When can arrivals be separated from departures by a minimum of 2 miles in a radar environment?

Separating arrivals from departures by a minimum of 2 miles is based on specific actions during aircraft operations. The rationale for this separation standard hinges on the phase of the departure process.

When the departing aircraft begins its takeoff roll, the aircraft is committed to taking off and is actively in motion down the runway. This phase marks a critical point where the aircraft's trajectory is being established. By ensuring a 2-mile separation at this moment, air traffic controllers can maintain safe distances from an arriving aircraft that may be on a converging path.

During this phase, the aircraft is also in a position where it has begun to gain speed and momentum, which enhances the predictability of its flight path. This becomes crucial in managing both arrivals and departures, allowing for timely adjustments if necessary.

The reference to situations where a departing aircraft is simply cleared for takeoff does not guarantee that it has actually begun moving, which could still create a risk of reduced separation during that transitional period. Similarly, the conditions related to the DME-equipped aircraft or the outer marker concern altitudes and approaches rather than the physical action that establishes safe separation when a departure is fully committed.