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HORIZONTAL STABILIZER CONTROL -POSITION MODULES

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Purpose

The horizontal stabilizer supplies long-term pitch control of the airplane.
Physical Description

The stabilizer is a light-weight composite material structure. The main torque boxes are carbon fiber construction with aluminum trailing edge hinge ribs. Steel hinge plates with fiberglass honeycomb panel fairings attach to the trailing edge of these ribs.
Forward of the main torque boxes are auxiliary boxes formed by aluminum sheet metal ribs that have covers made of fiberglass honeycomb panels.
The leading edges and the tips of the stabilizer are aluminum skinned honeycomb panels.
The horizontal stabilizer assembly weights approximately 6100 lbs (2765 kg). This includes the weight of the elevators and the PCUs. The horizontal stabilizer assembly measures about 71 feet wide by 34 feet long (21.6 meters by 10.4 meters).
There are four hoist points on the upper and lower surfaces on each side of the horizontal stabilizer assembly.
Functional Description
The stabilizer moves 15 degrees:
*
4 degrees leading edge up (4 degrees airplane nose down trim) from neutral

*
11 degrees leading edge down (minus 11 degrees airplane nose up) from neutral.

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777 AIRCRAFT MAINTENANCE MANUAL

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HORIZONTAL STABILIZER CONTROL -FUNCTIONAL DESCRIPTION -INTRODUCTION

General

The stabilizer control system uses input command signals from the captain’s and first officer’s pitch trim switches.
The ACEs receive the input signals and supply output command signals to the STCMs. The ACEs also receive feedback signals from the SPMs.
The stabilizer cutout switches and the auto shutdown relays send signals to the STCMs to close the motor operated shutoff valves.
The system also operates with mechanical commands from the alternate pitch trim levers directly to the STCMs.
Pitch Trim Switches

Each ACE receives a signal from a pitch trim switch. The L1 ACE receives the arm signal from the captain’s arm switch and the L2 ACE from the first officer’s arm switch. The C ACE receives the control signal from the captain’s control switch and the R ACE from the first officer’s control switch.
Stabilizer Cutout Switches and Auto Shutdown Relays

The stabilizer cutout switches directly control power to close the motor operated shutoff valve on the STCMs.
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Two ACEs control the auto shutdown relays individually. When commanded, each relay sends power to close a motor operated shutoff valve on an STCM.
Stabilizer Trim Control Modules
The center STCM requires the operation of the C and L1 ACEs.
The C ACE sends command signals through the auto shutdown relay to close the shutoff valve of the center STCM. The shutoff valve also receives command signals directly from the center stabilizer cutout switch. The center STCM also receives from the C ACE the control up or down command signals. These signals initially go through the limit switches of the center SPM before they command the control solenoids.
The center STCM receives arm up or down command signals and the rate solenoid signals from the L1 ACE.
The right STCM requires the operation of the R and L2 ACEs.
The R ACE sends command signals through the auto shutdown relay to close the shutoff valve of the right STCM. The shutoff valve also receives command signals directly from the right stabilizer cutout switch. The right STCM also receives the control up and down command signals from the R ACE. These signals initially go through the limit switches of the right SPM before they command the control solenoids.
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HORIZONTAL STABILIZER CONTROL -FUNCTIONAL DESCRIPTION -INTRODUCTION

The right STCM receives arm up or down command signals and the rate solenoid signals from the L2 ACE.
The brake pressure switch of the center STCM sends a feedback signal to the C ACE, the switch from the right STCM to the R ACE.
　
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