Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through controlled airspace. The primary purpose of ATC is to prevent collisions, organise and expedite the flow of air traffic, and provide information and other support for pilots. In some countries, ATC can also provide advisory services to aircraft in non-controlled airspace. Controllers monitor the location of aircraft in their assigned airspace using radar and communicate with pilots by radio. To prevent collisions, ATC enforces traffic separation rules, which ensure each aircraft maintains a minimum amount of empty space around it. ATC services are provided to all types of aircraft, including private, military, and commercial flights. Depending on the type of flight and the class of airspace, ATC may issue mandatory instructions or non-binding advisories (known as flight information in some countries). While pilots are required to obey all ATC instructions, the pilot in command of an aircraft always retains final authority for its safe operation. In an emergency, the pilot may deviate from ATC instructions to the extent required to maintain the safety of the aircraft. Weather conditions, such as thunderstorms, strong winds, and low visibility, can significantly affect air traffic control operations, leading to delays, diversions, and the need for alternate routing.
Language According to requirements of the International Civil Aviation Organization (ICAO), ATC operations are conducted either in English, or the local language used by the station on the ground. In practice, the native language for a region is used; however, English must be used upon request.
History
In 1920, Croydon Airport near London, England, was the first airport in the world to introduce air traffic control. The 'aerodrome control tower' was a wooden hut high with windows on all four sides. It was commissioned on 25 February 1920, and provided basic traffic, weather, and location information to pilots.
In the United States, air traffic control developed three divisions. The first of several air mail radio stations (AMRS) was created in 1922, after World War I, when the U.S. Post Office began using techniques developed by the U.S. Army to direct and track the movements of reconnaissance aircraft. Over time, the AMRS morphed into flight service stations. Today's flight service stations do not issue control instructions, but provide pilots with many other flight related informational services. They do relay control instructions from ATC in areas where flight service is the only facility with radio or phone coverage. The first airport traffic control tower, regulating arrivals, departures, and surface movement of aircraft in the US at a specific airport, opened in Cleveland in 1930. Approach- and departure-control facilities were created after adoption of radar in the 1950s to monitor and control the busy airspace around larger airports. The first air route traffic control center (ARTCC), which directs the movement of aircraft between departure and destination, was opened in Newark in 1935, followed in 1936 by Chicago and Cleveland.FAA Historical Chronology, 1926–1996
After the 1956 Grand Canyon mid-air collision, killing all 128 on board, the FAA was given the air-traffic responsibility in the United States in 1958, and this was followed by other countries. In 1960, Britain, France, Germany, and the Benelux countries set up Eurocontrol, intending to merge their airspaces. The first and only attempt to pool controllers between countries is the Maastricht Upper Area Control Centre (MUAC), founded in 1972 by Eurocontrol, and covering Belgium, Luxembourg, the Netherlands, and north-western Germany. In 2001, the European Union (EU) aimed to create a 'Single European Sky', hoping to boost efficiency and gain economies of scale.
In the USSR, the first air traffic control service was organized in 1929 on the Moscow - Irkutsk air route; in 1930, control areas were defined along all existing air routes.Н. Зыков. Дирижеры воздушных трасс // журнал «Наука и жизнь», № 12, 1981. стр.58-59
Airport traffic control tower
The primary method of controlling the immediate airport environment is visual observation from the airport control tower. The tower is typically a tall, windowed structure, located within the airport grounds. The air traffic controllers, usually abbreviated 'controller', are responsible for separation and efficient movement of aircraft and vehicles operating on the taxiways and runways of the airport itself, and aircraft in the air near the airport, generally , depending on the airport procedures. A controller must carry out the job using the precise and effective application of rules and procedures; however, they need flexible adjustments according to differing circumstances, often under time pressure. In a study which compared stress in the general population and among staff working in this kind of system, there was markedly showed more stress level for controllers. This variation can be explained, at least in part, by the characteristics of the job.
Remote and virtual tower (RVT) is a system based on air traffic controllers being located somewhere other than at the local airport tower, and still able to provide air traffic control services.
Ground control
Ground control (sometimes known as , GMC) is responsible for the airport areas.
Some busier airports have surface movement radar (SMR).
Air control or local control Air control (known to pilots as or ) is responsible for the active runway surfaces.
Flight data and clearance delivery Clearance delivery is the position that issues route clearances to aircraft, typically before they commence taxiing. These clearances contain details of the route that the aircraft is expected to fly after departure.
