Obviously, when placed or spawned at altitude, aircraft spawn with their engines on at low thrust. However, they only consider height ATL, and do not check if there is a solid object below them, meaning that aircraft spawning or respawning on the roof of a tall building, offshore platform, dock, certain roadways, etc spawn with their engines on despite being supported. Annoying when you have rooftop helipads generating a lot of noise, and deal-breaking when you have jets throwing themselves off of seaborne runways.