Air traffic control
Overview
 
Air traffic control is a service provided by ground-based controllers
Air traffic controller
Air traffic controllers are the people who expedite and maintain a safe and orderly flow of air traffic in the global air traffic control system. The position of the air traffic controller is one that requires highly specialized skills...

 who direct aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots when able. In some countries, ATC may also play a security or defense role (as in the United States), or be run entirely by the military (as in Brazil).

Preventing collisions is referred to as separation
Separation (air traffic control)
In air traffic control, separation is the name for the concept of keeping an aircraft outside a minimum distance from another aircraft to reduce the risk of those aircraft colliding, as well as prevent accidents due to wake turbulence....

, which is a term used to prevent aircraft from coming too close to each other by use of lateral, vertical and longitudinal separation minima; many aircraft now have collision avoidance systems installed to act as a backup to ATC observation and instructions.
Encyclopedia
Air traffic control is a service provided by ground-based controllers
Air traffic controller
Air traffic controllers are the people who expedite and maintain a safe and orderly flow of air traffic in the global air traffic control system. The position of the air traffic controller is one that requires highly specialized skills...

 who direct aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots when able. In some countries, ATC may also play a security or defense role (as in the United States), or be run entirely by the military (as in Brazil).

Preventing collisions is referred to as separation
Separation (air traffic control)
In air traffic control, separation is the name for the concept of keeping an aircraft outside a minimum distance from another aircraft to reduce the risk of those aircraft colliding, as well as prevent accidents due to wake turbulence....

, which is a term used to prevent aircraft from coming too close to each other by use of lateral, vertical and longitudinal separation minima; many aircraft now have collision avoidance systems installed to act as a backup to ATC observation and instructions. In addition to its primary function, the ATC can provide additional services such as providing information to pilots, weather and navigation information and NOTAM
NOTAM
NOTAM or NoTAM is the quasi-acronym for a "Notice To Airmen". NOTAMs are created and transmitted by government agencies and airport operators under guidelines specified by Annex 15: Aeronautical Information Services of the Convention on International Civil Aviation...

s (NOtices To AirMen).

In many countries, ATC services are provided throughout the majority of airspace, and its services are available to all users (private, military, and commercial). When controllers are responsible for separating some or all aircraft, such airspace is called "controlled airspace
Controlled airspace
Controlled airspace is an aviation term used to describe airspace in which ATChas the authority to control air traffic, the level of which varies with the different classes of airspace. Controlled airspace is established mainly for three different reasons:...

" in contrast to "uncontrolled airspace
Uncontrolled airspace
Uncontrolled airspace is airspace where an Air Traffic Control service is not deemed necessary or cannot be provided for practical reasons. According to the airspace classes set by ICAO both class F and class G airspace are uncontrolled...

" where aircraft may fly without the use of the air traffic control system. Depending on the type of flight and the class of airspace, ATC may issue instructions that pilots
Aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...

 are required to follow, or merely flight information (in some countries known as advisories) to assist pilots operating in the airspace. In all cases, however, the pilot in command has final responsibility for the safety of the flight, and may deviate from ATC instructions in an emergency.

Language

Pursuant to requirements of the International Civil Aviation Organization (ICAO)
International Civil Aviation Organization
The International Civil Aviation Organization , pronounced , , is a specialized agency of the United Nations. It codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth...

, ATC operations are conducted either in the English language
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

 or the language used by the station on the ground. In practice, the native language for a region is normally used, however the English language
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

 must be used upon request.

Airport control

The primary method of controlling the immediate airport environment is visual observation from the airport traffic control tower (ATCT)
Control tower
A control tower, or more specifically an Air Traffic Control Tower , is the name of the airport building from which the air traffic control unit controls the movement of aircraft on and around the airport. Control towers are also used to control the traffic for other forms of transportation such...

. The ATCT is a tall, windowed structure located on the airport grounds. Aerodrome or Tower controllers are responsible for the 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 5 to 10 nautical miles (9 to 18 km) depending on the airport procedures.

Radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

 displays are also available to controllers at some airports. Controllers may use a radar system called Secondary Surveillance Radar
Secondary surveillance radar
Secondary surveillance radar is a radar system used in air traffic control , that not only detects and measures the position of aircraft i.e. range and bearing, but also requests additional information from the aircraft itself such as its identity and altitude...

 for airborne traffic approaching and departing. These displays include a map of the area, the position of various aircraft, and data tags that include aircraft identification, speed, heading, and other information described in local procedures.

The areas of responsibility for ATCT controllers fall into three general operational disciplines; Local Control or Air Control, Ground Control, and Flight Data/Clearance Delivery—other categories, such as Apron
Airport ramp
The airport ramp or apron is part of an airport. It is usually the area where aircraft are parked, unloaded or loaded, refueled or boarded. Although the use of the apron is covered by regulations, such as lighting on vehicles, it is typically more accessible to users than the runway or taxiway...

 Control or Ground Movement Planner, may exist at extremely busy airports. While each ATCT may have unique airport-specific procedures, such as multiple teams of controllers ('crews') at major or complex airports with multiple runways, the following provides a general concept of the delegation of responsibilities within the ATCT environment.

Remote and Virtual Tower
Remote and Virtual Tower
Remote and Virtual Tower is a new concept where the Air Traffic Service at an airport is performed somewhere else than in the local control tower.-Concept:...

 (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. Displays for the Air Traffic Controllers may be either optical live video and/or synthetic images based on surveillance sensor data.

