Autoraotion occurs when the relative wind is used to turn the rotor blades. Under normal flight conditions, the rotor system is powered by the engine. If the engine fails, a special clutch will disconnect the rotor system from the engine in order to allow the rotors to continue spinning. The helicopter blades will use the upward flow of the relative wind to glide to the ground.
Students must practice autorotations in order to gain certification. The purpose of practicing this procedure is to learn how to safely land the helicopter incase of engine failure.