An APU, or Auxiliary Power Unit, is an essential part of large transport category aircraft. This device is basically a small engine located in the tail. If you’ve ever seen exhaust out of the tail, that’s the APU running! Uses for the APU include providing electrical power to the aircraft at small airports, providing power to start the engines, and emergency power in flight. In Infinite Flight, this is no different. Because it adds to the realism, the APU is surely an appreciated feature in Infinite Flight.