So far, it’s been 9 years and counting without a fatal accident for a US carrier.

These facilities are responsible for controlling aircraft en route in a particular volume of airspace (a Flight Information Region) at high altitudes between airport approaches and departures, while the towers just control the airport’s airspace.

These are radar installations that are within 30-50 nautical miles of an airport that work with towers and Route Traffic to direct planes.

For inter-airport, as well as across various airports – dedicated lines so that airports don’t need to rely on outside telecommunications utilities.