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Automatic Dependent Surveillance-Broadcast

From Academic Kids

Automatic Dependent Surveillance-Broadcast (also called ADS-B) is a system by which airplanes constantly broadcast their current position and altitude, category of aircraft, airspeed, flight number, and whether the aircraft is turning, climbing or descending over a dedicated radio datalink. This functionality is known as "ADS-B out" and is the basic level of ADS-B functionality.

The ADS-B system was developed in the 1990s. It relies on data from the Global Positioning System, or any navigation system that provides an equivalent or better service. The maximum range of the system is line-of-sight, typically about 200 nautical miles (370 km).

The ADS-B transmissions are received by air traffic control stations, and potentially all other ADS-B equipped aircraft within reception range. Reception by aircraft of ADS-B data is a more advanced level of functionality and is known as ADS-B in.

The initial use of ADS-B is expected to be by air traffic control and for surveillance purposes. As such ADS-B replaces or enhances existing surveillance radars. Its lower cost (compared with conventional radar) permits high quality surveillance of air movements in airspaces where deployment of conventional radars was not cost justifiable. The outback of Australia is one such area where ADS-B will provide surveillance where previously none existed.

ADS-B works at low altitudes and on the ground, so that it can also 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.

Later on, ADS-B equipped aircraft may also have a display unit in the cockpit picturing surrounding air traffic and derived from ADS-B data (ADS-B in). Both Pilots and air traffic controllers will then be able to "see" the positions of air traffic in the vicinity of the aircraft or ground station without the use of radar, and this may be used to provide an ASAS (Airborne Separation Assistance System).

Airborne Collision Avoidance Systems may also make use of "ADS-B in", supplementing the existing TCAS collision avoidance system.

However, "ADS-B in" systems are still in the research stage and there are significant human factors and security issues to resolve before such systems ever become commonplace.

Airbus and Boeing are now expected to include ADS-B out (i.e. the transmitter of information) as standard on new-build aircraft from 2005 onwards. This is in part due to the European requirements for Mode S Enhanced Surveillance (which uses similar formats to 1090MHz Extended Squitter), and includes a requirement for ADS-B out functionality.

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 Digital link mode -4 (VDL Mode 4). 1090 MHz Extended Squitter is the globally agreed standard for ADS-B with UAT used in North America for some General Aviation aircraft (see CAPSTONE link below). VDL4 has only ever been used in trials.

Projects and Trials

ADS-B initial projects and trials first started around 1995. Standardisation activities started at a similar time and have grown in intensity since. Both areas are now seeing a significant amount of work.

It is expected that implementations of pre-operational and then operational systems will occur in future years (for example, the SEAP project South European ADS-B Project and NUP II project are both looking at pre-operational trials in 2005).

Dates of some example ADS-B projects and trials are:

  • NEAN: January 1996 December 1999
  • NEAP: September 1997 September 1998
  • NUP and NUP II: 1998 2002, followed by NUP II and soon NUP II+
  • FARAWAY: 1996 mid 1998, followed by FARAWAY II: June 1998 2000
  • Safe Flight 21/Capstone: 1999 2002, followed by Capstone II 2003 2006
  • Eurocontrol ADS Programme: 1997 - 2004
  • Eurocontrol CASCADE Programme: 2004 - present


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