(b)
P180, DC Power Distribution Panel
1) 180H08, ELEV/RUD VLV SYS 1
2) 180E07, ELEV/RUD VLV SYS 2
3) 180H23, ELEV/RUD VLV SYS 3
4) 180E22, ELEV/RUD VLV SYS 4
S 862-084
(2)
Set the STAB TRIM 2 and 3 switches on the Pilots' Control Stand to the ON position.
S 862-085
(3)
Set the FLT CONTROL HYD POWER TAIL 1, 2, 3, and 4 switches to the NORM position. These switches are on the Pilots' Overhead Maintenance Panel (P461).
S 712-075
(4)
Do this task: "Operational Test - Yaw Damper System"
(AMM 22-21-00/501).
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747-400 MAINTENANCE MANUAL
S 862-086
(5)
Set the STAB TRIM 2 and 3 switches on the Pilots' Control Stand to the OFF position.
S 862-087
(6)
Set the FLT CONTROL HYD POWER TAIL 1, 2, 3, and 4 switches to the SHUTOFF position. These switches are on the Pilots' Overhead Maintenance Panel (P461).
S 862-078
(7)
Open these circiut breakers and attach the DO-NOT-CLOSE tags:
(a) P180, DC Power Distribution Panel
1) 180H08, ELEV/RUD VLV SYS 1
2) 180E07, ELEV/RUD VLV SYS 2
3) 180H23, ELEV/RUD VLV SYS 3
4) 180E22, ELEV/RUD VLV SYS 4
S 792-079
(8) Visually examine the valve to make sure that there is no hydraulic leak.
D. Airplane Back to Its Initial Condition
S 862-080
(1)
Close these circuit breakers and remove the DO-NOT-CLOSE tags:
(a) P180, DC Power Distribution Panel
1) 180H08, ELEV/RUD VLV SYS 1
2) 180E07, ELEV/RUD VLV SYS 2
3) 180H23, ELEV/RUD VLV SYS 3
4) 180E22, ELEV/RUD VLV SYS 4
(2)
Install the applicable access panel(s)(AMM 06-09-07/201).
S 412-083
NOTE: The 324UL/324UR access panel is for the upper RPCM.
____ The 324DL/324DR access panel is for the lower RPCM.
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747-400 MAINTENANCE MANUAL
AUTOMATIC STABILIZER TRIM SYSTEM - DESCRIPTION AND OPERATION
____________________________________________________________
1. General_______
A. The Automatic Stabilizer Trim (AST) System provides automatic trim control of the horizontal stabilizer position to reduce the load on the elevator. This section covers all automatic stabilizer trim component locations, the component functions, the interfaces, and the purpose of each component. The different modes of operation are also provided along with a description of the system failure monitors and the displayed fault messages.
B. This sections emphasis is on automatic stabilizer trim, but most components are an integral part of the manual electric stabilizer trim system. For complete stabilizer system description, refer to Horizontal Stabilizer Trim Control System (AMM 27-41-00/001). The stabilizer trim system is designed to provide two trim paths (left channel and right channel) that are capable of independent operation. Half rate trim is single channel operation and full rate trim is dual channel operation. The output from the channels is mechanically summed at the gearbox, dual channel trim results in twice the trim rate of single channel trim. Each channel is further broken down into separate signal paths - ARM and CONTROL, which must agree throughout the signal path in order to produce a trim command to the stabilizer.
C. Figure 1 shows most of the flight deck components involved in the automatic stabilizer trim (AST) system. These include captain's and first officer's manual electric trim switches on the outboard horn of each control wheel; alternate electric trim switches, stab trim hydraulic cutoff switches, and stabilizer position indicators on pilots' control stand; and elevator actuated stabilizer trim cutout switches under the cabin floor in the elevator forward quadrant.
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