If you know what the APU is, feel free to give me extra info on what it does:) For all that don’t, then fear no more!
History of the APU:
The first commercial jetliner with an APU was the Boeing 727, which debuted in 1964. Before that, planes used APU’s that were attached to trucks, making the engine starting process longer.
Let’s back up a bit. APU stands for the Auxiliary Power Unit. The APU is a small jet engine under the tail that supplies electricity and air conditioning when both of the plane’s engines are not running. All types of modern airliners have an APU. Besides providing electricity and air conditioning in emergency situations, it also provides high-pressure air needed for starting the main engines. This is needed because the internal batteries on larger aircraft aren’t powerful enough to initially rotate the engine’s compressors. It also provides comfort to passengers boarding when the engines aren’t on. Some airports limit the use of APU’s for sound purposes, and use ground power to start the engine. The APU is critical because it gives backup power in emergency situations, making planes slightly safer. So whenever you hear a hissing noise like 1000 hairdryers while boarding the plane, don’t fear, the APU is here.