Page 5 D633W101-BEJ Sep 05/2002
AUXILIARY POWER SYSTEM -GENERAL DESCRIPTION
APU Air System
The APU air system supplies pressurized air to the airplane pneumatic system. Inlet guide vanes control the amount of air supplied to the load compressor. A surge control valve releases excess bleed air overboard. An eductor removes APU compartment air by suction through the oil cooler to cool engine oil.
APU Indicating System
The APU indicating system supplies APU EGT data for flight deck display. A data memory module keeps APU operation data.
APU Exhaust System
The APU exhaust system sends the APU exhaust gasses out of the left side of the tailcone.
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AUXILIARY POWER SYSTEM -GENERAL DESCRIPTION
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AUXILIARY POWER SYSTEM -INTERFACES
General
The APUC gets airplane system data and sends APU data to airplane systems through the left and right system ARINC 629 data buses. The APUC also sends and receives some data through other connections.
ARINC 629 Interfaces
These systems have interfaces with the APUC through systems ARINC 629 buses:
*
Bus power control unit (BPCU) -generator trim frequency
*
APU generator control unit (GCU) -generator load
*
Left and right air supply cabin pressure controller (ASCPC) -pneumatic valve positions, pack operation, and pneumatic duct pressure
*
Left and right engine data interface unit (EDIU) -engine data
*
Left and right cabin temperature controller (CTC) -pneumatic valve position and ECS data
*
Left and right overhead panel ARINC 629 system (OPAS) -overhead panel switch/selector positions
*
Left and right weight on wheels (WOW) cards -air/ground condition
*
Hydraulic interface module (HYDIM) cards -ADP operation data
*
Fire overheat detection card (FODC) -APU fire
*
Left, right, and center duct leak and overheat detection system (DLODS) -wing/body duct overheat
*
Electrical load management system (ELMS) -start control, shutdown control, autostart, attended/unattended mode
* Airplane information management system (AIMS) engine running status, air data (from ADIRU), airplane data, fault reporting, indications.
Other Interfaces
The APUC also has hardwire interfaces with these systems and components:
*
Electrical load management system (ELMS)
*
APU selector
*
APU maintenance switch
*
APU inlet door switch
*
APU fire switch and fire shutdown switch
*
Fire overheat detection card (FODC)
*
APU generator OFF light
*
APU fault light.
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777 AIRCRAFT MAINTENANCE MANUAL
AUXILIARY POWER SYSTEM -INTERFACES
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AUXILIARY POWER SYSTEM -COMPONENT LOCATIONS
General
The APU is in the tailcone at a 10 degree nose down attitude in relation to the tail of the airplane. A titanium firewall isolates the APU compartment from the rest of the airplane.
Ducts
The air inlet is on the top, right side of the fuselage behind the rudder. The APU exhaust gases exit on the left side of the tail fairing.
Doors
Two APU access doors on the bottom of the APU compartment permit service and maintenance access.
APU Controller
The APU controller (APUC) is in the E7 rack in the ceiling of the aft cabin.
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AUXILIARY POWER SYSTEM -COMPONENT LOCATIONS
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AUXILIARY POWER SYSTEM -APU GENERATOR
General
The APU generator is a secondary source of electrical power for airplane systems. It can supply 120 kva of ac electrical power when the airplane is on the ground or during flight. See chapter 24 for more information on the electrical system.
The APU generator attaches to the accessory pad of the APU gearbox.There is a seal plate between the APU generator and the APU gearbox.
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