An Auxiliary Power Unit, or APU, is essential for aircraft operations. It allows planes to function independently, without needing ground support equipment like power units or air-conditioning units. Typically, you’ll find the APU as a small jet engine located in the tail cone of the aircraft. In some models, it can be found in the engine nacelle or wheel well. The APU starts using just the aircraft’s batteries. Once it’s running, it provides electrical power to various systems and supplies bleed air for air conditioning and engine starts.
When an APU is certified for flight use, it becomes even more valuable. It can act as an additional power source if an engine generator fails. Moreover, it can supply bleed air to assist with engine relights during flight or to run the air-conditioning packs when conditions or company rules require the engine bleed to be turned off. This capability is particularly useful in hot and high operations, ensuring that aircraft remain functional and comfortable under varying circumstances.
