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Air Traffic Service (ATS)
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A generic term meaning variously, flight information service, alerting service, air traffic advisory service, air traffic control service (area control service, approach control service or aerodrome control service).
Source: ICAO Doc 4444 PANS-ATM
Objectives of ATS
The objectives of ATS, as stated in ICAO Annex 11, are to:
- prevent collisions between aircraft;
- prevent collisions between aircraft on the manoeuvring area and obstructions on that area; note that this objective does not include the apron and ATS in general is not intended to prevent collision with terrain.
- expedite and maintain an orderly flow of air traffic;
- provide advice and information useful for the safe and efficient conduct of flights;
- notify appropriate organizations regarding aircraft in need of search and rescue aid, and assist such organizations as required.
The air traffic control (ATC) service is established to accomplish the first three objectives. While the first and third are universally applicable to all ATC units, the second one is only relevant to aerodrome control units. The fourth objective is covered by the flight information service (FIS) and the last one is subject of the alerting service.
As seen from the definition, there is a fourth type of ATS, the advisory service. No specific objectives are defined for this type of service. It is considered a temporary measure to facilitate the smoother transition from FIS to ATC.
Air traffic service is provided by specially designated air traffic service units (ATSUs). An ATSU may provide more than one type of service. For example, an air traffic control unit may provide flight information and alerting service in addition to air traffic control.
The need of service to be provided depends on a number of factors, such as:
- traffic types (commercial air transport, general aviation, etc.);
- traffic density (i.e. how busy the airspace is);
- available equipment (e.g. communication, navigation and surveillance facilities);
- meteorological conditions (e.g. hazardous phenomena typical for the particular area);
- georgraphy considerations (e.g. presence of deserts, mountains, open waters, etc.) and others.
After analysis of the factors above, Classification of Airspace is made and appropriate ATSUs are established.
The level of service to be provided depends on the airspace class and the ATS unit. An ATC unit may provide ATC service, FIS and alerting service, although FIS would normally be of lower priority. An FIS unit however will not provide ATC service. Also, if the area of responsibility of an ATC unit contains uncontrolled airspace (class G), only FIS and alerting service will be provided in this portion of airspace even though the provider is an ATC unit.
ICAO Annex 11: Air Traffic Services