Overrun is a defined drivetrain function

A fictional drivetrain model contains an engine input, reduction gears, a rotor and a freewheeling unit. The diagram states which race is driven in normal powered operation and that the unit permits the rotor to overrun a slower engine. The exercise then reduces engine speed while allowing the rotor to continue rotating. A learner assumes that the engine and rotor must remain rigidly locked because both belong to the same transmission. Another recognizes the specified overrun function. The task asks for the mechanical distinction, not for a control maneuver. No actual helicopter, rotor speed, flight condition or permitted landing procedure is supplied. A suitable answer explains the component's role without claiming that the simple model establishes safe autorotation or a guaranteed restart.