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Automatic Dependent Surveillance
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Automatic Dependent Surveillance (ADS)
Automatic Dependent Surveillance (ADS) is a surveillance technique in which aircraft automatically provide, via a data link, data derived from on-board navigation and position-fixing systems, including aircraft identification, four-dimensional position and additional data as appropriate. (ICAO Doc 4444:PANS-ATM)
ADS data is displayed to the controller on a screen that resembles a radar screen
Several different forms of ADS are currently in use or under development, including:
- Automatic Dependent Surveillance-Broadcast (ADS-B) is a function on an aircraft or surface vehicle that broadcasts position, altitude, vector and other information for use by other aircraft, vehicles and by ground facilities. It has become the main application of the ADS principle.
- Automatic Dependent Surveillance-Contract (ADS-C) functions similarly to ADS-B but the data is transmitted based on a contract between a ground system and an aircraft: Demand contract, periodic contract, event contract and emergency contract. This application is most likely to find application to sparsely trafficked transcontinental or transoceanic crossings.
- Automatic Dependent Surveillance-Report (ADS-R) is a message sent by an aircraft specifying its position.
(EUROCONTROL EATM Glossary of Terms)
Automatic Dependent Surveillance-Broadcast (ADS-B)
ADS-B is covered in detail in a separate article.
Automatic Dependent Surveillance-Contract (ADS-C)
The provisions of ICAO Doc 4444: PANS-ATM, Chapter 13, apply to Contract ADS (ADS-C) only. These include the following:
- ADS ground systems used in the provision of air traffic services shall have a very high level of reliability, availability and integrity. The possibility of system failures or significant system degradations that may cause complete or partial interruptions of service shall be very remote. Back-up facilities shall be provided.
- ADS may be used in the provision of an air traffic control service, provided identification of the aircraft is unambiguously established.
- Flight data processing of ADS data may be used in the provision of an air traffic control service, provided the correlation between the ADS data downlinked by that aircraft and the flight plan details held for the aircraft has been accomplished.
- Human Factors principles shall be observed. In particular, the controller shall be provided with enough information to:
- maintain situational awareness; and,
- be capable of assuming, in the event of system malfunction, the minimum tasks for the provision of an air traffic control service, normally performed by automation.
- Information provided by the ground system may be used to perform the following functions in the provision of air traffic control services:
- enhance safety;
- maintain an accurate awareness of the air traffic situation;
- apply separation minima;
- take appropriate action regarding any significant deviation by aircraft from the terms of their respective air traffic control clearances, including their cleared routes, levels and speed where appropriate;
- provide updated position information regarding aircraft to other controllers when required; and,
- improve airspace utilisation, reduce delays, as well as provide for direct routings and more optimum flight profiles.
There are now a number of ADS-C applications but one of the earliest was Australia where ADS-C has been used to achieve air traffic surveillance outside radar coverage since 1999.
ICAO Doc 4444: PANS-ATM Chapter 13