Ground control

Ground Control (sometimes known as Ground Movement Control abbreviated to GMC or Surface Movement Control abbreviated to SMC) is responsible for the airport "movement" areas, as well as areas not released to the airlines or other users. This generally includes all taxiways, inactive runways, holding areas, and some transitional aprons or intersections where aircraft arrive, having vacated the runway or departure gate. Exact areas and control responsibilities are clearly defined in local documents and agreements at each airport. Any aircraft, vehicle, or person walking or working in these areas is required to have clearance from Ground Control. This is normally done via VHF/UHF radio, but there may be special cases where other processes are used. Most aircraft and airside vehicles have radios. Aircraft or vehicles without radios must respond to ATC instructions via aviation light signals
Aviation light signals
In the case of a radio failure or aircraft not equipped with a radio, air traffic control may use a signal lamp to direct the aircraft. The signal lamp has a focused bright beam and is capable of emitting three different colors: red, white and green. These colors may be flashed or steady, and have...

 or else be led by vehicles with radios. People working on the airport surface normally have a communications link through which they can communicate with Ground Control, commonly either by handheld radio or even cell phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...

. Ground Control is vital to the smooth operation of the airport, because this position impacts the sequencing of departure aircraft, affecting the safety and efficiency of the airport's operation.

Some busier airports have Surface Movement Radar (SMR), such as, ASDE-3, AMASS or ASDE-X
ASDE-X
Airport Surface Detection Equipment, Model X, or ASDE-X, is a runway-safety tool that enables air traffic controllers to detect potential runway conflicts by providing detailed coverage of movement on runways and taxiways...

, designed to display aircraft and vehicles on the ground. These are used by Ground Control as an additional tool to control ground traffic, particularly at night or in poor visibility. There are a wide range of capabilities on these systems as they are being modernized. Older systems will display a map of the airport and the target. Newer systems include the capability to display higher quality mapping, radar target, data blocks, and safety alerts, and to interface with other systems such as digital flight strips.

Local control or air control

Local Control (known to pilots as "Tower" or "Tower Control") is responsible for the active runway surfaces. Local Control clears aircraft for takeoff or landing, ensuring that prescribed runway separation will exist at all times. If Local Control detects any unsafe condition, a landing aircraft may be told to "go-around
Go-around
A go-around is an aborted landing of an aircraft that is on final approach.- Origin of the term :The term arises from the traditional use of traffic patterns at airfields. A landing aircraft will first join the circuit pattern and prepare for landing in an orderly fashion...

" and be re-sequenced into the landing pattern by the approach or terminal area controller.

Within the ATCT, a highly disciplined communications process between Local Control and Ground Control is an absolute necessity. Ground Control must request and gain approval from Local Control to cross any active runway with any aircraft or vehicle. Likewise, Local Control must ensure that Ground Control is aware of any operations that will impact the taxiways, and work with the approach radar controllers to create "holes" or "gaps" in the arrival traffic to allow taxiing traffic to cross runways and to allow departing aircraft to take off. Crew Resource Management
Crew Resource Management
Crew resource management or Cockpit resource management is a procedure and training system in systems where human error can have devastating effects. Used primarily for improving air safety, CRM focuses on interpersonal communication, leadership, and decision making in the cockpit...

 (CRM) procedures are often used to ensure this communication process is efficient and clear, although this is not as prevalent as CRM for pilots
Aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...

.

Flight data / clearance delivery

Clearance Delivery is the position that issues route clearances to aircraft, typically before they commence taxiing. These contain details of the route that the aircraft is expected to fly after departure. Clearance Delivery or, at busy airports, the Traffic Management Coordinator (TMC) will, if necessary, coordinate with the en route center and national command center or flow control to obtain releases for aircraft. Often, however, such releases are given automatically or are controlled by local agreements allowing "free-flow" departures. When weather or extremely high demand for a certain airport or airspace becomes a factor, there may be ground "stops" (or "slot delays") or re-routes may be necessary to ensure the system does not get overloaded. The primary responsibility of Clearance Delivery is to ensure that the aircraft have the proper route and slot time. This information is also coordinated with the en route center and Ground Control in order to ensure that the aircraft reaches the runway in time to meet the slot time provided by the command center. At some airports, Clearance Delivery also plans aircraft pushbacks and engine starts, in which case it is known as the Ground Movement Planner (GMP): this position is particularly important at heavily congested airports to prevent taxiway and apron gridlock.

Flight Data (which is routinely combined with Clearance Delivery) is the position that is responsible for ensuring that both controllers and pilots have the most current information: pertinent weather changes, outages, airport ground delays/ground stops, runway closures, etc. Flight Data may inform the pilots using a recorded continuous loop on a specific frequency known as the Automatic Terminal Information Service
Automatic Terminal Information Service
Automatic Terminal Information Service, or ATIS, is a continuous broadcast of recorded noncontrol information in busier terminal areas. ATIS broadcasts contain essential information, such as weather information, which runways are active, available approaches, and any other information required by...

 (ATIS).

Approach and terminal control


Many airports have a radar control facility that is associated with the airport. In most countries, this is referred to as Terminal Control; in the U.S., it is referred to as a TRACON
Terminal Control Center
A terminal radar approach control is an air traffic control facility usually located within the vicinity of a large airport. Typically, the TRACON controls aircraft within a 20-50 nautical mile radius of the major airport and a number of "satellite airports" between surface and up to between and...

