Air traffic control

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Air traffic control tower (tower) at Amsterdam Airport Schiphol , Netherlands

Air traffic control ( FVK ; English air traffic control , ATC ) is a sub-area of air traffic control and describes the ground-based service of air traffic controllers who manage aircraft on the ground and in the air. The primary purpose of air traffic control is staggering to avoid aircraft to collisions, organizing and accelerating the flow of traffic, and the provision of information and support of the pilots. In some states, air traffic control also partially performs security and defense functions (as in the United States ) or is carried out entirely by the military (as in Brazil ).

The avoidance of collisions is achieved by staggering. The main focus here is on maintaining the minimum vertical and horizontal distances between the aircraft. Many aircraft now have a collision warning system , which exists as an additional aid in addition to the primary air traffic control. In addition to its main task, air traffic control offers other services such as information for pilots, weather data, navigation information and NOTAM .

In many countries, air traffic control is carried out in a large part of the airspace and is available to all airspace users (private, commercial and military). When air traffic controllers are responsible for the separation of all or some aircraft , this airspace is referred to as controlled airspace . Depending on the airspace class and the type of flight, air traffic control will give instructions to be followed by the pilot, or just information to help the pilot. In all cases, however, the ultimate responsibility for the safe conduct of the flight lies with the pilot in command , who may deviate from the instructions of air traffic control in an emergency.

History in Germany

The Aviation Warning Service was established in 1910 to provide aircraft pilots with meteorological and bearing information by telegram . The radio stations were mainly located at the airports.

From 1945, the entire airspace control was subject to the air traffic control services of the victorious powers. In 1953 the Federal Agency for Air Traffic Control (BFS) was founded in Frankfurt am Main and was responsible for civil air traffic control. In 1959 the Federal Ministry of Transport and the Federal Ministry of Defense formally established the division of civil-military tasks.

The controls in the airspace of the GDR were carried out by Interflug or by the main department XIX (transport) of the Ministry for State Security (MfS).

The Allies controlled the air corridor to Berlin until October 3, 1990 .

The air traffic control centers are divided into "ACC" (Area Control Center) and "UAC" (Upper Area Control Center) according to the respective area of ​​responsibility. The tasks of an ACC are located in the lower area of ​​the airspace in the height band from the ground to about 8 km.

History in the USA

Contrails from aircraft arriving and departing at London Heathrow Airport . Crossing flight paths are closely monitored to prevent collisions.

In 1919 the International Commission for Air Navigation (ICAN) was created to develop general rules for air traffic. Their rules and procedures were applied in most of the states in which airplanes operated. The United States did not join the ICAN Convention, but developed its own air traffic rules from 1926. The first simple regulations were made, for example the instruction to pilots not to take off until there was no longer any risk of a collision with other aircraft landing or just taking off. As the number of traffic increased, it became clear that such general rules were insufficient to avoid collisions. Airport operators began to set up some kind of air traffic control based on visual signals. Early “air traffic controllers” stood on the airfield and used various flags to communicate with the pilots.

With the increasing number of radio equipment in aircraft, radio-controlled control towers replaced the flag signals. In 1930, the first radio control tower began operating in the United States at Cleveland Municipal Airport. By 1935, about 20 control towers operated with radio.

A further increase in traffic resulted in the need for air traffic control that is also responsible outside the airfields. In 1935, the airlines that made the most use of Chicago, Cleveland and Newark airfields agreed to coordinate air traffic between these cities. In December, the first air traffic control center opened in Newark, New Jersey. Further centers in Chicago and Cleveland followed in 1936.

The first air traffic controllers tracked the position of the aircraft using markings on maps and flight plan data on boards. They had no direct radio contact with the aircraft, but were in telephone contact with the operational planners of the airlines and the airfield controllers.

In July 1936, air traffic control in the United States became a federal responsibility and the first budget item was $ 175,000 (now $ 2,665,960). The government provided air traffic control on the airways, but local authorities remained responsible for the operation of the control towers. By 1944 there were 115 control towers in the United States. After the Second World War, air traffic control at many airfields was permanently the responsibility of the federal government. At the same time, the Civil Aeronautics Administration (CAA) expanded the air traffic control route system.

With the introduction of radar , a revolutionary development began in the mid-1940s. For the first time, air traffic controllers were able to see and track the current position of aircraft on display devices. The first experimental radar-based civil control tower began operating in 1946. In 1952 the CAA started the routine use of radar for approach and departure control. Four years later, an order was placed for the procurement of long-range radar devices for route control.

In 1960 the Federal Aviation Administration (FAA), which succeeded the CAA in 1958, began successfully testing secondary radar systems and on-board transponders in certain airspaces . These helped to determine the position of aircraft and improve the radar display. In addition, pilots in these airspaces only had to fly by instruments - regardless of the weather - and stay in contact with the air traffic controllers. Under these conditions, the air traffic controllers were able to halve the separation between the aircraft.

