auxiliary power unit
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Related to auxiliary power unit: Ram air turbine, Ground Power Unit
auxiliary power unit[ȯg′zil·yə·rē ′pau̇·ər ‚yü·nət]
A power unit carried on an aircraft or spacecraft which can be used in addition to the main sources of power. Abbreviated APU.
auxiliary power unit (APU)
A power generation unit for operation of systems like hydraulic, air conditioning, electrical, and avionics. It may provide AC (alternate current) or DC (direct current) supply. The APU is normally used prior to starting the aircraft and for testing systems on the ground. In rare cases, it can provide some thrust in an emergency. Ground auxiliary power units provide current for starting engines. See airborne/auxiliary power unit.