What is an APU and its role in aviation?

An APU, or Auxiliary Power Unit, serves a crucial role in aviation by providing essential power and air conditioning when the aircraft is on the ground as well as during engine startup. This function is particularly important since it allows the aircraft to operate systems without relying on the main engines, thus conserving fuel and ensuring efficient operation. The APU generates electrical power for starting engines, running onboard systems, and providing environmental control, which includes air conditioning for passengers and crew.

In modern aviation, the APU system enhances operational efficiency and safety by ensuring that various electrical systems and environmental conditions can be maintained without the need for the engines to be running, which is critical during pre-flight preparations and while on the tarmac. This capability is essential to provide comfort and functionality while the aircraft is not in the air.