 (Terminal Radar Approach Control.) While every airport varies, terminal controllers usually handle traffic in a 30 to 50 nmi (55.6 to 92.6 km) radius from the airport. Where there are many busy airports close together, one consolidated TRACON
Terminal Control Center
A terminal radar approach control is an air traffic control facility usually located within the vicinity of a large airport. Typically, the TRACON controls aircraft within a 20-50 nautical mile radius of the major airport and a number of "satellite airports" between surface and up to between and...

 may service all the airports. The airspace boundaries and altitudes assigned to a TRACON
Terminal Control Center
A terminal radar approach control is an air traffic control facility usually located within the vicinity of a large airport. Typically, the TRACON controls aircraft within a 20-50 nautical mile radius of the major airport and a number of "satellite airports" between surface and up to between and...

, which vary widely from airport to airport, are based on factors such as traffic flows, neighboring airports and terrain. A large and complex example is the London Terminal Control Centre
London Terminal Control Centre
The London Terminal Control Centre was an air traffic control centre based in West Drayton, in the London Borough of Hillingdon, England, approximately 2.5 miles north of London Heathrow airport...

 which controls traffic for five main London airports up to 20000 feet (6,096 m) and out to 100 nautical miles (185.2 km).

Terminal controllers are responsible for providing all ATC services within their airspace. Traffic flow is broadly divided into departures, arrivals, and overflights. As aircraft move in and out of the terminal airspace, they are handed off to the next appropriate control facility (a control tower, an en-route control facility, or a bordering terminal or approach control). Terminal control is responsible for ensuring that aircraft are at an appropriate altitude when they are handed off, and that aircraft arrive at a suitable rate for landing.

Not all airports have a radar approach or terminal control available. In this case, the en-route center or a neighboring terminal or approach control may co-ordinate directly with the tower on the airport and vector inbound aircraft to a position from where they can land visually. At some of these airports, the tower may provide a non-radar procedural approach
Procedural control
Procedural control is a method of providing air traffic control services without the use of radar. It is used in regions of the world, specifically sparsely-populated land areas and oceans, where radar coverage is either prohibitively expensive or is simply not feasible...

 service to arriving aircraft handed over from a radar unit before they are visual to land. Some units also have a dedicated approach unit which can provide the procedural approach
Procedural control
Procedural control is a method of providing air traffic control services without the use of radar. It is used in regions of the world, specifically sparsely-populated land areas and oceans, where radar coverage is either prohibitively expensive or is simply not feasible...

 service either all the time or for any periods of radar outage for any reason.

En-route, center, or area control


ATC provides services to aircraft in flight between airports as well. Pilots fly under one of two sets of rules for separation: Visual Flight Rules
Visual flight rules
Visual flight rules are a set of regulations which allow a pilot to operate an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better than basic VFR weather minimums, as specified in the rules of the...

 (VFR) or Instrument Flight Rules
Instrument flight rules
Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....

 (IFR). Air traffic controllers have different responsibilities to aircraft operating under the different sets of rules. While IFR flights are under positive control, in the US VFR pilots can request flight following, which provides traffic advisory services on a time permitting basis and may also provide assistance in avoiding areas of weather and flight restrictions. In the UK, a pilot can request for "Basic Service", which is similar to flight following.

En-route air traffic controllers issue clearances and instructions for airborne aircraft, and pilots are required to comply with these instructions. En-route controllers also provide air traffic control services to many smaller airports around the country, including clearance off of the ground and clearance for approach to an airport. Controllers adhere to a set of separation standards that define the minimum distance allowed between aircraft. These distances vary depending on the equipment and procedures used in providing ATC services.

General characteristics

En-route air traffic controllers work in facilities called Area Control Centers, each of which is commonly referred to as a "Center". The United States uses the equivalent term Air Route Traffic Control Center (ARTCC). Each center is responsible for many thousands of square miles of airspace (known as a Flight Information Region
Flight Information Region
In aviation a flight information region is a region of airspace with specific dimensions, in which a flight information service and an alerting service are provided. It is the largest regular division of airspace in use in the world today....

) and for the airports within that airspace. Centers control IFR aircraft from the time they depart from an airport or terminal area's airspace to the time they arrive at another airport or terminal area's airspace. Centers may also "pick up" VFR aircraft that are already airborne and integrate them into the IFR system. These aircraft must, however, remain VFR until the Center provides a clearance.

Center controllers are responsible for climbing the aircraft to their requested altitude while, at the same time, ensuring that the aircraft is properly separated from all other aircraft in the immediate area. Additionally, the aircraft must be placed in a flow consistent with the aircraft's route of flight. This effort is complicated by crossing traffic, severe weather, special missions that require large airspace allocations, and traffic density. When the aircraft approaches its destination, the center is responsible for meeting altitude restrictions by specific points, as well as providing many destination airports with a traffic flow, which prohibits all of the arrivals being "bunched together". These "flow restrictions" often begin in the middle of the route, as controllers will position aircraft landing in the same destination so that when the aircraft are close to their destination they are sequenced.

As an aircraft reaches the boundary of a Center's control area it is "handed off" or "handed over" to the next Area Control Center. In some cases this "hand-off" process involves a transfer of identification and details between controllers so that air traffic control services can be provided in a seamless manner; in other cases local agreements may allow "silent handovers" such that the receiving center does not require any co-ordination if traffic is presented in an agreed manner. After the hand-off, the aircraft is given a frequency change and begins talking to the next controller. This process continues until the aircraft is handed off to a terminal controller ("approach").

