The U.S. Federal Aviation Administration announced the completion of the ground-radio infrastructure for automatic dependent surveillance-broadcast (ADS-B), the surveillance piece of its NextGen ATC modernization effort. Of 230 ATC facilities nationwide, 100 already track aircraft by ADS-B, the agency said.

The FAA awarded Exelis of McLean, Va., the contract to install ADS-B ground radio stations in August 2007. The agency later amended its goal to complete the network by 2013. In an interview with AIN last month, Exelis said that 658 of 660 total ground radio stations will enter service this year, including all 601 the company is installing in the lower 48 states. The FAA measures the network deployment in terms of service volumes, which have a certain number of ground stations associated with them, rather than by ground stations.

Through ADS-B, aircraft equipped with GPS and 1090 MHz “extended squitter” datalink transponders, or general aviation planes with GPS and 978 MHz universal access transceivers, regularly broadcast their satellite-derived position to the ground stations and other nearby ADS-B equipped aircraft. The FAA has mandated that operators in the U.S. equip for that capability, known as ADS-B Out, by 2020. It has not mandated ADS-B In, the ability to display air traffic in the cockpit.

Ground stations receive the ADS-B position broadcasts and pipe the data to ATC facilities, where it is fused with primary and secondary surveillance radar tracks and presented on controller screens. The data is also used to generate traffic information services-broadcast (TIS-B) reports that are uplinked to ADS-B equipped aircraft. ADS-B updates aircraft position once per second, whereas radar updates every 4.7 seconds or longer. The FAA said it expects the system will be “connected and operating” at all 230 ATC facilities by 2019.

Announcing the completion of the ground-station network on April 14, Transportation Secretary Anthony Foxx said: “This upgrade is an important step in laying the foundation for the NextGen system, which provides controllers a much more precise view of the airspace, gives pilots much more awareness and information, and as a result strengthens the safety and efficiency of our system.”