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Air Traffic Control (ATC) is a service of ground-based controllers that directs and coordinates aircraft to improve safety and efficiency.

Air Traffic Control (ATC) refers to a service provided by ground-based controllers who direct and coordinate air traffic in order to improve safety and efficiency. The full ICAO term is Air Traffic Control Service.

ATC is usually provided at a national level by a civilian or military organization (depending on the country) although in some regions there may also be an international ATC organization, such as Eurocontrol in Europe. Depending on local regulations, ATC may provide services to all flights at all times, or to only some flights at certain times or in certain airspace.

ATC services vary by country and location, but they typically include:

  • Ground control, which directs aircraft moving on the ground at an airport
  • Tower control, which directs aircraft on final approach to or taking off from an airport
  • Arrival/Departure control, which directs aircraft arriving in or departing from an airport's local airspace
  • En route control, which directs aircraft as they cruise between airports

Controllers use radar and other technologies to plan, track and direct air traffic. They communicate instructions to pilots verbally by radio, or - if possible - by light gun in case of radio failure.

If a flight is under ATC control, controllers may provide different types of instructions to pilots, by radio. They may instruct the pilot to fly a specific altitude, heading or speed; clear (authorize) pilots to take off, land or start an instrument approach; or provide other instructions as required. The main purpose of ATC instructions is to avoid collisions by providing adequate separation between aircraft; a secondary, but still important purpose is to improve efficiency by routing flights so as to avoid unnecessary delays.

Pilots are usually required to follow all ATC instructions unless there is a critical safety reason not to, but pilots may request ATC to allow an alternative flight path and the pilot always has final authority over the flight. In an emergency, ATC can assist pilots by providing guidance to the nearest airport, directing other air traffic away from the aircraft in distress, giving information about weather conditions and so on.

This tag is appropriate for all questions about ATC organizations, procedures and interactions between ATC and pilots.