Radar coverage

Since centers control a large airspace area, they will typically use long range radar that has the capability, at higher altitudes, to see aircraft within 200 nautical miles (370.4 km) of the radar antenna. They may also use TRACON radar data to control when it provides a better "picture" of the traffic or when it can fill in a portion of the area not covered by the long range radar.

In the U.S. system, at higher altitudes, over 90% of the U.S. airspace is covered by radar and often by multiple radar systems; however, coverage may be inconsistent at lower altitudes used by unpressurized aircraft due to high terrain or distance from radar facilities. A center may require numerous radar systems to cover the airspace assigned to them, and may also rely on pilot position reports from aircraft flying below the floor of radar coverage. This results in a large amount of data being available to the controller. To address this, automation systems have been designed that consolidate the radar data for the controller. This consolidation includes eliminating duplicate radar returns, ensuring the best radar for each geographical area is providing the data, and displaying the data in an effective format.

Centers also exercise control over traffic travelling over the world's ocean areas. These areas are also FIR
Flight Information Region
In aviation a flight information region is a region of airspace with specific dimensions, in which a flight information service and an alerting service are provided. It is the largest regular division of airspace in use in the world today....

s. Because there are no radar systems available for oceanic control, oceanic controllers provide ATC services using procedural control
Procedural control
Procedural control is a method of providing air traffic control services without the use of radar. It is used in regions of the world, specifically sparsely-populated land areas and oceans, where radar coverage is either prohibitively expensive or is simply not feasible...

. These procedures use aircraft position reports, time, altitude, distance, and speed to ensure separation. Controllers record information on flight progress strip
Flight progress strip
- General :A flight progress strip is a small strip of paper used to track a flight in air traffic control . While it has been supplemented by more technologically advanced methods of flight tracking since its introduction, it is still used in modern ATC as a quick way to annotate a flight, to...

s and in specially developed oceanic computer systems as aircraft report positions. This process requires that aircraft be separated by greater distances, which reduces the overall capacity for any given route. See for example the North Atlantic Track system.

Some Air Navigation Service Providers (e.g. Airservices Australia, The Federal Aviation Administration, NAV CANADA
NAV CANADA
Nav Canada is a privately run, not-for-profit corporation that owns and operates Canada's civil air navigation system .The company employs approximately 2,000 air traffic controllers , 800 flight service specialists and 700 technologists...

, etc.) have implemented Automatic Dependent Surveillance - Broadcast (ADS-B) as part of their surveillance capability. This new technology reverses the radar concept. Instead of radar "finding" a target by interrogating the transponder, the ADS-equipped aircraft sends a position report as determined by the navigation equipment on board the aircraft. Normally, ADS 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 is significant because it can be used where it is not possible to locate the infrastructure for a radar system (e.g. over water). Computerized radar displays are now being designed to accept ADS inputs as part of the display. This technology is currently used in portions of the North Atlantic and the Pacific by a variety of states who share responsibility for the control of this airspace.

Precision approach radars are commonly used by military controllers of airforces of several countries, to assist the Pilot in final phases of landing in places where Instrument Landing System and other sophisticated air borne equipements are unavailable to assist the pilots in marginal or near zero visibility conditions. This procedure is also called Talkdowns.

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 example, see this crash report.
RAS is also useful to technicians who are maintaining radar systems.

Flight traffic mapping

The mapping of flights in real-time is based on the air traffic control system. In 1991, data on the location of aircraft was made available by the Federal Aviation Administration to the airline industry. The National Business Aviation Association (NBAA), the General Aviation Manufacturers Association, the Aircraft Owners & Pilots Association, the Helicopter Association International, and the National Air Transportation Association petitioned the FAA to make ASDI information available on a "need-to-know" basis. Subsequently, NBAA advocated the broad-scale dissemination of air traffic data. The Aircraft Situational Display to Industry (ASDI) system now conveys up-to-date flight information to the airline industry and the public. Some companies that distribute ASDI information are FlightExplorer, FlightView, and FlyteComm. Each company maintains a website that provides free updated information to the public on flight status. Stand-alone programs are also available for displaying the geographic location of airborne IFR (Instrument Flight Rules) air traffic anywhere in the FAA air traffic system. Positions are reported for both commercial and general aviation traffic. The programs can overlay air traffic with a wide selection of maps such as, geo-political boundaries, air traffic control center boundaries, high altitude jet routes, satellite cloud and radar imagery.

Traffic

For more information see Air traffic flow management
Air traffic flow management
Air Traffic Flow Management is the regulation of air traffic in order to avoid exceeding airport or air traffic control capacity in handling traffic, and to ensure that available capacity is used efficiently....

.


The day-to-day problems faced by the air traffic control system are primarily related to the volume of air traffic demand placed on the system and weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...

