to the SRM. Override capability is provided to the ON and CUTOUT positions over the automatic control.
F. Travel limiting devices control the range of stabilizer movement in all operating modes. In the electrical control modes, limit switches internal to the SRM prevent stabilizer travel beyond that required by the normal flight envelope for the prevailing operating condition (manual-electric, autopilot). Mechanical stops on the actuator constrain absolute travel, but the trim system does not normally drive the stabilizer to these stops.
G. Two horizontal stabilizer trim indicators, mounted one on each side of the control stand in the control cabin, provide visual indication of stabilizer position.
H. Three stabilizer position transmitters are located at the aft end of the stabilizer center section. Each contains a synchro transmitter and an RVDT transmitter. The left and right position transmitters provide synchro inputs to the stabilizer position indicators on the control stand. Input from the RVDT mechanical position transmittier is sent to the flap control unit (FCU) where it is processed and routed to the EIU's for display on the EICAS flight control maintenance page. The synchro in the center position transmitter is not used. Refer to 27-48-00/001 for detail of position transmitter operation.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
CONTROL WHEEL P7 PANEL CONTROL STAND
SEE A SEE C STABILIZER
TRIM MANUAL
P6 PANEL CONTROL
SWITCHES
CONTROL WHEEL
ELEVATOR
A
CONTROL ACTUATED CUTOUT E1-2
SWITCHES SEE D
MAIN EQUIP CTR
L, R, STABILIZER
SEE B TRIM/RUDDER RATIO MODULES
117AR
CAPT, F/O
ACCESS DOOR
HORIZONTAL STABILIZER POSITION STABILIZER
INDICATORS
TRIM SHUTOFF
VALVE SWITCHES
MAIN EQUIP CTR
ALTERNATE
B
ELECTRIC MANUAL AND AUTOPILOT
STABILIZER A DOWN LIMIT SWITCH
TRIM SWITCHES AUTOPILOT B DOWN LIMIT SWITCH
CONTROL STAND MANUAL AND AUTOPILOT UP SWITCH
AUTOPILOT B UP LIMIT SWITCH
FWD
CONTROL STAND
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