F98675 F98945
Auxiliary Power Unit Component Location 500
49-00 Figure 1 (Sheet 1) Aug 15/67
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500 Auxiliary Power Unit Component Location
Oct 20/83 Figure 1 (Sheet 2) 49-00
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
2. APU Power Plant
A. The APU power plant consists of the APU engine assembly as installed on the airplane (Fig. 1). The APU engine assembly contains the APU engine, ac electrical generator, and the engine mount brackets.
3. APU Shroud
A. The APU engine and its accessories are enclosed in a fireproof and sound reducing shroud (Fig. 1). The shroud consists of the upper shroud and the lower shroud.
4. APU Mounts
A. The APU mounts consist of the ring mounts, shroud rings, and engine mounts. The shroud rings provide support for the engine mounts and for the upper shroud. The shroud rings are attached to the airplane structure with ring mount struts and brackets.
5. APU Air Inlet
A. The APU air inlet provides the compressor inlet air and cooling air to the APU engine. The air inlet consists of the air diffuser duct, compressor air inlet duct, accessory cooling air duct, and the air inlet door (Fig. 1).
6. APU Engine
A. The APU engine is a gas turbine, consisting of a two-stage centrifugal compressor directly coupled to a single-stage inward flow turbine (Fig. 2). The turbine shaft is geared to the accessory drive section and provides power for driving the engine accessories and the generator.
7. APU Fuel System
A. The APU engine fuel system delivers fuel from the airplane tank No. 1 to the APU engine where it is metered and delivered to the combustion chamber (Fig. 2). The fuel system regulates the fuel flow to maintain a constant turbine speed under varying load conditions and to maintain turbine temperatures within the safe zone.
8. APU Ignition and Starting
A. The APU ignition and starting system provides the means of cranking the engine and igniting the fuel-air mixture in the combustion chamber (Fig. 2). Automatic controls de-energize the starter motor and ignition circuits when the engine is rotating at approximately 50% and 95% service speed respectively.
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49-00 Page 4 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 15/77
F99309
558 Auxiliary Power Unit Block Diagram
May 15/77 Figure 2 49-00
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
9. APU Air
A. The APU air system consists of pneumatic and mechanical components, which function automatically, to regulate the rate and maximum amount of bleed air that can be drawn from the APU for use in the airplane pneumatic systems (Fig. 2).
B. A fan driven by the accessory drive section circulates the cooling air to the ac electrical generator, lubricating oil cooler, and engine accessories (Fig. 2).
10. APU Engine Controls
A. The APU engine controls consist of manually and automatically operated switches to control the starting, stopping and normal running of the APU engine. The APU control components are located on the APU engine, in the APU control unit, and on the forward overhead panel (Fig. 1 and 2).
11. APU Engine Indicating
A. The APU engine indicating consists of an exhaust gas temperature indicating system, an elapsed time indicator mounted on the APU for recording the number of hours the APU has been operated, and an overspeed light on the forward overhead panel (Fig. 1).
12. APU Exhaust
A. The APU exhaust is a sound reducing system that directs the APU exhaust gases overboard through an air-cooled exhaust duct (Fig. 1).
13. APU Lubrication
A. The APU lubrication system is a self-contained system that provides pressurized and spray lubrication for all gears and bearings within the unit. It consists of an oil pump, oil tank and various oil lines (Fig. 2).
14. APU Oil Indicating
A. The APU oil indicating system provides means of monitoring the high oil temperature, low oil pressure, and low oil quantity with indicating lights, which are located on the forward overhead panel (Fig. 1).
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