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This glossary is written for virtual airline and flight simulation use within Virtual Air Canada Airline. It is not intended as a real-world aviation reference.
The Auxiliary Power Unit (APU) is a small gas turbine engine located in the tail section of most commercial aircraft. Its primary roles are to supply electrical power and pneumatic bleed air to the aircraft while it is on the ground, independent of the main engines or external ground power. The APU allows crews to power avionics, cabin lighting, air conditioning, and other systems before engine start, and it provides bleed air to the engine starters. On some aircraft types, the APU can also supply bleed air in flight as a backup source for pressurization if an engine is inoperative. APU operation burns jet fuel and generates noise and emissions. Ground run times are typically governed by airline standard operating procedures and environmental policies to minimize fuel burn, noise impact on airport communities, and carbon output. The APU is started using battery power and is normally shut down once ground power or main engine bleed air is available. Maintenance tracking for APU cycles and hours is separate from the main engines, as the APU accumulates its own service life limits.

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In Virtual Airline Operations

At Virtual Air Canada Airline, the environmental policy limits APU usage to a maximum of 30 minutes while at the gate. This reflects real-world airline sustainability practices aimed at reducing unnecessary fuel burn and emissions during ground operations. Pilots are encouraged to connect to external ground power (GPU) as soon as it is available and to shut the APU down promptly once main engines are running and supplying bleed air.
  • EICAS - Engine Indication and Crew Alerting System
  • CDL - Configuration Deviation List
  • CG - Center of Gravity