Analogous use In the field of supply chain management, the concept of a "supply chain control tower" reflects the "end-to-end visibility" provided by an air traffic control tower.Cooke, J. A., The power of a control tower: see illustrations, CSCMP's Supply Chain Quarterly, Quarter 4, 2013, archived on 11 June 2017, accessed on 22 July 2025 Ashutoch Gupta, writing for Gartner, observes that a supply chain control tower can be established "by combining people, process, data, organization and technology to improve visibility, control and decision making".Gupta, A., What Is a Supply Chain Control Tower — And What’s Needed to Deploy One?, Gartner, published on 25 March 2022, accessed on 22 July 2025
Airports without a control tower (mandatory frequency airport) An airport with a mandatory frequency (MF), mandatory traffic advisory frequency (MTAF), mandatory broadcast zone (MBZ) or air ground communications service (AGCS) is an airport which does not have a control tower but still requires arriving and departing aircraft to communicate with other aircraft or a radio operator on a published frequency.
Mandatory frequency airports are rare in the United States, one example being Ketchikan International Airport (), but they are common in other countries such as Canada, Australia, the United Kingdom and Norway; often, an MF or MTAF airport is one with scheduled passenger service but insufficient traffic to support a control tower.
If there is a flight service specialist monitoring the frequency, the specialist will give pilots advisories about traffic, weather, and surface conditions, and may relay IFR clearances from en route controllers, but do not give clearances. In the United Kingdom, weather and traffic information can be provided by radio stations named Air Ground Communications Services (AGCS). These similarly inform pilots who are then responsible for decisions made.
Some examples of MF airports in Canada include Kingston/Norman Rogers Airport and Kuujjuaq Airport.
Approach and terminal control
In the U.S., TRACONs are additionally designated by a three-digit alphanumeric code. For example, the Chicago TRACON is designated C90.
Area control centre/en-route centre
An area control center, as opposed to a terminal control center, is a specific type of air traffic control center that primarily controls IFR traffic, or aircraft at high altitude flying by instruments, instead of aircraft that are landing or taking off. Each area control center is assigned a flight information region, and certain area control centers near the coast are also tasked with monitoring aircraft flying over the ocean. Area control centers perform similar duties to other types of air traffic control, such as rerouting aircraft to deal with adverse conditions and directing the course of aircraft to ensure separation.
Radar coverage
The position of aircraft is mainly determined by the following types of radars: En-route radar with a coverage up to 240 NM (460 km) Airport surveillance radar, with a coverage up to of 52 NM (96 km) of the airport below an elevation of 25,000 feet Surface movement radar with a coverage of the airport surface, within 2 NM (3.7 km) Secondary surveillance radar with a coverage within line-of-sight range
In order to extend their surveillance capabilities, some air navigation service providers (e.g., Airservices Australia, the U.S. Federal Aviation Administration, Nav Canada, etc.) have implemented automatic dependent surveillance – broadcast (ADS-B). This newer technology reverses the radar concept. Instead of radar 'finding' a target by interrogating the transponder, the ADS-B equipped aircraft 'broadcasts' a position report as determined by the navigation equipment on board the aircraft. ADS-C is another mode of automatic dependent surveillance, however ADS-C operates in the 'contract' mode, where the aircraft reports a position, automatically or initiated by the pilot, based on a predetermined time interval. It is also possible for controllers to request more frequent reports to more quickly establish aircraft position for specific reasons. However, since the cost for each report is charged by the ADS service providers to the company operating the aircraft, more frequent reports are not commonly requested, except in emergency situations. ADS-C is significant, because it can be used where it is not possible to locate the infrastructure for a radar system (e.g., over water). Operational display systems are now deployed and accept ADS-C inputs as part of their display.
A radar archive system (RAS) keeps an electronic record of all radar information, preserving it for a few weeks. This information can be useful for search and rescue. When an aircraft has 'disappeared' from radar screens, a controller can review the last radar returns from the aircraft to determine its likely position. For an example, see the crash report in the following citation.
Problems
Traffic
Air traffic control errors occur when the separation (either vertical or horizontal) between airborne aircraft falls below the minimum prescribed separation set (for the domestic United States) by the US Federal Aviation Administration. Separation minimums for terminal control areas (TCAs) around airports are lower than en-route standards. Errors generally occur during periods following times of intense activity, when controllers tend to relax and overlook the presence of traffic and conditions that lead to loss of minimum separation.
Weather
Congestion Constrained control capacity and growing traffic lead to flight cancellation and delays. In America, delays caused by ATC grew by 69% between 2012 and 2017. ATC staffing issues were a major factor in congestion.Estimates suggest that more efficient ATC could save 5-10% of aviation fuel by avoiding holding patterns and indirect airways.