Area control center

The United States Federal Aviation Administration (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. ==Center operations==

, United States Air traffic controllers working within a center communicate via radio with pilots of instrument flight rules (IFR) aircraft passing through the center's airspace. A center's communication frequencies (typically in the very high frequency 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, 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 operational display systems to visualize radar signals, 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. Pilots may request altitude adjustments or course changes for reasons including avoidance of 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. Typically, centers have advance notice of a plane's arrival and intentions from its pre-filed flight plan. ==Oceanic air traffic control==

. This map depicts overflight fee regions. The yellow regions are where the U.S. provides enroute ATC services (mostly over land territory). The blue regions are where the U.S. provides oceanic ATC services over international waters. Some centers have ICAO-designated responsibility for airspace located over an ocean such as ZNY and ZOA, 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 or other means, and can supply periodic updates to a center. A center's control service for an oceanic flight information region 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 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. Military aircraft, however, are typically equipped with ARC-231 SATCOMs that allow over-the-horizon communication. ==See also==