What is ADSB?
ADS-B is a broadcast surveillance system in which an aircraft automatically transmits to a ground station and other air traffic its identity, precise location, altitude, velocity and other information. The system requires an aircraft to be fitted with systems such as a barometric encoder and global navigation satellite system (GNSS) equipment. While ADS-B is required only for aircraft operating under instrument flight rules (IFR), it also offers substantial benefits for visual flight rules (VFR) pilots.
ADS-B ground stations comprise a receiver unit, an antenna and a site monitor. Ground stations across Australia are connected to the Airservices Australia digital communication infrastructure and, combined with radar, provide continent-wide, line-of-sight surveillance coverage above 30,000 ft, as well as significant coverage at lower levels.
ADS-B uses the same transponder as, but operates independently of, the aircraft radar and traffic collision alerting and avoidance (TCAS) systems. Most modern Mode S secondary surveillance radar (SSR) transponders are capable of transmitting SSR and ADS-B (also termed extended squitter) data. However Mode A/C and some older Mode S transponders do not support ADS-B.
Australia, Europe, the US, and the rest of the world have implemented ADS-B on the Mode S frequency band of 1090 MHz—most commonly called ten-ninety ES (extended squitter). In the USA, the FAA has deployed a redundant ADS-B system on 978 MHz called universal access transponder (UAT) for aircraft that operate below 18,000 feet. This system is not deployed in Australia and the avionics will not work—when importing an aircraft from the US, ensure it has the correct ADS-B equipment on board.
ADS-B transmission and display
On-board ADSB equipment can consist solely of a transmission system to send ADS-B information (ADS-B OUT). Aircraft can also be equipped with ADS-B IN—a cockpit display of traffic information (CDTI).
An ADS-B transmitter enables the identity, position and altitude of an aircraft to be determined and displayed to an air traffic controller. The signal is broadcast from the aircraft approximately every half second and, provided the aircraft is within the coverage volume of an ADS-B ground station, the data can be fed to the ATC facility and used to provide air traffic services.