When should an aircraft be informed that radar service is terminated?

An aircraft should be informed that radar service is terminated when it proceeds into a non-radar coverage area. This is crucial because radar service is dependent on the availability of radar signals from ground stations. Once an aircraft enters an area where radar coverage is no longer available—due to terrain, distance from the radar facility, or other factors—it can no longer be effectively monitored through radar systems. Notifications of termination are essential to ensure pilots are aware that they are transitioning to non-radar operations, which means they will need to rely on other means of navigation and communication for their flight.

This understanding helps maintain safety and operational awareness for both pilots and air traffic controllers, as it sets expectations for the limitations on radar services that will follow the transition into these areas.