What is the appropriate separation minima using ASR or DTAS when within 40 miles from the radar antenna?

The appropriate separation minima using ASR (Airport Surveillance Radar) or DTAS (Digital Terminal Automation System) when within 40 miles from the radar antenna is 3 miles. This standard is established to ensure that aircraft are adequately separated to maintain safety and prevent incidents in terminal airspace where traffic density is typically higher and aircraft are maneuvering for landing or takeoff.

Maintaining a separation of 3 miles helps to account for the radar's limitations and ensures that any possible errors in tracking or flight path deviations are mitigated. This distance is deemed safe for the operational environment surrounding airports, where quick responses and precise navigation are crucial.

Shorter distances like 1 mile, while useful in some contexts, may not provide the necessary buffer in busy terminal airspace where operational complexities increase. Similarly, greater distances such as 5 miles or 10 miles may be excessively cautious, potentially limiting airport throughput and not reflecting the actual safety margins needed when radar systems are operating optimally.