What configuration must be established for steep approaches no later than 3 nm from the runway?

For steep approaches in the King Air 350, the correct configuration to be established is when both engines are operative, the flaps are fully extended, the prop levers are in the full forward position, and the approach speed should be either Vref or Vref+15 in icy conditions. This configuration is critical for ensuring sufficient lift and control during the steep approach, which is more demanding than a standard approach.

In this scenario, setting both engines operatively provides the necessary thrust to manage the descent rate while maintaining good control of the aircraft. Using full flaps maximizes lift at lower speeds, allowing for a steeper descent slope without stalling. The full-forward position of the prop levers helps maintain effective propeller efficiency, crucial for performance during the critical phases of approach and landing.

Adjusting to either Vref or Vref+15 in an icing condition ensures that the aircraft has adequate margin over stall speed while accommodating any additional drag that may come from ice accumulation. This is vital for safety when managing a steep descent, where the typical speed margins can be more acute.

In contrast, the other options do not align with the required operational limitations for a safe steep approach in this aircraft.