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 ALL  ú ú 20 Page 9 ú Feb 18/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 8.  Trim Drive Mechanism Hydraulic Brakes
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 A.  The hydraulic brakes are also identical units and are configured identically for installation. Like the motors, they are easily accessible for changing with the trim drive mechanism installed. Each brake is of the pressure disk type, spring loaded to on. The brakes are mounted side by side on top of the bull gear housing. Friction lined stator disks are keyed to a rotating shaft which the associated hydraulic motor drives through a quill shaft. With the brake unit unpressurized, coil springs compress the stator and rotor disks firmly together, locking the shaft connected to the hydraulic motor. To release the brake, hydraulic pressure acts on a piston and compresses the coil springs. Separator springs then force the rotor disks away from the stator disks, freeing the shaft to rotate.
 9.  Stabilizer Trim Limit Switches
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 A.  Four rotary limit switches are mounted outboard on the aft face of the actuator bulkhead; two on the left side and two on the right. Cams attached to the stabilizer front spar actuate the switches. One pair of switches, on each side of the stabilizer, limit the stabilizer travel in the nose up and nose down directions for alternate electric trim operation (all other trim limiting is incorporated in the SRM for manual-electric, autopilot and speed trim operation).
 10. Elevator Control Actuated Limit Switches
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 A.  Four microswitches actuated by movement of the elevator forward quadrant are mounted aft of the quadrant on the structure beneath the control cabin. Two switches are operated by control column movement in the up-elevator direction; and two, by movement in the down-elevator direction. These switches interrupt electrical commands to the STCMs if the control column is displaced 3.7 to 5.5 degrees from neutral in a direction opposed to the trim. A cam on the elevator forward quadrant operates the switches.
 11. Horizontal Stabilizer Body Seal Doors and Door Mechanisms
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 A.  AIRPLANES WITH UPPER SEAL DOORS AND MECHANISM; There are two upper and two lower horizontal body seal doors, the door mechanisms, and the sliding blade seals.
 (1)  The body seal doors, the door mechanisms, along with the sliding blade seals, serve to provide a weather seal for the horizontal stabilizer center section body cavity. The doors prevent air from flowing through the body cavity and causing excessive drag when the stabilizer is moved up or down.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 27-41-00
 ALL  ú ú 10 Page 10 ú Feb 18/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 (2)  
The body seal doors are hinged to the body and the sliding blade seals are attached to the stabilizer. The door mechanisms are pin connected to fuselage structure and are connected to the body seal doors through drive rods and to the stabilizer through pylon drive masts. When the stabilizer moves up or down, the doors will open and close as required to cover the body cavity caused by stabilizer motion.

 B.  
AIRPLANES WITH FIXED UPPER BLADE SEALS; There are two fixed upper blade seals and two lower horizontal body seal doors. The lower body seal door has the door mechanism and the sliding blade seal.

 (1)  
The fixed upper blade seals are used as a weather seal for the horizontal stabilizer center section body cavity and are attached to the stabilizer.

 (2)  
The lower body seal doors, the door mechanisms, along with the sliding blade seals, serve to provide a weather seal for the horizontal stabilizer center section body cavity. The doors prevent air from flowing through the body cavity and causing excessive drag when the stabilizer is moved up or down.

 (3)  
The lower body seal doors are hinged to the body and the sliding blade seals are attached to the stabilizer. The door mechanisms are pin connected to fuselage structure and are connected to the body seal doors through drive rods and to the stabilizer through pylon drive masts. When the stabilizer moves up or down, the doors will open and close as required to cover the body cavity caused by stabilizer motion.
　
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