Autorotation

Autorotation is a helicopter flight condition and emergency procedure in which the main rotor keeps turning without engine power because air flows upward through the rotor disc. It is used after an engine failure or loss of drive, and also in training. The pilot lowers collective promptly, controls airspeed and rotor RPM within limits, and uses the flare and landing phase to reduce rate of descent and ground speed. A safe autorotation depends on maintaining rotor energy and making the correct control inputs at the right time.