27-41-00
CONTROL STAND ú ú 02 Page 2 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
LIMIT SWITCH AND
STABILIZER
POSITION TRANSMITTER
POSITION
MODULE (EXAMPLE)
MODULE (EXAMPLE)
Stabilizer Trim Control System
Figure 1 (Sheet 2)
A
757
MAINTENANCE MANUAL
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH ALTERNATE STAB TRIM ú
27-41-00
SWITCHES ON THE CONTROL STAND ú ú 02 Page 3 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
H. AIRPLANES WITH STAB TRIM LEVERS ON THE CONTROL STAND; travel limiting devices control the range of stabilizer movement in all operating modes. In the electrical control modes, limit switches within the stabilizer trim limit switch and position transmitter modules (LSTMs) prevent stablilizer travel beyond that required by the normal flight envelope (Ref 27-48-00). In the mechanical control mode, a cable system repositions valves in the STCMs to shutoff power to the drive hycraulic motors before stops are reached.
I. AIRPLANES WITH ALTERNATE STAB TRIM SWITCHES ON THE CONTROL STAND; travel limiting devices control the range of stabilizer movement in all operating modes. In the electrical control modes, limit switches within the stabilizer trim limit switch and position transmitter modules (LSTMs) prevent stabilizer travel beyond that required by the normal flight envelope (Ref 27-48-00).
J. Stabilizer position data is generated by three stabilizer trim limit switch and position transmitter modules (LSTM's). The modules are driven by mechanical cables attached to the stabilizer. The modules transmit position data to the SAM's, the FCC's, and a pair of position indicators on the flight deck (Ref 27-48-00).
K. AIRPLANES WITH STAB TRIM LEVERS ON THE CONTROL STAND; system redundancy and protective devices prevent stabilizer uncommanded motion. Each of the trim channels is dualized, requiring separate electrical and hydraulic ARM and CONTROL signals to port fluid to the hydraulic motors. All electrical trim commands can be overridden by use of the manual trim cable system. Hydraulic power to each control module can be removed by a shutoff switch located on the quadrant stand. The switch controls a motor-operated shutoff valve in the STCM. Cutoff switches operated by control column motion in opposition to stabilizer motion will interrupt electrical trim commands. Failure detection/annunciation is provided for stabilizer trim motion without a valid trim command and for failures resulting in half rate trim operation.
L. AIRPLANES WITH ALTERNATE STAB TRIM SWITCHES ON THE CONTROL STAND; system redundancy and protective devices prevent stabilizer uncommanded motion. Each of the trim channels requires separate electrical ARM and CONTROL signals to send hydraulic fluid to the motors. Hydraulic power to each control module can be removed by a shutoff switch that is on the control stand panel. The switch controls a motor-operated shutoff valve in the STCM. Cutoff switches operated by the control column motion in opposition to stabilizer motion will interrupt primary electrical trim commands. Failure detection/annunciation is provided for stabilizer trim motion without a valid trim command and for failures resulting in half rate trim operation.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
27-41-00
ALL ú ú 01 Page 4 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
2. Component Details
_________________
A. Stabilizer Trim Control Wheel Switches (Fig. 2)
(1)
Two sets of dual switches, located in the captain's and first officer's control wheels, actuate the stabilizer trim system in the manual-electric control mode. The two switches in each set are mounted side-by-side on the control wheel such that both can be actuated simultaneously with one thumb. Each switch set consists of two single pole, three position, center off switches. The stabilizer trim control wheel switches enable the captain or first officer to input manual trim commands to both SAM's. Actuating both switches in airplane nose up direction inputs simultaneous airplane nose up (stab LE down) arm and control commands. Airplane nose down actuation inputs airplane nose down (stab LE up) arm and control commands.
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