What must be established before implementing visual separation?

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Visual separation is a method used by air traffic controllers to maintain safe distances between aircraft when they can visually determine their positions relative to each other. Before implementing visual separation, it is essential to establish another form of approved separation. This means that there should be a confirmed separation standard in place, ensuring that the aircraft are at a safe distance from each other before allowing pilots to maintain their own separation based on visual references.

This approach is crucial because it adds an additional layer of safety, particularly in complex airspace where visibility might be compromised, or where there are multiple aircraft in close proximity. The existing approved separation, whether it be through altitude, track, or another method, provides a fallback in case visual separation is not maintained.

Other choices, while they may pertain to safety or operational protocols within air traffic control, do not necessarily establish the necessary groundwork for visual separation. Ground control approval refers to actions taken on the ground rather than in the airspace, a radar backup provides a technological solution rather than the required separation, and separation by altitude, while a kind of separation, would not confirm that visual separation is established in the first place.