CHAPTER
49
Airborne Auxiliary Power
49-CONTENTS
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AUXILIARY POWER SYSTEM -INTRODUCTION
Purpose
The AlliedSignal Engines 331-500 gas turbine APU supplies the auxiliary power system with electric and pneumatic power. This permits airplane systems to operate independently of ground external power sources or the main engines. Auxiliary power is also available in the air.
Operating Limits
The APU generator supplies 120 KVA electrical power at any altitude. Pneumatic pressure is available up to an altitude of 22,000 feet (6700 m).
Specifications
The dimensions and weights shown do not include the air inlet duct, the exhaust duct, and the APU generator.
Abbreviations and Acronyms
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ADIRU -air data inertial reference unit
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ADP -air-driven pump
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AIMS -airplane information management system
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APU -auxiliary power unit
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APUC -auxiliary power unit controller
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ARINC -aeronautical radio, inc.
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ASCPC -air supply and cabin pressure controller
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ATS -air turbine starter
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ATSCV -air turbine starter control valve
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BPCU -bus power control unit
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CTC -cabin temperature controller
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DLODS -duct leak and overheat detection system
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DMM -data memory module
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dr -door
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ECS -environmental control system
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EDIU -engine data interface unit
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EGT -exhaust gas temperature
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EHSV -electrohydraulic servo valve
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ELMS -electrical load management system
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FODC -fire overheat detection card
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GCU -generator control unit
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HYDIM -hydraulic interface module
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IGV -inlet guide vanes
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LVDT -linear variable differential transformer
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LRU -line replaceable unit
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MFD -multi-function display
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OPAS -overhead panel ARINC system
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PPM -pounds per minute
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PSI -pounds per square inch
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PSIA -pounds per square inch absolute
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PSID -pounds per square inch differential
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PSIG -pounds per square inch gage
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RPM -revolutions per minute
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RVDT -rotary variable differential transformer
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SCV -surge control valve
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SHP -shaft horsepower
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S/O -shutoff
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temp -temperature
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WOW -weight on wheels
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777 AIRCRAFT MAINTENANCE MANUAL
AUXILIARY POWER SYSTEM -INTRODUCTION
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AUXILIARY POWER SYSTEM -GENERAL DESCRIPTION
General
The APU system contains these subsystems:
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APU control system (49-60)
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APU power plant (49-10)
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APU engine (49-21)
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APU and generator lubrication system (49-27)
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APU oil indicating system (49-94).
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APU engine fuel system (49-30)
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APU ignition/starting system (49-40)
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APU air (49-50)
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APU indicating system (49-70)
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APU exhaust system (49-80).
APU Control System
An APU controller controls APU system functions and is an interface with other airplane systems.
APU Power Plant
The APU is a single shaft gas turbine engine which drives an electric generator and a load compressor. A gearbox on the front of the APU supplies power to APU accessories.
The power plant has these systems and components:
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Auxiliary power unit
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APU mounts
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APU wire harness
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APU air inlet
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* APU drains.
APU Engine
The APU engine has a two stage centrifugal flow compressor, a reverse flow annular combustion chamber, and a three stage axial flow turbine.
APU and Generator Lubrication System
The APU and generator lubrication system lubricates and cools the APU bearings, the gearbox, and the electric generator.
APU Oil Indication System
The oil indication system supplies APU oil temperature, pressure, and quantity for flight deck display.
APU Engine Fuel System
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