How It Works: ADS-B

The GPS-based system determines highly accurate position and groundspeed information, and relays it to ATC and other ADS-B-equipped aircraft.

Automatic dependent surveillance-broadcast is a GPS-based system meant to replace the traditional radar-based technology ATC has relied on for decades to detect and manage aircraft traffic.

Accuracy and Efficiency

ADS-B relies on an aircraft’s GPS receiver to determine highly accurate position and groundspeed information, which it calculates by receiving radio signals from a network of satellites and comparing the time stamp of when those signals were sent with the time stamp of when they are received.

Aircraft then take this GPS data and, along with identification and flight-status information, transmit it to ground-station receivers using a datalink transmitter in the form of either a Mode S transponder or a universal access transceiver. This occurs automatically a minimum of once every second, compared with the existing radar-based system, which scans for data once every five to 12 seconds, thus providing a much more accurate picture of the traffic landscape at any given time to ATC. According to the FAA, this change will allow ATC to reduce separation between aircraft and implement more efficient routing.

But this information isn’t just transmitted to ATC; it is also shared among aircraft. Aircraft with ADS-B In capabilities can receive this information either directly from other aircraft or via the ground stations, which re-broadcast it along with position data for non-ADS-B-equipped aircraft that have a transponder and are within radar coverage. UAT-equipped aircraft can also receive subscription-free weather.