When does distance-based wake turbulence separation apply?

Distance-based wake turbulence separation applies specifically when an aircraft is below or crossing behind another aircraft at 1,000' or less. This procedure is crucial for ensuring safety between aircraft, as the effects of wake turbulence can be particularly significant at lower altitudes, where airflow is more disturbed and the proximity of aircraft increases the risk of encountering wake turbulence.

The separation criteria is designed to account for the reduced effectiveness of the wake turbulence mitigation measures when aircraft are closer to the ground and less able to recover from the disruptive forces. Unlike during takeoff or landing, where different separation standards may apply, the emphasis on a specific altitude of 1,000' aligns with operational practices that prioritize safety in high-traffic areas.

The other options do not comprehensively reflect the situations where distance-based wake turbulence separation norms are implemented, as they either apply to incorrect altitudes or restrict the consideration to specific phases of flight rather than addressing the critical aspect of altitude and proximity behind another aircraft.