Under what conditions are aircraft established on radials of the same NAVAID considered laterally separated?

Aircraft established on radials of the same NAVAID are considered laterally separated when either aircraft is beyond the protected airspace for the other. This is based on air traffic control procedures that ensure safe distances are maintained between aircraft operating in close proximity to each other.

The protected airspace around a radial is determined by specific lateral dimensions that ensure that even if an aircraft deviates slightly from its intended flight path, it will not conflict with another aircraft flying on a different radial or heading. When one aircraft is positioned outside this protected airspace of another, it guarantees safe lateral separation, allowing for safe operation even if they are at the same altitude or flying on similar paths.

The other options provided do not inherently ensure lateral separation: different altitudes do not provide separation if the aircraft are close enough vertically to pose a risk, the same speed does not imply separation, and varying flight routes do not automatically guarantee that the aircraft will remain laterally separate unless they are also positioned appropriately relative to one another.