Which scenario is most likely to cause the onset of Vortex Ring State?

Vortex Ring State, also known as "settling with power," occurs when a helicopter descends into its own rotor wash, leading to an unstable flight condition. The correct scenario that most likely causes the onset of Vortex Ring State involves a combination of zero forward airspeed, significant descent rate, and the application of power.

In the chosen scenario, the helicopter experiences zero airspeed with power applied and is descending at a rate greater than 400 feet per minute. This scenario is particularly prone to Vortex Ring State because the helicopter is not moving forward, which means the rotor system is not generating effective lift relative to the airflow, but rather descending rapidly. The high descent rate induces the rotor blades into their own downwash, creating vortices that can further disrupt the airflow over the rotor system. When these conditions occur, the helicopter can quickly lose lift, leading to a potential loss of control.

In contrast, the other scenarios present either lower descent rates or insufficient descent conditions that do not facilitate the same buildup of vortices in the rotor wash, thus reducing the likelihood of entering Vortex Ring State. Scenarios with lower descent rates or slight forward speed are less likely to produce the same critical conditions necessary for the onset of this dangerous state.