. Several factors dictate the amount of traffic that can land at an airport in a given amount of time. Each landing aircraft must touch down, slow, and exit the runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...

 before the next crosses the approach end of the runway. This process requires at least one and up to four minutes for each aircraft. Allowing for departures between arrivals, each runway can thus handle about 30 arrivals per hour. A large airport with two arrival runways can handle about 60 arrivals per hour in good weather. Problems begin when airline
Airline
An airline provides air transport services for traveling passengers and freight. Airlines lease or own their aircraft with which to supply these services and may form partnerships or alliances with other airlines for mutual benefit...

s schedule more arrivals into an airport than can be physically handled, or when delays elsewhere cause groups of aircraft that would otherwise be separated in time to arrive simultaneously. Aircraft must then be delayed in the air by holding
Holding (aviation)
In aviation, holding is a maneuver designed to delay an aircraft already in flight while keeping it within a specified airspace.-Implementation:...

 over specified locations until they may be safely sequenced to the runway. Up until the 1990s, holding, which has significant environmental and cost implications, was a routine occurrence at many airports. Advances in computers now allow the sequencing of planes hours in advance. Thus, planes may be delayed before they even take off (by being given a "slot"), or may reduce speed in flight and proceed more slowly thus significantly reducing the amount of holding.

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. Paradoxically
Navigation paradox
The Navigation paradox states that increased navigational precision may result in increased collision risk. In the case of ships and aircraft, the advent of Global Positioning System navigation has enabled craft to follow navigational paths with such greater precision , that, without better...

, current high precision cruising altitude rules increase the risk of collision between 10 and 33 times over more sloppy alternatives when air traffic control errors occur.

Weather

Beyond runway capacity issues, weather is a major factor in traffic capacity. Rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...

, ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

 or snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...

 on the runway cause landing aircraft to take longer to slow and exit, thus reducing the safe arrival rate and requiring more space between landing aircraft. Fog
Fog
Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...

 also requires a decrease in the landing rate. These, in turn, increase airborne delay for holding aircraft. If more aircraft are scheduled than can be safely and efficiently held in the air, a ground delay program may be established, delaying aircraft on the ground before departure due to conditions at the arrival airport.

In Area Control Centers, a major weather problem is thunderstorms, which present a variety of hazards to aircraft. Aircraft will deviate around storms, reducing the capacity of the en-route system by requiring more space per aircraft, or causing congestion as many aircraft try to move through a single hole in a line of thunderstorms. Occasionally weather considerations cause delays to aircraft prior to their departure as routes are closed by thunderstorms.

Much money has been spent on creating software to streamline this process. However, at some ACCs, air traffic controllers still record data for each flight on strips of paper and personally coordinate their paths. In newer sites, these flight progress strip
Flight progress strip
- General :A flight progress strip is a small strip of paper used to track a flight in air traffic control . While it has been supplemented by more technologically advanced methods of flight tracking since its introduction, it is still used in modern ATC as a quick way to annotate a flight, to...

s have been replaced by electronic data presented on computer screens. As new equipment is brought in, more and more sites are upgrading away from paper flight strips.

Call signs

A prerequisite to safe air traffic separation is the assignment and use of distinctive call signs. These are permanently allocated by ICAO on request usually to scheduled flights and some air forces for military flights
Military aviation
Military aviation is the use of aircraft and other flying machines for the purposes of conducting or enabling warfare, including national airlift capacity to provide logistical supply to forces stationed in a theater or along a front. Air power includes the national means of conducting such...

. They are written callsigns with 3-letter combination like KLM, AAL, SWA, BAW, VLG followed by the flight number, like AAL872, VLG1011. As such they appear on flight plans and ATC radar labels. There are also the audio or Radio-telephony callsigns used on the radio contact between pilots and Air Traffic Control not always identical with the written ones. For example BAW symbolises British Airways but on the radio you will only hear the word Speedbird followed by an alpha-numeric code instead. By default, the callsign for any other flight is the registration number
Aircraft registration
An aircraft registration is a unique alphanumeric string that identifies a civil aircraft, in similar fashion to a licence plate on an automobile...

 (tail number) of the aircraft, such as "N12345", "C-GABC" or "EC-IZD". The term tail number is because a registration number is usually painted somewhere on the tail of a plane, yet this is not a rule. Registration numbers may appear on the engines, anywhere on the fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...

, and often on the wings. The short Radio-telephony callsigns for these tail numbers is the last 3 letters only like ABC spoken Alpha-Bravo-Charlie for C-GABC or the last 3 numbers like 345 spoken as TREE-FORE-FIFE for N12345. In the United States the abbreviation of callsigns is required to be a prefix (such as aircraft type, aircraft manufacturer, or first letter of registration) followed by the last three characters of the callsign. This abbreviation is only allowed after communications has been established in each sector.

The flight number part is decided by the aircraft operator. In this arrangement, an identical call sign might well be used for the same scheduled journey each day it is operated, even if the departure time varies a little across different days of the week. The call sign of the return flight often differs only by the final digit from the outbound flight. Generally, airline flight numbers are even if eastbound, and odd if westbound. In order to reduce the possibility of two callsigns on one frequency at any time sounding too similar, a number of airlines, particularly in Europe, have started using alphanumeric
Alphanumeric
Alphanumeric is a combination of alphabetic and numeric characters, and is used to describe the collection of Latin letters and Arabic digits or a text constructed from this collection. There are either 36 or 62 alphanumeric characters. The alphanumeric character set consists of the numbers 0 to...

 callsigns that are not based on flight numbers. For example DLH23LG, spoken as lufthansa
Lufthansa
Deutsche Lufthansa AG is the flag carrier of Germany and the largest airline in Europe in terms of overall passengers carried. The name of the company is derived from Luft , and Hansa .The airline is the world's fourth-largest airline in terms of overall passengers carried, operating...

-two-tree-lima-golf. Additionally it is the right of the air traffic controller to change the 'audio' callsign for the period the flight is in his sector if there is a risk of confusion, usually choosing the tail number instead.