From 1965 to 1975, the FAA developed complex computer systems that automated and improved the display and analysis of radar data, thereby enabling air traffic controllers to concentrate more on managing air traffic.

In April 1970, a Central Flow Control Facility was set up to reduce delays in air traffic by avoiding occasional overloading of the air traffic control points.

With the introduction of the National Airspace System (NAS) in January 1982, a comprehensive modernization of the air traffic control points and communication and monitoring systems took place.

Another stage of modernization began in 1999 when the standard Terminal Automation Replacement System with new display devices and more efficient workstations was introduced.

Current developments aim to improve communication, navigation and surveillance, and mainly use the advanced transponders, the global positioning system and more precise radars. At the same time, the improvement of the cockpit displays should provide pilots with more and more accurate information about other traffic, weather and possible dangers.


In accordance with the requirements of the International Civil Aviation Organization (ICAO), air traffic control services are conducted in either the English language or the language used by the ground station. In practice, the local language is often used, but the English language must be used upon request.

Airport control

Interior view of the tower at Sao Paulo-Guarulhos Airport , one of the busiest airports in Latin America

The primary method of monitoring the immediate vicinity of the airport is by visual observation from the control tower . Tower controllers are responsible for the separation and efficient traffic management of aircraft and vehicles that operate on the taxiways and runways as well as in the air in the immediate vicinity of the airfield ( control zones , usually within a radius of 2 to 5 nautical miles , or 3, 7 to 9.2 kilometers).

Radar displays are also available for the controllers at some airports. The controllers can use secondary radar to display incoming and outgoing traffic on a digital map with information about callsign , speed, direction of flight and altitude .

The areas of responsibility of the controllers at the airport can basically be divided into three categories: field control, ground control and clearance delivery. Other services such as apron control and marshalling are available depending on the volume of traffic at the airport, but are not provided by air traffic control, but by the airport operator. Different local procedures are regulated in each control tower; the following sections provide an overview of the basic division of tasks in the tower.

Roll control

The taxiing control (English ground control ) is responsible for the runway of the airfield and other operating areas. This usually includes taxiways, disused runways and some waiting areas. Exact delimitations of the area of ​​responsibility are clearly laid down in local regulations. Every aircraft, every other vehicle and every working or passing person has to obtain clearance from taxiing control within this area. Usually this is done over a radio link, but there are different procedures. Most aircraft and vehicles are equipped with radios. If a radio connection is not possible, they have to establish contact by light signal or must be accompanied by vehicles equipped with radio. Portable radios or cell phones are usually available for people. The taxiing control is essential for smooth operations at the airport, as the sequence of the departures and the threading of the arriving aircraft must be harmonized.

At larger airfields, a ground radar is often available for roll control, which shows the current position of the aircraft on the ground. In this way, dangers can be avoided and rapid operation can be maintained, especially at night and when visibility is poor.

Place control

The area control, called tower (English tower ), is responsible for the active runways and the traffic in the control zone. The area control issues clearances for take-off and landing on the condition that specified minimum distances are observed. In unsafe situations, approaching aircraft can be instructed to take off and be re-queued for the approach.

Within the control tower, close coordination between taxi control and site control is necessary. Taxi control must obtain authorization if they want to cross an active runway with aircraft or vehicles. On the other hand, the area control must ensure that the taxi control is informed of any operations that could affect the operation on the taxiways. Furthermore, she has to coordinate with the pilots of the approach control in order to use gaps in the approaching traffic for starting aircraft or for crossing traffic. Crew Resource Management (CRM) training is used intensively to make these communication processes more efficient and secure.

Approval / flight data

The release (English clearance delivery ) is the position transmitted route which enables on the aircraft, usually before they start with the rolling operation. The route releases contain details of the route the aircraft should fly after take-off. The approval is coordinated with the supra-local district control offices . The release procedures are often automated or generally regulated in local agreements. If weather conditions or high traffic density for an airport or a certain airspace become critical, it may be necessary to guide the aircraft over other routes or to have them wait on the ground and move their slot to avoid overloading. The main purpose of clearance is to ensure that all aircraft are receiving the correct route and slot time. In cooperation with taxi control, it must be ensured that the aircraft reach the runway at the required time and are ready for departure. The release is at some airports for permission to pushback responsible and engine start, to avoid congestion on taxiways and apron.

Flight data is a task that is also routinely taken over by the release . Both air traffic controllers and pilots are constantly supplied with the latest information: weather changes, system failures, delays on the ground, closings of runways etc. Flight Data also informs pilots by means of an endless loop broadcast on a separate frequency, known as the Automatic Terminal Information Service ( ATIS).

