What flight condition is indicative of a tail rotor vortex ring state?

In helicopter flight dynamics, a tail rotor vortex ring state typically occurs when the helicopter experiences an uncontrolled descent. This condition is characterized by a significant loss of tail rotor effectiveness, which can be caused by the turbulent airflow generated from the main rotor and the resulting interaction with the tail rotor.

As the helicopter descends without sufficient forward airspeed or in a high-power setting, the tail rotor may enter a region of disturbed air where it cannot produce enough thrust to counteract the yawing motion induced by the main rotor's torque. This can result in a loss of control, making it difficult to maintain directional stability. As such, recognizing and understanding how an uncontrolled descent correlates with tail rotor vortex ring state is vital for a pilot’s safety and operational effectiveness.

Each of the other options describes flight conditions that do not typically lead to vortex ring state in the tail rotor. Quick ascent with stable rotor RPM suggests controlled flight, while sustained hover may imply a stable environment with adequate tail rotor effectiveness. Over-speeding of the rotor refers to excessive rotor RPM that might occur under specific conditions unrelated to vortex ring states.