But who knows why there's a hidden extra engine in planes, like this @british_airways A380? 🤔✈️ . Many people don't know this, but most large commercial aircraft have an APU, an Auxiliary Power Unit, which is vital to aircraft operations and ensures a smooth passenger experience, but it doesn't always get used, because more sustainable solutions step in... Let me introduce, an ex-pilot, to explain! . Edits by the @TheJayKnows as always. . #Aviation #BritishAirways #Airport