Before around 1980 International Air Transport Association
International Air Transport Association
The International Air Transport Association is an international industry trade group of airlines headquartered in Montreal, Quebec, Canada, where the International Civil Aviation Organization is also headquartered. The executive offices are at the Geneva Airport in SwitzerlandIATA's mission is to...

 (IATA) and ICAO were using the same 2-letter callsigns. Due to the larger number of new airlines after deregulation ICAO established the 3-letter callsigns as mentioned above. The IATA callsigns are currently used in aerodromes on the announcement tables but never used any longer in Air Traffic Control. For example, AA is the IATA callsign for American Airlines
American Airlines
American Airlines, Inc. is the world's fourth-largest airline in passenger miles transported and operating revenues. American Airlines is a subsidiary of the AMR Corporation and is headquartered in Fort Worth, Texas adjacent to its largest hub at Dallas/Fort Worth International Airport...

 — ATC equivalent AAL. Other examples include LY/ELY for El Al
El Al
El Al Israel Airlines Ltd , trading as El Al , is the flag carrier of Israel. It operates scheduled domestic and international services and cargo flights to Europe, North America, Africa and the Far East from its main base in Ben Gurion International Airport...

, DL/DAL for Delta Air Lines
Delta Air Lines
Delta Air Lines, Inc. is a major airline based in the United States and headquartered in Atlanta, Georgia. The airline operates an extensive domestic and international network serving all continents except Antarctica. Delta and its subsidiaries operate over 4,000 flights every day...

, VY/VLG for Vueling Airlines
Vueling Airlines
Vueling Airlines SA , commonly shortened to Vueling, is an airline based in El Prat de Llobregat, near Barcelona , where it maintains its main operating base...

, etc.

Technology

Many technologies are used in air traffic control systems. Primary and secondary radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

 are used to enhance a controller's situation awareness
Situation awareness
Situation awareness, situational awareness, or SA, is the perception of environmental elements with respect to time and/or space, the comprehension of their meaning, and the projection of their status after some variable has changed, such as time...

 within his assigned airspace — all types of aircraft send back primary echoes of varying sizes to controllers' screens as radar energy is bounced off their skins, and transponder
Transponder
In telecommunication, the term transponder has the following meanings:...

-equipped aircraft reply to secondary radar interrogations by giving an ID (Mode A), an altitude (Mode C) and/or a unique callsign (Mode S). Certain types of weather may also register on the radar screen.

These inputs, added to data from other radars, are correlated to build the air situation. Some basic processing occurs on the radar tracks, such as calculating ground speed and magnetic headings.

Usually, a Flight Data Processing System manages all the flight plan
Flight plan
Flight plans are documents filed by pilots or a Flight Dispatcher with the local Civil Aviation Authority prior to departure...

 related data, incorporating - in a low or high degree - the information of the track once the correlation between them (flight plan and track) is established. All this information is distributed to modern operational display system
Operational display system
Operational Display Systems refers to systems used for tracking the status of multiple objects in avionics. Operational Displays Systems are usually being developed by large countries' civil aviation authorities Operational Display Systems refers to systems used for tracking the status of multiple...

s, making it available to controllers.

The FAA
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 has spent over USD$3 billion on software, but a fully automated system is still over the horizon. In 2002 the UK brought a new area control centre into service at Swanwick
Swanwick, Hampshire
Swanwick is a village in Hampshire, England, east of the River Hamble and north of the M27 motorway.The village is located within the borough of Fareham and is the site of the London Area Control Centre and the London Terminal Control Centre part of National Air Traffic Services Air Traffic...

, in Hampshire
Hampshire
Hampshire is a county on the southern coast of England in the United Kingdom. The county town of Hampshire is Winchester, a historic cathedral city that was once the capital of England. Hampshire is notable for housing the original birthplaces of the Royal Navy, British Army, and Royal Air Force...

, relieving a busy suburban centre at West Drayton
West Drayton
West Drayton is a suburban area in the London Borough of Hillingdon in the far west of London, England. Formerly part of the Yiewsley and West Drayton Urban District of Middlesex, the district became part of Greater London in 1965....

 in Middlesex
Middlesex
Middlesex is one of the historic counties of England and the second smallest by area. The low-lying county contained the wealthy and politically independent City of London on its southern boundary and was dominated by it from a very early time...

, north of London Heathrow Airport
London Heathrow Airport
London Heathrow Airport or Heathrow , in the London Borough of Hillingdon, is the busiest airport in the United Kingdom and the third busiest airport in the world in terms of total passenger traffic, handling more international passengers than any other airport around the globe...

. Software from Lockheed-Martin predominates at Swanwick. However, Swanwick
Swanwick
Swanwick may refer to:* The village of Swanwick, Derbyshire, England.* The village of Swanwick, Hampshire, England.* Helena Swanwick , British feminist and pacifist....

 was initially troubled by software and communications problems causing delays and occasional shutdowns.

Some tools are available in different domains to help the controller further:
  • Flight Data Processing Systems: this is the system (usually one per Center) that processes all the information related to the Flight (the Flight Plan), typically in the time horizon from Gate to gate (airport departure/arrival gates). It uses such processed information to invoke other Flight Plan related tools (such as e.g. MTCD), and distributes such processed information to all the stakeholders (Air Traffic Controllers, collateral Centers, Airports, etc.).
  • Short Term Conflict Alert
    Short Term Conflict Alert
    Short Term Conflict Alert is an automated warning system for air traffic controllers . It is a ground-based safety net intended to assist the controller in preventing collision between aircraft by generating, in a timely manner, an alert of a potential or actual infringement of separation minima.-...

