Science Fair Project Encyclopedia
Automatic Dependent Surveillance-Broadcast
--126.96.36.199 01:36, 19 Apr 2005 (UTC)Automatic Dependent Surveillance-Broadcast (also called ADS-B) is a system by which airplanes constantly broadcast their current GPS position and altitude, category of aircraft, airspeed, flight number, and whether the aircraft is turning, climbing or descending over a dedicated radio datalink. The ADS-B transmissions are received by air traffic control stations and all other ADS-B equipped aircraft within reception range. ADS-B equipped aircraft have a display unit in the cockpit picturing surrounding air traffic. Pilots and air traffic controllers will be able to "see" the positions of air traffic in the vicinity of the aircraft or ground station without the use of radar. The maximum range of the system is VHF line-of-sight, typically about 200 nautical miles (370 km).
The purpose of the system is to reduce the risk of collisions between airplanes, as well as to reduce congestion by allowing for more effective management of air traffic.
Some experts expect that ADS-B will be the next generation transponder technology. Unlike radar, ADS-B works at low altitudes and on the ground, so that it can be used to monitor traffic on the taxiways and runways of an airport. ADS-B is effective in remote areas or in mountainous terrain where there is no radar coverage, or where radar coverage is limited.
One of the greatest benefits of ADS-B is its ability to provide the same real-time information to pilots in aircraft cockpits and to ground controllers, so that for the first time, they can both "see" the same data.
The ADS-B system was developed in the 1990s. It relies on data from the Global Positioning System.
The currently (2005) used data links for ADS-B are (i) 1090 MHz (the same frequency the transponder replies to secondary surveillance radar interrogations), (ii) 978 MHz (Universal Access Transceiver), and (iii) VHF Data link mode -4 (VDL Mode 4).
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