In the context of air traffic control, what does "separation" refer to?

Separation in air traffic control refers specifically to the minimum distance required between aircraft to ensure safe operation and to avoid collisions in the airspace. This concept is essential to maintaining safety in aviation, as it determines how close two aircraft can be without putting them at risk of encountering each other.

Effective separation allows air traffic controllers to manage multiple aircraft flying in the same vicinity, whether in the air or on the ground, and includes considerations of horizontal separation (lateral distance between aircraft) and vertical separation (altitude difference). This principle is foundational to ensuring safe navigation and operations within crowded airspace environments.

The other options describe related operational aspects of air traffic management but do not define "separation" in the specific context required. For instance, the time intervals between departures and altitude restrictions are crucial for the overall coordination of air traffic but do not directly address the spatial distance required to prevent collisions. The number of aircraft allowed in a flight pattern pertains to capacity rather than the safety distance that defines separation.