Oceanic Air Traffic Control
Some Centers have ICAO-designated responsibility for airspace located over an ocean such as 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 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.
Read more about this topic: Area Control Center
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