What are the necessary preconditions for settling with power to occur?

The conditions for settling with power involve specific parameters of airspeed and descent rate, particularly related to effective translational lift (ETL) and the helicopter's power performance. When the airspeed is at or below ETL, the helicopter experiences decreased lift efficiency due to the lack of effective airflow over the rotor blades.

Settling with power typically occurs in situations where the helicopter cannot maintain adequate lift while descending, which is exacerbated by a descent rate that is too high. When the airspeed is at or below ETL with a descent rate of 300 feet per minute, the rotor system may not generate sufficient lift to counter the descent, especially if combined with high power settings. This situation increases the likelihood of falling into the settling with power condition, as the helicopter becomes increasingly reliant on power to maintain altitude.

The correct choice highlights the critical dynamics of helicopter flight, emphasizing the importance of managing descent rates when operating below ETL. Understanding these preconditions is crucial for pilots to avoid dangerous flight situations and to ensure safety during hovering and low-speed flight.