How ADS-B Works

ADS-B Coverage Map
••• Screenshot: FAA

ADS-B is the new air traffic control technology the Federal Aviation Administration (FAA) has adopted. It's a key part of the Next Generation Air Transportation System, which is frequently called just NextGen.

ADS-B uses Global Positioning System (GPS) satellite signals to identify the locations of aircraft. It's far more accurate for air traffic control than the previous, radar-based system.

ADS-B stands for Automatic Dependent Surveillance-Broadcast. It broadcasts aircraft information continuously to air traffic controllers and other participating aircraft. It will enable planes to fly more direct routes, ease congestion, decrease carbon dioxide emissions, and save aircraft operators time and money.

Components

ADS-B has four main components.

  • Satellite constellation: Data is continuously sent from the set of 24 GPS satellites to aircraft's onboard GPS devices, where the data are interpreted and then sent to ADS-B ground stations.
  • Ground-based stations: Some 660 ground-based stations, or ground-based transceivers, in the United States receive data and transmit them to air traffic control stations.
  • Two pieces of equipment that must be installed on aircraft to enable them to broadcast data to ground stations and other properly equipped aircraft: an instrument flight rules-certified, WAAS-enabled GPS receiver and either a 1090 MHz extended squitter (ES) with a Mode S transponder or a 978 MHz universal access transceiver (UAT) for use with an existing transponder. The UAT option is allowed only for aircraft that never fly above 18,000 feet or outside the United States. Some UATs have a GPS receiver incorporated into them.

    How it Works

    ADS-B uses satellite signals and aircraft avionics systems to interpret aircraft data and broadcast it to air traffic controllers on a continuous basis and in almost real-time. Aircraft that have the GPS receiver will also have access to the data, enabling pilots to know the locations of other aircraft.

    The satellite and aircraft avionics data create a very accurate picture of each aircraft's location, speed, altitude, and more than 40 other parameters. These data are transmitted to a ground station and then to air traffic controllers.

    There are two different functions of ADS-B: ADS-B In and ADS-B Out.

    • ADS-B Out is the first and main function that the FAA has addressed. An aircraft that is capable of ADS-B Out can broadcast its data to air traffic controllers and other ADS-B equipped airplanes. According to an FAA mandate, all aircraft that want to fly in airspace that currently requires a transponder must have the WAAS-enabled GPS receiver and either the ES or UAT by January 1, 2020.
    • ADS-B In remains an optional capability. The ADS-B In function will allow aircraft to receive traffic and weather information in real-time on the aircraft cockpit display. ADS-B In is a great improvement over radar-based traffic collision avoidance systems (TCASs). For example, TCASs can display the vertical distance from another aircraft but not the lateral distance. ADS-B In will display the speeds, locations, altitudes, and vectors of other participating aircraft, along with many other pieces of data.

      Limitations and Errors

      The biggest issue for ADS-B is the cost of purchasing and installing the necessary equipment on virtually every aircraft in the country. While the program makes flying safer and more efficient, some corporate flight departments and general aviation pilots are having a difficult time justifying the cost, which may run from about $4,000 to as much as $200,000 depending on the kind of equipment selected and the type of aircraft.

      ADS-B has very few system errors; in fact, it is known for its reliability. No human-made system is fool-proof, though, and some experts claim that ADS-B (and GPS in general) is vulnerable to system infrastructure attacks such as hackers or GPS jamming. Additionally, since ADS-B is reliant on the GPS satellite system, normal satellite-related errors, such as timing errors and those due to disturbances from the ionosphere, can affect the accuracy of ADS-B.