What is autorotation in a helicopter?

• A. The aerodynamic force that causes a helicopter rotor to spin with no engine power applied to the rotor system.
• B. A flight condition in which the rotor remains powered by the engine while the helicopter descends.
• C. A condition of rotor blade stall during descent.
• D. A procedure for starting the rotor while already in flight.

Answer: (B)

Autorotation is when the rotor blades are driven by aerodynamic forces from the air flowing through the rotor, not by engine power. In a power-off descent (or after an engine failure), the engine is disengaged from the rotor, often via a freewheel mechanism, so the rotor continues turning because air moving upward through the rotor disc keeps it spinning. This allows the helicopter to maintain rotor speed and descend controllably, enabling a safe landing. The idea that the rotor remains powered by the engine while descending describes a powered descent, which is not autorotation. Rotor blade stall is a separate issue related to blade aerodynamics, and starting the rotor in flight is a different procedure altogether.