What distance must be maintained when separating aircraft below FL600?

When separating aircraft below Flight Level 600 (FL600), the standard distance that must be maintained is 5 miles. This separation requirement is crucial for ensuring safety in the airspace, as it helps to prevent potential collisions between aircraft. The 5-mile standard is widely recognized and utilized in air traffic control procedures.

The reason this specific distance is established is due to the operational characteristics of aircraft at lower altitudes. The relative speeds and maneuverability at these altitudes necessitate a buffer that accommodates both vertical and horizontal separation.

In comparison, other distances provided in the options, like 3 miles, 7 miles, and 10 miles, are not applicable for this specific flight level under typical conditions. The 3-mile separation is often applied to different traffic scenarios, while 7 miles and 10 miles would create unnecessarily large safety buffers at lower altitudes, potentially reducing airspace efficiency without a corresponding increase in safety.