How is the separation minima altered for ASR-9 and ASR-11 at distances less than 60 miles from the radar antenna?

In the context of radar separation minima for the ASR-9 and ASR-11 systems, the separation minima at distances less than 60 miles from the radar antenna is designed to ensure safe operational procedures for air traffic. The correct answer indicates that this minima remains at 3 miles, which is a standard operational practice to maintain a safe distance between aircraft in terminal airspace where radar coverage and accuracy can be maximized.

The decision to maintain a 3-mile separation at shorter distances considers radar detection capabilities, potential error margins, and the increased density of air traffic near airports. This consistency in minima allows air traffic controllers to manage aircraft safely, even as they approach the radar's short-range limits.

The other choices suggest alterations to this standard, either by reducing or increasing the separation, which could potentially compromise safety or operational efficiency. Maintaining this separation minima thus reflects industry standards and best practices for ensuring safe aircraft operations in proximity to radar systems.