Description and Operation
APU Engine Thermocouple Harness Balancing Resistor
Exhaust Gas Temperature Indicator
Exhaust Gas Temperature Balancing Resistor
Exhaust Gas Temperature Thermocouple Probe
Adjustment/Test
Exhaust Gas Temperature Indicator........................................................................ 49-71-12 Removal/Installation
Exhaust Gas Temperature Thermocouple Probe.................................................... 49-71-21 Removal/Installation Adjustment/Test
APU INDICATING SYSTEM ....................................................................................... 49-72-0
Description and Operation
Elapsed Time Indicator
Overspeed Light
Elapsed Time Indicator ............................................................................................ 49-72-11 Removal/Installation
EXHAUST
APU EXHAUST SYSTEM........................................................................................... 49-81-0
Description and Operation
Aft Fairing
Exhaust Duct
Exhaust Duct Muffler................................................................................................ 49-81-11 Removal/Installation Inspection/Check Cleaning/Painting
Exhaust Duct Heat Shield........................................................................................ 49-81-21 Removal/Installation
Aft Fairing................................................................................................................. 49-81-31 Removal/Installation Subject Subject No.
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May 01/98 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Contents 49 Page 5
OIL
APU LUBRICATION SYSTEM.................................................................................... 49-91-0
Description and Operation
Oil Cooler
Oil Pump
Oil Tank
Oil Pump .................................................................................................................. 49-91-11 Unit Servicing
Filter Element Replacement
Removal/Installation
Adjustment/Test
Inspection/Check
Oil Tank.................................................................................................................... 49-91-31 Unit Servicing Removal/Installation
Oil Cooler ................................................................................................................. 49-91-41 Removal/Installation
Oil Pump Drive Shaft Seal ....................................................................................... 49-91-51 Removal/Installation
Oil Tank Vent Line ................................................................................................... 49-91-61 Inspection/Check
APU OIL INDICATING SYSTEM ................................................................................ 49-94-0
Description and Operation
High Oil Temperature Light
Low Oil Pressure Light
Low Oil Quantity Light
Oil Level Switch
Oil Level Switch ....................................................................................................... 49-94-11 Removal/Installation
Oil Temperature Switch ........................................................................................... 49-94-21 Removal/Installation
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Contents 49 Page 6 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 15/78
AIRBORNE AUXILIARY POWER - DESCRIPTION AND OPERATION
1. General
A. The airborne auxiliary power is obtained from a gas turbine auxiliary power unit (APU). The APU is a compact, self-contained unit that provides compressed air for engine starting on the ground. The unit provides compressed air for air conditioning while the airplane is on the ground and at limited altitude in flight. The unit also provides electrical power for use on the ground or in flight.
B. The APU consists of a gas turbine engine, an ac electrical generator driven by a turbine through an accessory drive, and controls for safe and continuous operation. An engine compressor bleed system is connected to the airplane pneumatic system. Refer to Chapter 36, Pneumatic System. The generator provides electrical power for airplane electrical system. Refer to Chapter 24, AC Generation System. Fire detection, warning and extinguishing systems are also provided for the APU. Refer to Chapter 26, Fire Protection.
C. The APU is located in a compartment in the tail section of the airplane (Fig. 1). Access to the APU is obtained through a latched access door in the fuselage directly below the APU.
D. Fuel for the operation of the APU is obtained from fuel tank No. 1 (Fig. 2). Electrical power for starting the APU is obtained from airplane battery. Positioning the master switch to START initiates automatically controlled operations to start the APU. The APU fuel valve and air inlet door opens. Acceleration, ignition, and starter motor cutout are controlled to allow the engine to reach service speed quickly and safely. As soon as the APU attains the service speed, pneumatic or electrical power is obtained by properly positioning the controls. If large amounts of pneumatic power are required, such as for airplane engine starting, the electrical load must be reduced.
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