     (STCA) that checks possible conflicting trajectories in a time horizon of about 2 or 3 minutes (or even less in approach context - 35 seconds in the French Roissy & Orly approach centres ) and alerts the controller prior to the loss of separation. The algorithms used may also provide in some systems a possible vectoring solution, that is, the manner in which to turn, descend, or climb the aircraft in order to avoid infringing the minimum safety distance or altitude clearance.
  • Minimum Safe Altitude Warning
    Minimum Safe Altitude Warning
    Minimum Safe Altitude Warning is an automated warning system for air traffic controllers . It is a ground-based safety net intended to warn the controller about increased risk of controlled flight into terrain accidents by generating, in a timely manner, an alert of aircraft proximity to terrain...

     (MSAW): a tool that alerts the controller if an aircraft appears to be flying too low to the ground or will impact terrain based on its current altitude and heading.
  • System Coordination (SYSCO) to enable controller to negotiate the release of flights from one sector to another.
  • Area Penetration Warning (APW) to inform a controller that a flight will penetrate a restricted area.
  • Arrival and Departure Manager to help sequence the takeoff and landing of aircraft.
    • The Departure Manager (DMAN)
      DMAN
      DMAN, also known as Departure Manager is a planning tool developed to improve the departure flows at airports and increase the predictability. DMAN calculates the Target Take Off Times and the Target Startup Approval Times taking multiple constraints and preferences into account...

      : A system aid for the ATC at airports, that calculates a planned departure flow with the goal to maintain an optimal throughput at the runway, reduce queuing at holding point and distribute the information to various stakeholders at the airport (i.e. the airline, ground handling and Air Traffic Control (ATC)).
    • The Arrival Manager (AMAN)
      Aman
      -External links:*...

      : A system aid for the ATC at airports, that calculates a planned Arrival flow with the goal to maintain an optimal throughput at the runway, reduce arrival queuing and distribute the information to various stakeholders.
    • passive Final Approach Spacing Tool (pFAST), a CTAS tool, provides runway assignment and sequence number advisories to terminal controllers to improve the arrival rate at congested airports. pFAST was deployed and operational at five US TRACONs before being cancelled. NASA research included an Active FAST capability that also provided vector and speed advisories to implement the runway and sequence advisories.
  • Converging Runway Display Aid (CRDA) enables Approach controllers to run two final approaches that intersect and make sure that go arounds are minimized
  • Center TRACON Automation System (CTAS) is a suite of human centered decision support tools developed by NASA Ames Research Center. Several of the CTAS tools have been field tested and transitioned to the FAA for operational evaluation and use. Some of the CTAS tools are: Traffic Management Advisor (TMA), passive Final Approach Spacing Tool (pFAST), Collaborative Arrival Planning (CAP), Direct-To (D2), En Route Descent Advisor (EDA) and Multi Center TMA. The software is running on linux.
  • Traffic Management Advisor (TMA), a CTAS tool, is an en route decision support tool that automates time based metering solutions to provide an upper limit of aircraft to a TRACON from the Center over a set period of time. Schedules are determined that will not exceed the specified arrival rate and controllers use the scheduled times to provide the appropriate delay to arrivals while in the en route domain. This results in an overall reduction in en route delays and also moves the delays to more efficient airspace (higher altitudes) than occur if holding near the TRACON boundary is required to not overload the TRACON controllers. TMA is operational at most en route air route traffic control centers (ARTCCs) and continues to be enhanced to address more complex traffic situations (e.g. Adjacent Center Metering (ACM) and En Route Departure Capability (EDC))
  • MTCD & URET
    • In the US, User Request Evaluation Tool (URET) takes paper strips out of the equation for En Route controllers at ARTCCs by providing a display that shows all aircraft that are either in or currently routed into the sector.
    • In Europe, several MTCD tools are available: iFACTS (NATS
      National Air Traffic Services
      NATS Ltd. is the main air navigation service provider in the United Kingdom. It provides en-route air traffic control services to flights within the UK Flight Information Regions and the Shanwick Oceanic Control Area, and provides air traffic control services to fifteen UK airports and Gibraltar...

      ), VAFORIT (DFS
      Deutsche Flugsicherung
      The Deutsche Flugsicherung is the company in charge of air traffic control for Germany. It is a company organized under private law and 100% owned by the Federal Republic of Germany. Since 1994, DFS has been responsible for handling both civil and military air traffic in peacetime, removing a...

      ), New FDPS (MASUAC). The SESAR
      Single European Sky ATM Research
      Single European Sky ATM Research is the name given to the collaborative project that is intended to completely overhaul the European airspace and its Air Traffic Management .- Project :The SESAR project is composed of three phases :...

       Programme should soon launch new MTCD concepts.
URET and MTCD provide conflict advisories up to 30 minutes in advance and have a suite of assistance tools that assist in evaluating resolution options and pilot requests.
  • Mode S: provides a data downlink of flight parameters via Secondary Surveillance Radars allowing radar processing systems and therefore controllers to see various data on a flight, including airframe unique id (24-bits encoded), indicated airspeed and flight director selected level, amongst others.
  • CPDLC: Controller Pilot Data Link Communications
    Controller Pilot Data Link Communications
    Controller Pilot Data Link Communications , also referred to as Controller Pilot Data Link , is a method by which air traffic controllers can communicate with pilots over a datalink system.-Necessity:...

