~....................................................................... |ABBREVIATION | DEFINITION | ......................................................................... | VFR | Visual Flight Rules | ......................................................................... | VHF | Very High Frequency | ......................................................................... | VMO (Vmo) | Maximum Operating Airspeed (Knots) | ......................................................................... | VNAV | Vertical Navigation | ......................................................................... | VOR | VHF Omni-directional Range | ......................................................................... | V/S | Vertical Speed | ......................................................................... | XFMR | Transformer | ......................................................................... | XMTR | Transmitter | ......................................................................... | XPNDR | Transponder | ......................................................................... | Y/D | Yaw Damper | ......................................................................... | YD ACT | Yaw Damper Actuator | ......................................................................... | YDM | Yaw Damper Module | ......................................................................... | YDS | Yaw Damper System | 2.............….........................................................1
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
HYDRAULIC AND FLIGHT CONTROLS (AUTOFLIGHT) - DESCRIPTION AND OPERATION
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General
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A. The hydraulic system provides power for many mechanical functions, one of which is to move flight control system control surfaces.
B. The flight crew controls the airplane in pitch, roll, and yaw axes through the flight control system. All flight control surfaces are moved by hydraulic actuators or hydraulic power control packages. The power control packages are controlled either manually or from autoflight system servos.
C. This section provides a general discussion of airplane hydraulic power and flight controls associated with autoflight. For a detail description of airplane Hydraulic Power, refer to 29-00-00/001. For a detail description of Flight Controls, refer to 27-00-00/001.
Hydraulic System (Fig. 1)
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A. Four independent hydraulic systems are installed. Each system has its independent pressurized reservoir, filters, pumps, flow control valves, gages, and sensors. The reservoirs are pressurized by regulated air from the pneumatic system to provide a positive supply of hydraulic fluid to each pump. Rated pressure of each system is 3000 psi. Fire-resistant hydraulic fluid, BMS 3-11 Type IV, is used for protection against fire.
B. Each hydraulic system has an engine-driven pump (EDP) as its primary source of hydraulic power. Hydraulic system No. 1 and No. 4 each has an air-driven pump (ADP) as its demand pump. Hydraulic system No. 2 and No. 3 each has an ac motor-driven pump (ACMP) as its demand pump. Hydraulic system No. 4 has an auxiliary ACMP which provides hydraulic power for brakes during towing operations.
C. Engine-driven pumps are primary pumps which run continuously when they are turned on. Air-driven pumps and ac motor-driven pumps are demand pumps which may be controlled to run only on demand when automatic function is selected.
D. All hydraulic systems have system pressure and temperature sensors. System pressure of each pump is monitored by an independent sensor. System fault indicators and pump pressure indicators on the hydraulic control module provide a means to monitor abnormal conditions.
Flight Control System (Fig. 2)
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