Tyson once said on twitter “An airplane whose engine fails is a glider. A helicopter whose engine fails is a brick.” Now it's not at all obvious why that's not true. But that's why it's important to be humble about what you do and don't know.
> Autorotation is the ability of a helicopter to in some situations have its rotors powered by the flow of air rather than the engine. In short, as the helicopter descends, the upward directed flow of air pushes through the rotors, makes them rotate faster, which in turn provides lift.
see the "dead man's curve" which relates to having an engine failure with insufficient height or lateral speed (helicopters shouldn't hover in place unless a good ways up) https://en.wikipedia.org/wiki/Helicopter_height%E2%80%93velo...