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27-41-00
ALL ú ú 01 Page 3 ú Jun 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
LEFT, RIGHT,
AND CENTER
POSITION
TRANSMITTERS
HORIZONTAL STABILIZER
HORIZONTAL STABILIZER JACKSCREW
HORIZONTAL STABILIZER
STABILIZER HYDRAULIC TRIM
BRAKES LIMITSTABILIZER SWITCHES
JACKSCREW
SEE E
LEFT AND RIGHT
STABILIZER
TRIM CONTROL
TRIM DRIVE MODULES
MECHANISM SEE F
HYDRAULIC MOTORS
AFT
RATE CONTROL
SOLENOID
STABILIZER JACKSCREW
E
ARM AND CONTROL
PRESSURE SWITCH
AFT
STABILIZER TRIM CONTROL MODULE (LEFT AND RIGHT)
F
Stabilizer Trim Control System Component Location Figure 2 (Sheet 2)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
27-41-00
ALL ú ú 12 Page 4 ú Oct 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
2. Stabilizer
__________
A. The horizontal stabilizer assembly comprises left and right outboard sections, attached to a center section by close tolerance lockbolts, and the left and right elevators. Details of the elevators are contained in 27-31-00. The three-piece leading edge and the tip fairing of each outboard section can be replaced with the stabilizer installed on the airplane.
B. The center box section and part of the horizontal stabilizer is used as an integral fuel tank, sealed to provide a fuel-tight compartment. Care must be taken when working around the stabilizer center box to avoid damage to the fiberglass spray shields and the fuel system components mounted behind them. Care must also be taken to avoid damage to the tank drain hoses that extend from the bottom of the center box to a fitting on the fuselage lower skin. For information on the fuel tank sealing and system components, refer to Chapter 28, Fuel.
C. Hard points in the upper surface of each outboard section provide sling attachments for hoisting the stabilizer assembly. Each attachment consists of four threaded holes sealed by countersunk screws. Body seal installations on each side of the stabilizer enclose the apertures in the empennage through which the stabilizer passes. Drain holes in the stabilizer lower skin prevent pockets of moisture from building up within the structure. A scupper on each side within the empennage collects water from the stabilizer center section. Hoses attached to the scuppers conduct the water to an overboard drain.
D. Attachment fittings for the stabilizer are mounted at the center section front and rear spars. The actuator fitting on the front spar accepts the upper gimbal of the stabilizer trim drive mechanism. Two hinge fittings aft of the rear spar pick up mating hinge fittings on the stabilizer hinge bulkhead. The stabilizer hinge bearings can be replaced with the stabilizer installed.
E. Safety harness attachments are provided on the stabilizer upper surface for use by maintenance personnel working high above the ground. Each stabilizer outboard section mounts two receivers which accept NORCO INC. lock assemblies type IL280-2. One receiver is located inboard forward of the front spar; the other, close to the inboard elevator PCP. Safety harnesses equipped with safety hooks, Rose Manufacturing Co., Part No. 2535 or equivalent, may be used.
3. Stabilizer Trim Switches
________________________
A. 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 segments in each switch are mechanically and electrically isolated from each other. Each segment operates a pair of solenoids on each STCM. One segment controls a pair of arming solenoids and the other, a pair of directional control solenoids. As an arming solenoid and its associated directional control solenoid must both be energized to trim the stabilizer, both segments must be held in the same direction to obtain movement. Hence, a malfunction in a single segment of circuit cannot cause runaway stabilizer.
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