Automatic Dependet Surveillance
Automatic Dependent Surveillance (ADS) is a surveillance technique by which an aircraft transmits, via data link, a series of parameters extracted from the on-board navigation and positioning systems.
The ADS technique provides:
- Identification of the aircraft.
- The position of the aircraft in four dimensions.
- Additional information, such as the flight plan.
The ADS has two fundamental defining characteristics: it is automatic; that is, it does not require pilot intervention to send the aircraft data to the control tower; and it is dependent because the required information is generated by the aircraft itself; that is, it depends on the on-board systems.
The ADS technique requires a navigation system and a data link in the avionics on board the aircraft and, on the ground, a station that receives the ADS information for use by the surveillance data handling systems. This new system is specially useful to complement surveillance in oceanic regions or in those in which there is little or no radar coverage. It also improves surveillance in areas currently covered by radar (thanks to air-to-air surveillance or the collection of additional on-board data, such as flight plans, to be used by the surveillance systems).
ADS-B and ADS-C
ADS has been broken down into two techniques that are based on the same principles: ADS-B (Broadcast) and ADS-C (Contract).
- ADS-B: consists in broadcasting, via data links, certain on-board parameters at frequent, regular intervals. It is characterised by:
- The data collected by ADS-B are sent and broadcast periodically by the aircraft.
- The primary characteristic of ADS-B is that it facilitates air-to-ground data transmission, as well as air-to-air.
- Air-to-air data transmission provides an on-screen representation of nearby traffic in the aircraft, CDTI (Cockpit Display of Traffic Information).
- There are mainly three technologies that can be used to implement ADS-B: S-Mode Extended Squitter, VDL Mode 4 and UAT.
- ADS-C: involves transmitting certain data between the aircraft and a ground station. Its primary characteristics include:
- Data is transmitted only when a contract has been established with a particular ground station; several independent contracts may be maintained with several different ground stations.
- The ground station determines the frequency of the transmissions and their parameters.
- There are four types of contracts: periodical, on-demand, by event and emergency.
- There are two basic technologies used by ADS-C: FANS-1/A, based on the ACARS data link, and the ADS-C ATN system.
CPDLC (Controller to Pilot Data Link Communications)
Air traffic control system security relies on reliable, precise communications between controllers and pilots. Currently, these are voice communications established through the ground stations and special on-board equipment in the aircraft. In recent years, new systems have been developed to facilitate digital message communications between controllers and pilots. These communications are called CPDLC (Controller to Pilot Data Link Communications) and are already used in some parts of the world, including the Canary Islands.
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