What is the appropriate separation of an aircraft from the edge of the radar area when radar separation is applied at a distance of less than 40 miles?

When applying radar separation at a distance of less than 40 miles, the appropriate separation distance is indeed 3 miles. This distance ensures that sufficient separation is maintained between aircraft to prevent loss of separation in the event of any unforeseen circumstances, such as changes in flight paths or speeds. The 3-mile separation is a standard practiced within air traffic control under these conditions, balancing the need for safety with the operational requirements of managing air traffic efficiently.

Maintaining a separation of 3 miles provides adequate buffer space that accommodates not only the inherent uncertainties of radar tracking but also allows for any adjustments that may need to be made in real-time due to communications with pilots or other air traffic control directives. This is particularly important in busy airspace where multiple aircraft may be in close proximity.

Other distances, such as 1 mile, 2.5 miles, or 4 miles, do not align with the established guidelines for radar separation at this range, which is rooted in ensuring a robust safety margin for managing aircraft in proximity to one another.