Approach control

Many airfields have a radar control post that is assigned to the airfield. In most countries it is called Terminal Control , in the USA it is called TRACON (Terminal Radar Approach Control). Although conditions differ at each aerodrome, the controllers usually handle traffic within 30 to 50 nautical miles (56 to 93 kilometers) of the aerodrome. If several busy airports are close together, an approach control point takes over the services for all airports. The boundaries of the airspace of approach control vary greatly depending on the local traffic flow, neighboring airports and the nature of the terrain. A large and complex example of this was the London Terminal Control Center , which controlled traffic for five London airports up to 20,000 feet high and 100 nautical miles away.

Approach controllers are responsible for providing all air traffic control services in their airspace. The traffic flow can be roughly divided into departures, approaches and overflights. When aircraft enter and leave the approach control airspace, they are handed over to the next responsible control point (e.g. tower, district control point or adjacent approach control points). Approach control is responsible for maintaining specified flight altitudes when handing over to adjacent locations and for ensuring that aircraft approach the landing at a suitable rate.

Not all airports have an approach control point. In this case, the district control point or a neighboring approach control point takes over the traffic and coordinates it directly with the tower. At some of these airfields, the tower can offer an approach procedure without radar support if the aircraft cannot land in sight.

Track control

The training department at the Washington Air Route Traffic Control Center, Washington, DC , United States

Air traffic control is also available to aircraft between airports through the Area Control Center (ACC). Pilots either fly according to Visual Flight Rules (VFR) or Instrument Flight Rules (IFR). Air traffic controllers are responsible for the aircraft in different ways depending on the flight rules. While IFR traffic is under positive control, VFR traffic can receive traffic information and navigation instructions as far as air traffic control capacity permits.

The route control controllers issue clearances and instructions for aircraft in the air, and pilots must follow these instructions. The controllers also provide air traffic control services to smaller airports by issuing clearances for arrivals and departures. They observe a number of specified minimum separation distances for aircraft, which can vary depending on the equipment and the procedures used.


Air traffic controllers for route control work in ACCs (Area Control Centers) , which are usually only referred to as centers. In the United States there is also the designation ARTCC (Air Route Traffic Control Center) . Each center is responsible for thousands of square miles of airspace (known as the Flight Information Region ) and the airfields within it. Centers manage IFR flights from the time they take off or leave the approach sector until they arrive at another airport or approach sector. Centers can also accept VFR flights that are already en route and add them to IFR traffic. However, these flights must comply with the VFR rules until they are cleared by Center.

Center controllers are responsible for raising aircraft to their requested altitude while at the same time ensuring that the separation to other aircraft is maintained. In addition, the aircraft must be integrated into the traffic flow according to their route. These endeavors are complicated by intersecting traffic, bad weather, and traffic density. When an aircraft approaches its destination, the centers are responsible for complying with restrictions on flight altitude above fixed approach points and for having staggered the approaches so that there are no bottlenecks. This traffic flow management already starts during the long-haul flight, as the controllers position aircraft with the same destination so that they do not arrive at the same time.

As soon as an aircraft reaches the limit of the airspace of one center, it is handed over to the next center. In some cases, the details of the flight are exchanged between the air traffic controllers in order to enable a smooth takeover, in other cases no separate coordination is necessary due to compliance with the agreed handover criteria. With the handover, the aircraft will be assigned a new frequency and will contact the new sector. This process is repeated until the aircraft has reached the approach sector of its destination airport.

Radar coverage

Since centers control a large airspace, they mostly use long-range radars that have the ability to detect aircraft at higher altitudes up to 200 nautical miles (370 kilometers) away. You can also use the approach control radars if they provide a better "picture" or if they depict part of the airspace that is not covered by long-range radar.

In the United States, at higher altitudes, there is 90% radar coverage of the airspace, often by multiple radar systems. Nevertheless, there can be gaps at lower altitudes due to high terrain or great distances to the next radar station. A center may need several radar devices in order to be able to monitor the airspace allocated to it, or it may even have to rely on position information from the pilots. In order to prepare the abundance of available data for the controller, automated systems are available that generate a single clear image from all radar data and display the data in a clear format.

The centers also monitor air traffic over the oceans, since these areas with the North Atlantic Tracks are also part of a flight information region . There are no radar devices available for the oceans, so the air traffic controllers and pilots only follow established flight procedures. These procedures use aircraft position reports, time, altitude, distance and speed to ensure separation. Pilots record the available information on control strips and in computer systems specially developed for ocean areas. When using this method, aircraft must be staggered at a greater distance, which reduces the overall capacity of the individual routes.

