What is the correct separation distance for an aircraft when under radar separation and it is 40 miles or more from the radar antenna?

When an aircraft is under radar separation and it is 40 miles or more from the radar antenna, the correct separation distance is 5 miles. This standard distance is established to ensure safety and effective management of air traffic in radar-controlled airspace. The 5-mile separation provides a buffer that accounts for potential inaccuracies in radar tracking and ensures that aircraft maintain safe distances from each other, reducing the risk of mid-air collisions and allowing for appropriate response time in case of unexpected events.

In contrast, the other separation distances mentioned would not be adequate at that range. A 1-mile separation might be suitable at shorter distances or under specific conditions where aircraft are closer and have established lower risk levels, but as aircraft distance increases, a larger separation is required to ensure safety in more complex air traffic situations. Similarly, 2 miles and 3 miles may not provide the necessary safety margin when the aircraft are farther from the radar antenna. Therefore, 5 miles is the established standard for aircraft operating at a distance of 40 miles or more from the radar source.