Which altitude is generally associated with radar separation protocols?

The altitude that is generally associated with radar separation protocols is typically FL250. This altitude is significant because below FL290, air traffic control can effectively utilize radar to manage air traffic and maintain safe separation between aircraft. The use of radar allows controllers to monitor aircraft positions more accurately and adjust their flight paths as necessary to ensure safety.

FL400 and FL450 are heights where air traffic becomes less congested and can often be monitored by en route services, but specific separation requirements may also relate to airspace classifications and types of operations occurring at these altitudes. FL350 is an important flight level in some operational contexts but, again, radar capabilities and separation typically become prominent around FL250 in controlled airspaces.

Therefore, the most accurate association with radar separation protocols aligns with FL250, as it represents the threshold where radar control is most commonly emphasized for maintaining effective air traffic management in many areas.