Area Control Center

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This temporary flight restriction map from the Federal Aviation Administration shows the boundaries of the regions controlled by the Area Control Centers within and adjoining the continental United States, as well as the IATA airport code of each such Center operated by the United States.
This temporary flight restriction map from the Federal Aviation Administration shows the boundaries of the regions controlled by the Area Control Centers within and adjoining the continental United States, as well as the IATA airport code of each such Center operated by the United States.

In air traffic control, an Area Control Center (ACC), also known as a Center, is a facility responsible for controlling instrument flight rules aircraft en route in a particular volume of airspace (a Flight Information Region) at high altitudes between airport approaches and departures. In the United States, 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 or of another Center. Most Centers are operated by the national governments of the countries in which they are located. The general operations of Centers world-wide, and the boundaries of the airspace each Center controls, are governed by the International Civil Aviation Organization.

In some cases, the function of an Area Control Center and a TRACON are combined in a single facility such as a CERAP.

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[edit] FAA definition

The United States Federal Aviation Administration defines an ARTCC as

[a] facility established to provide air traffic control service to aircraft operating on IFR flight plans within controlled airspace, principally during the en route phase of flight. When equipment capabilities and controller workload permit, certain advisory/assistance services may be provided to VFR aircraft. An ARTCC is the U.S. equivalent of an Area Control Center (ACC).

[edit] Subdivision of airspace into sectors

The Flight Information Region controlled by a Center may be further administratively subdivided into sectors; each sector may use a distinct set of communications frequencies and personnel. An aircraft passing from one sector to another may be handed off and requested to change frequencies to contact the next sector controller. Sector boundaries are specified by an aeronautical chart.

[edit] Center operations

Controllers at work at the Washington Air Route Traffic Control Center.
Controllers at work at the Washington Air Route Traffic Control Center.

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 amplitude modulation aviation bands, 118 MHz to 137 MHz, for overland control) are published in aeronautical charts and manuals, and will also be announced to a pilot by the previous controller during a hand-off.

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, 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 to monitor the progress of flights and instruct aircraft to perform course adjustments as needed to maintain separation from other aircraft. Aircraft with which a Center has made radar contact can be readily distinguished by their transponders. Pilots may also request altitude adjustments or course changes to avoid turbulence or adverse weather conditions.

Controllers can assign routing relative to location fixes derived from latitude and longitude, or from radionavigation beacons such as VORs. See also Airway; VORs and aerial highways.

Typically, Centers have advance notice of a plane's arrival and intentions from its prefiled flight plan.

[edit] Oceanic air traffic control

Some Centers have ICAO-designated responsibility for airspace located over an ocean, the majority of which is international airspace. 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 and can supply periodic updates to a Center. See also Air traffic control: Radar Coverage.

A Center's control service for an oceanic FIR may be operationally distinct from its service for a domestic overland FIR over land, employing different communications frequencies, controllers, and a different ICAO code.

Pilots typically use high frequency radio instead of very high frequency radio to communicate with a Center when flying over the ocean, because of HF's relatively greater propagation over long distances.

[edit] ARTCCs in the United States

The continental United States has twenty centers, which are operated by the Federal Aviation Administration. The Centers are named after major cities, although most are physically located outside the cities for which they are named. Each Center is identified by a three-letter IATA airport code as well as a four-letter ICAO airport code, which is the same as the IATA code prefixed by the United States country code "K".

The United States also operates Centers outside the contiguous United States:

[edit] ACCs in Canada

Canada has seven Centers, which are operated by NAV CANADA. The ICAO code for each Canadian Center is the same as its IATA code prefixed by the Canadian country code "C".

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