What is the phraseology if the primary radar source is out of service?

The phraseology indicating that the primary radar source is out of service is best captured by stating that it is unavailable, but services are still provided for transponder or ADS-B equipped aircraft. This indicates that while traditional radar is not functioning, alternative surveillance methods are still available, allowing air traffic control to maintain situational awareness for those aircraft equipped with transponders or ADS-B.

The inclusion of transponder or ADS-B equipped aircraft suggests that these aircraft can still be monitored, enhancing safety and operational efficiency. This phraseology aligns with standard practices in aviation communication, where it is crucial to inform pilots about the status of radar services while also providing them with relevant information on what alternatives are accessible.

In contrast, options that imply radar services are entirely unavailable do not accurately reflect the operational capabilities when certain technologies are still functional, thus failing to provide the necessary information for pilots depending on surveillance capabilities.