What condition must be met to ascertain that you have an adequate interval behind another aircraft?

The condition that needs to be met to determine an adequate interval behind another aircraft involves ensuring that the aircraft ahead has turned at least 90 degrees and is either abeam or behind your wingtip. This criterion is essential for establishing safety in flight operations, especially in training and formation flying scenarios.

When the aircraft ahead has turned at least 90 degrees, it creates a spatial separation that reduces the risk of mid-air collisions. Being abeam or behind your wingtip provides a clear indication that you are not on an intercepting path with the other aircraft and that there is a safe distance between the two. This positioning allows for better visual monitoring of the other aircraft's movements and further enhances safety during maneuvers.

Other options do not sufficiently ensure the required safe distance. For instance, visually confirming the interval with a clear line of sight, while useful, may not provide the same level of assurance in terms of spatial separation as the specific positional criteria of being abeam or in the correct relation to the aircraft ahead. Similarly, reliance solely on traffic collision avoidance systems or maintaining speed equal to or greater than the aircraft ahead does not address the crucial aspect of lateral separation and visual situational awareness that is fundamental to ensuring a safe interval.