What does a single code every 30 seconds on a VOR indicate?

A single code being transmitted every 30 seconds on a VOR signal indicates that while the VOR itself is not operational, the Distance Measuring Equipment (DME) associated with it is still functioning. This scenario typically occurs when there are issues with the VOR, preventing it from providing the usual navigational guidance, but the DME can still accurately measure distance from the station. The continuous transmission of the code serves as an indication for pilots that while they cannot rely on the VOR for directional navigation, they can still get distance information from the DME.

Often, maintenance or operational status updates are signaled in this manner to ensure pilots are aware of the equipment's condition. This information is crucial for flight planning and navigation, allowing pilots to adjust their routes and navigation methods accordingly.