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EXCESSIVE LEAKAGE IS NOTED - Replace APU.
NOT OK - Clean vent orifice.
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APU POWER PLANT - DESCRIPTION AND OPERATION
1. General
A. The APU power plant is located in a compartment in the tail section of the airplane. The power plant consists of the engine assembly as installed on the airplane. The APU engine is covered in section 49-21-0. This section provides general information of the power plant and the operation of the APU system.
B. The power plant is enclosed in a sound reducing, fireproof shroud. The shroud consists of two parts: the lower shroud and the upper shroud. The shroud is covered in Section 49-12-0. The upper shroud is mounted in the APU compartment to the shroud rings. The APU engine is also attached to the shroud rings with engine mounts. The ring mounts, shroud rings, and engine mounts constitute the APU mounts, and are covered in Section 49-13-0. Air supply to the APU is provided through the air inlet door and ducts as described in Section 49-15-0.
C. Maintenance of the power plant does not require removal of the unit from the airplane. For the engine maintenance, it is required to open the APU access door in the fuselage and to remove the lower shroud. This provides access to the ac electrical generator, engine accessories, accessory cooling system components, turbine exhaust port, combustion chamber, ignition system, oil tank, and oil lines. AC electrical generator removal is, however, simplified when the power plant is lowered on an aero stand. The lubricating oil can be replenished by opening the APU access door. This provides access to the oil tank filler port and cap.
D. The APU power plant is designed for quick removal and installation. To remove the power plant, it is required to open the APU access door and remove the lower shroud. The unit is removed vertically downward using a special tool.
2. Operation
A. Power for the APU control circuit is 28 volts dc, obtained from the hot battery bus or from the APU generator control unit transformer-rectifier. During the APU start only hot battery bus power is available. The transformer-rectifier power is used as a backup in event the battery bus power is lost while the APU is operating. The APU starter motor obtains 28-volt dc power directly from the airplane battery (Fig. 1). A dc power supply can be used to provide power to both the starter and the hot battery bus in the event of a discharged battery. The external dc power supply receptacle is located together with the external power and battery charger circuit breakers inside the forward body equipment door on the J9 battery shield.
(1)
To connect external power:
(a)
Open battery charger and external power dc circuit breakers.
(b)
Connect 24- to 28-volt dc external power supply cart.
