Learn to Fly: How it all Works

Automatic Dependent Surveillance-Broadcast (ADS-B)

Imagine one day in the near future looking at a multifunction display (MFD) in your cockpit and seeing virtually the same traffic information as air traffic control. And, the MFD also shows the latest weather in text and graphics. That is the promise that ADS-B — automatic dependent surveillance-broadcast — holds for general aviation (GA), and it is one very large step closer to reality now that the FAA has decided what systems will be used for "linking" the information to aircraft.

The ADS-B system, and others like it being offered by nongovernmental providers, holds great promise for pilots to bring real-time weather, air traffic, temporary flight restrictions (TFRs), and enhanced situational awareness information into the cockpit.

The new technology takes advantage of the Global Positioning System (GPS), a network of satellites that can accurately determine the position of a given object to within 10 meters. The technology determines an airplane's position via GPS then broadcasts that position to all listeners.

The information is transmitted using universal access transceivers (UATs). These UATs use the 978 MHz frequency that can move up to four times as much data at about four times as fast as current datalink methods.

ADS-B-equipped aircraft digitally broadcast their positions derived from the on-board GPS receivers to other ADS-B-equipped aircraft and to ground stations. The information includes position, altitude, airspeed, and projected track, which can then be displayed on an aircraft's MFD or an air traffic controller's screen. Proof-of-concept trials were conducted in Alaska under the name Project Capstone, proved that ADS-B can greatly extend air traffic control's (ATC's) view of all air traffic by using remote ground receivers where air search radars would be impractical and by feeding the remote signals back to the controller's screen.

In the air, the digital data receiver on an ADS-B-equipped aircraft opens up tremendous possibilities. An airborne ADS-B receiver will only be able to display signals from other ADS-B-equipped aircraft. But using a traffic information system-broadcast (TIS-B), ATC will be able to uplink surveillance and en route radar data to the aircraft. In addition, a flight information system-broadcast (FIS-B) will be able to uplink textual and graphical weather information for display on the cockpit MFD.

The Federal Aviation Administration (FAA) could implement the ADS-B in the United States sometime in 2005.