9.  Operation
_________
 A.  Static air enters the compressor air inlet plenum. The air is then guided to the power and load compressors. Air entering the power compressor is compressed and enters the combustor. In the combustor, fuel is added and the air-fuel mixture is ignited. The gases of combustion flow through the power and load turbines where the gas energy is converted to mechanical power. The mechanical power is used to drive the power and load compressors as well as the accessory and load gearboxes. Air from the inlet plenum also enters the load compressor and diffuser duct. From here bleed air for airplane pneumatic systems is obtained through the bleed valve.
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747-400
MAINTENANCE MANUAL

LOAD
POWER
COMPRESSOR
SECTION
INLET

GEARBOX PUMP
FUEL METERING ADAPTER
APU Engine Cross Section and Flow Diagram
Figure 1

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747-400 MAINTENANCE MANUAL
 APU ENGINE - INSPECTION/CHECK
_____________________________
 1.  General_______
 A.  This procedure has these tasks:
 (1)
A borescope inspection of the APU

 (2)
A gasket inspection of the load compressor diffuser duct.

 B.  
A borescope inspection of the APU does an inspection of the hot section, compressor areas, combustion chamber and cooling fan of the APU. You can do this task with the APU installed in the airplane or installed in the ground support equipment. A gasket inspection of the load compressor diffuser duct does a check for air leakages around the two flanges and has the necessary steps to repair a section of the damaged gasket.

 C.  
The borescope assembly (PWC 41490) has a flexible fiberscope, a light source, an eyepiece shield, a camera adapter, a side view adapter, and other components. The rigid guide tubes let you get access to the different APU components. A fixture (PWC 41393) is used to hold the flexible borescope in a stable position during the inspection.

 D.  
The borescope access ports are on the two sides and the bottom of the APU engine. You can get access to the borescope ports through the APU access doors.

 TASK 49-21-00-206-012
 2.  APU Borescope Inspection________________________
 A.  Special Tools and Equipment
 (1)  
PWC41490 - Borescope, Pratt & Whitney Canada, Longueuil, Quebec, Canada

 (2)  
PWC41325-001 - Puller, Pratt & Whitney Canada, Longueuil, Quebec, Canada

 (3)  
PWC41491 - Guide Tube, Pratt & Whitney Canada, Longueuil, Quebec, Canada

 (4)  
PWC41492 - Guide Tube, Pratt & Whitney Canada, Longueuil, Quebec, Canada

 (5)  
PWC41493 - Guide Tube, Pratt & Whitney Canada, Longueuil, Quebec, Canada

 (6)  
PWC41494 - Guide Tube, Pratt & Whitney Canada, Longueuil, Quebec, Canada

 (7)  
PWC41495 - Guide Tube, Pratt & Whitney Canada, Longueuil, Quebec, Canada

 (8)
PWC41350 - Puller, Pratt & Whitney Canada, Longueuil, Quebec, Canada

 (9)
PWC41416 - Puller, Pratt & Whitney Canada, Longueuil, Quebec, Canada

 (10)
 PWC41393 - Holding Fixture, Pratt & Whitney Canada, Longueuil, Quebec, Canada

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