air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airsp ...

, an area control center (ACC), also known as a center or en-route center, is a facility responsible for controlling aircraft flying in the

airspace Airspace is the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere. It is not the same as aerospace, which is th ...

of a given

flight information region In aviation, a flight information region (FIR) is a specified region of airspace in which a flight information service and an alerting service (ALRS) are provided. The International Civil Aviation Organization (ICAO) delegates which country is re ...

(FIR) at high altitudes between airport approaches and departures. In the US, such a center is referred to as an air route traffic control center (ARTCC). A center typically accepts traffic from — and ultimately passes traffic to — the control of a

terminal control center Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airsp ...

or another center. Most centers are operated by the national governments of the countries in which they are located. The general operations of centers worldwide, and the boundaries of the airspace each center controls, are governed by the

International Civil Aviation Organization The International Civil Aviation Organization (ICAO, ) is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation, and fosters the planning and development of international a ...

(ICAO). In some cases, the function of an area control center and a terminal control center are combined in a single facility. For example, NATS combines the

London Terminal Control Centre The London Terminal Control Centre (LTCC) was an air traffic control centre based in West Drayton, in the London Borough of Hillingdon, England, approximately north of London Heathrow Airport. Operated by National Air Traffic Services (NATS) ...

(LTCC) and London Area Control Centre (LACC) in

Swanwick, Hampshire Swanwick () is a village in Hampshire, England, east of the River Hamble and north of the M27 motorway. The village is located within the borough of Fareham and is the site of the London Area Control Centre (LACC) and the London Terminal Contr ...

FAA definition

The United States

Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic ...

(FAA) defines an ARTCC as: An ARTCC is the U.S. equivalent of an area control center (ACC). There are 22 ARTCCs located in nineteen states.

Subdivision of airspace into sectors

The flight information region controlled by a center may be further administratively subdivided into areas comprising two to nine sectors. Each area is staffed by a set of controllers trained on all the sectors in that area. Sectors use distinct radio frequencies for communication with aircraft. Each sector also has secure landline communications with adjacent sectors, approach controls, areas, ARTCCs, flight service centers, and military aviation control facilities. These landline communications are shared among all sectors that need them and are available on a first-come, first-served basis. Aircraft passing from one sector to another are handed off and requested to change frequencies to contact the next sector controller. Sector boundaries are specified by an

aeronautical chart An aeronautical chart is a map designed to assist in the navigation of aircraft, much as nautical charts do for watercraft, or a roadmap does for drivers. Using these charts and other tools, pilots are able to determine their position, safe alt ...

Center operations

Air traffic controllers working within a center communicate via radio with pilots of instrument flight rules aircraft passing through the center's airspace. A center's communication frequencies (typically in the

very high frequency Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VH ...

aviation bands, using amplitude modulation (AM) 118 MHz to 137 MHz, for overland control) are published in aeronautical charts and manuals, and are also announced to a pilot by the previous controller during a hand-off. Most VHF radio assignments also have a UHF (225 to 380 MHz) paired frequency used for military flights. In addition to radios to communicate with aircraft, center controllers have access to communication links with other centers and TRACONs. In the United States, centers are electronically linked through the

National Airspace System The National Airspace System (NAS) is the airspace, navigation facilities and airports of the United States along with their associated information, services, rules, regulations, policies, procedures, personnel and equipment. It includes components ...

, which allows nationwide coordination of traffic flow to manage congestion. Centers in the United States also have electronic access to nationwide radar data. Controllers use

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...

to monitor the progress of flights and instruct aircraft to perform course adjustments as needed to maintain separation from other aircraft. Aircraft with center contact can be readily distinguished by their

transponders In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''. In air navigation or radio frequency identification, a flight tra ...

. Pilots may request altitude adjustments or course changes for reasons including avoidance of

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...

or adverse weather conditions. Controllers can assign routing relative to location fixes derived from

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...

and

longitude Longitude (, ) is a geographic coordinate that specifies the east– west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek let ...

, or from radionavigation beacons such as VORs. Typically, centers have advance notice of a plane's arrival and intentions from its pre-filed

flight plan Flight plans are documents filed by a pilot or flight dispatcher with the local Air Navigation Service Provider (e.g. the FAA in the United States) prior to departure which indicate the plane's planned route or flight path. Flight plan forma ...

Oceanic air traffic control

Some centers have ICAO-designated responsibility for airspace located over an ocean such as ZNY and ZOA, the majority of which is

international airspace Airspace is the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere. It is not the same as aerospace, which is the ...

. Because substantial volumes of oceanic airspace lie beyond the range of ground-based radars, oceanic airspace controllers have to estimate the position of an airplane from pilot reports and computer models ( procedural control), rather than observing the position directly ( radar control, also known as positive control). Pilots flying over an ocean can determine their own positions accurately using the

Global Positioning System The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite ...

and can supply periodic updates to a center. A center's control service for an oceanic

may be operationally distinct from its service for one over land, employing different communications frequencies, controllers, and a different ICAO code. Pilots typically use

high frequency High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten ...

radio instead of very high frequency radio to communicate with a center when flying over the ocean, because of HF's relatively greater

propagation Propagation can refer to: *Chain propagation in a chemical reaction mechanism *Crack propagation, the growth of a crack during the fracture of materials * Propaganda, non-objective information used to further an agenda * Reproduction, and other for ...

over long distances. Military aircraft, however, are typically installed with ARC-231 SATCOMs that allow over-the-horizon communication.

List of area control centers

Area control centers (ACCs) control IFR air traffic in their

(FIR). The current list of FIRs and ACCs is maintained by the

(ICAO).List of current FIRs from the ICAO. Note that the map gives the shapefile coordinates for each FIR, and the page source gives a list of current ACCs in text form
Note that the cited ICAO source gives the shapefile coordinates for each FIR, and also its page source gives a list of current ACCs in text form. The following is the alphabetic list of all ACCs and their FIRs :

References