Some air traffic control (such as Airservices Australia , The Federal Aviation Administration , NAVCANADA etc.) have introduced ADS-B (Automatic Dependent Surveillance - Broadcast) as part of their surveillance capabilities. This new technology reverses the concept of radar. Instead of a radar that has to find and recognize a target, ADS-equipped aircraft independently transmit position reports determined using their own navigation instruments. ADS-B is important because it can be used where radars are not available. With the development of computerized radar displays, ADS-B information can be displayed on them. This technology is currently in use over the North Atlantic and Pacific, where several states share responsibility for control of the airspace.



The day-to-day problems air traffic control faces are mainly based on the volume of air traffic and the weather. Various factors determine the number of landings at an airport in a given period of time. Each landing plane must touch down, slow down and leave the runway before the next plane crosses the beginning of the runway. This process takes at least one to four minutes per aircraft. If there are departures between approaches, a runway can accommodate around 30 approaches per hour. A large airport with two runways for approaches can thus process around 60 approaches in good weather. Problems arise when airlines want to make more approaches to an airport than it can physically handle or when delays lead to groups of aircraft arriving at the same time that were originally supposed to arrive with a delay. Aircraft then have to hold a holding pattern in the air above a specified point until they can be safely threaded into the approach. Until the 1990s, holding patterns, which have a significant impact on the environment and costs, were regularly encountered at many airports. Advances in computer technology now allow air traffic flow management to sort aircraft hours in advance. This means that departures can be delayed before take-off (by allocating a new slot ) or the speed in flight can be adjusted in order to considerably shorten the times in the holding patterns.


In addition to the capacity limits of the runways, the flight weather is an essential factor for air traffic. Rain, ice or snow on the runway can mean that landing aircraft take longer to slow down and leave the runway and thus the time between two approaches has to be increased. Fog also leads to a reduction in approach rates. On the other hand, this results in an increase in delays in the air. If more approaches are planned than can be safely recorded, the weather at the destination airport can also lead to delays in departure.

Thunderstorms are a major problem for the centers as they pose a number of dangers for aviation. Aircraft are diverted around the thunderstorms, which can lead to a reduction in the capacity of the route network through greater staggering or to an overload of a single route between the thunderstorms. Occasionally, thunderstorms lead to a delay in departures if routes or places have been closed due to thunderstorms. Similar problems arise in the event of heavy and / or long-lasting snowfalls, which make runway closures necessary during clearing. Approaching traffic must then u. U. be staggered by holding company .

A lot of money has been invested in the development of software to make these processes efficient. Nevertheless, in some centers, air traffic controllers still write data on paper control strips for each flight and personally coordinate flight paths. In newer systems, these control strips have been replaced by electronic screen displays and older systems are gradually being modernized.


A necessity for the reliable differentiation of air traffic participants is the allocation and use of call signs . By default, the callsign for flights is the respective aircraft registration number of the aircraft, such as "N12345" or "C-GABC". These markings are usually painted on the tail of the aircraft, but can also be on the engines, on the fuselage, or often on the wings.

For airlines , their own call signs are permanently assigned by the ICAO (and by the air force for military flights). These are written callsigns made up of a combination of three letters such as KLM, AAL, SWA, BAW, DLH, followed by the flight number such as AAL872, BAW018. In this way, they are shown in flight plans and as labels on radar displays. There are also radio call signs that are used in contact between the controller and the pilot. They are not always the same as the written callsigns. For example, BAW stands for British Airways , but the word Speedbird is used in radio communications .

The part of the flight number is determined by the operator of the aircraft. This way the same callsign can be used for the same flight every day, even if the departure time may vary from day to day. The call sign for the return flight often only differs from the outbound flight in the last digit. In general, flight numbers are even for eastbound flights and odd for westbound flights. In order to reduce the possibility of confusing two similar call signs, European airlines in particular have switched to using alphanumeric call signs. For example DLH23LG, spoken as Lufthansa -two-tree-lima-golf. In addition, an air traffic controller has the right to change the callsign of the flight within his or her sector to avoid confusion, usually by using the aircraft identification alternatively.

Before 1980, IATA and ICAO used the same two-letter callsign. With the advent of numerous new airlines, ICAO introduced the three letter callsigns mentioned above. The IATA callsigns are currently still used on display boards in airports, but no longer in air traffic control. As an example, AA is the IATA callsign for American Airlines and the ICAO callsign is AAL. Further examples are LY / ELY for El Al , DL / DAL for Delta Air Lines and LH / DLH for Lufthansa.

See also


Web links

Commons : Air traffic control  - collection of pictures, videos and audio files

Individual evidence

  1. FAA 7110.65 2-1-1 . Archived from the original on June 7, 2010. Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved December 29, 2010. @1@ 2Template: Webachiv / IABot /
  2. a b IDAO FAQ . Retrieved March 3, 2009.