     — allows digital messages to be sent between controllers and pilots, avoiding the need to use radiotelephony. It is especially useful in areas where difficult-to-use HF
    High frequency
    High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...

     radiotelephony was previously used for communication with aircraft, e.g. oceans. This is currently in use in various parts of the world including the Atlantic and Pacific oceans.
  • ADS-B: Automatic Dependent Surveillance Broadcast — provides a data downlink of various flight parameters to air traffic control systems via the Transponder (1090 MHz) and reception of those data by other aircraft in the vicinity. The most important is the aircraft's latitude, longitude and level: such data can be utilized to create a radar-like display of aircraft for controllers and thus allows a form of pseudo-radar control to be done in areas where the installation of radar is either prohibitive on the grounds of low traffic levels, or technically not feasible (e.g. oceans). This is currently in use in Australia, Canada and parts of the Pacific Ocean and Alaska.
  • The Electronic Flight Strip system (e-strip): A system of electronic flight strips replacing the old paper strips is being used by several Service Providers, such as NAV CANADA, MASUAC, DFS, being produced by several industries, such as Indra Sistemas, Thales Group
    Thales Group
    The Thales Group is a French electronics company delivering information systems and services for the aerospace, defense, transportation and security markets...

    , Frequentis
    Frequentis
    Frequentis is an austrian high-tech company that develops communication and information solutions for safety-critical applications. It offers its control centre solutions, products and services world-wide to a broad range of customers acting in various mission-critical fields...

    , Avibit, SAAB etc. E-strips allows controllers to manage electronic flight data online without Paper Strips, reducing the need for manual functions.
  • Screen Content Recording: Hardware or software based recording function which is part of most modern Automation System and that captures the screen content shown to of the ATCO. Such recordings are used for a later replay together with audio recording for investigations and post event analysis.
  • Communication Navigation Surveillance / Air Traffic Management (CNS/ATM) systems are communications, navigation, and surveillance systems, employing digital technologies, including satellite systems together with various levels of automation, applied in support of a seamless global air traffic management system.

Air navigation service providers (ANSPs) and traffic service providers (ATSPs)

The regulatory function remains the responsibility of the State and can be exercised by Government and/or independent Safety, Airspace and Economic Regulators depending on the national institutional arrangements. Often you will see a division between the Civil Aviation Authority
Civil Aviation Authority
This is a list of national and supra-national civil aviation authorities.-See also:* Air route authority between the United States and the People's Republic of China* National Transportation Safety Board -External links:****...

 (CAA) (the Regulator) and the ANSP (the Air Navigation Service Provider
Air Navigation Service Provider
An Air Navigation Service Provider is the organisation that separates aircraft on the ground or in flight in a dedicated block of airspace on behalf of a state or a number of states....

).

An Air Navigation Service Provider — The air navigation service provider is the authority directly responsible for providing both visual and non-visual aids to navigation within a specific airspace in compliance with, but not limited to, International Civil Aviation Organization (ICAO) Annexes 2, 6, 10 and 11; ICAO Documents 4444 and 9426; and, other international, multi-national, and national policy, agreements or regulations.

An Air Traffic Service Provider is the relevant authority designated by the State responsible for providing air traffic services in the airspace concerned. Air traffic services is generic and can mean: flight information service
Flight Information Service
A flight information service is a form of air traffic service which is available to any aircraft within a flight information region , as agreed internationally by ICAO....

, alerting service, air traffic advisory service, air traffic control service (area control service, approach control service or aerodrome control service), etc.

Both ANSPs and ATSPs can be public, private or corporatized organisations and examples of the different legal models exist throughout the world today. The world's ANSPs are united in and represented by the Civil Air Navigation Services Organisation
Civil Air Navigation Services Organisation
CANSO – The Civil Air Navigation Services Organisation – is the global voice of the companies that provide air traffic control, and represents the interests of Air Navigation Service Providers worldwide...

 (CANSO) based at Amsterdam Airport Schiphol in the Netherlands.

In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, the Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 (FAA) provides this service to all aircraft in the National Airspace System
National Airspace System
The National Airspace System of the United States is one of the most complex aviation systems in the world — consisting of thousands of people, procedures, facilities, and pieces of equipment — that enables safe and expeditious air travel in the United States and over large portions of the world's...

 (NAS). With the exception of facilities operated by the Department of Defense
United States Department of Defense
The United States Department of Defense is the U.S...

 (DoD), the FAA is responsible for all aspects of U.S.A Air Traffic Control including hiring and training controllers, although there are contract towers located in many parts of the country. A contract tower is an Airport Traffic Control Tower (ATCT) that performs the same function as an FAA-run ATCT but is staffed by employees of a private company (Martin State Airport
Martin State Airport
Martin State Airport is a public use airport located nine nautical miles east of the central business district of Baltimore, in Baltimore County, Maryland, United States...

 in Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

 is an example). DoD facilities are generally staffed by military personnel and operate separately but concurrently with FAA facilities, under similar rules and procedures. In Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, Air Traffic Control is provided by NAV CANADA
NAV CANADA
Nav Canada is a privately run, not-for-profit corporation that owns and operates Canada's civil air navigation system .The company employs approximately 2,000 air traffic controllers , 800 flight service specialists and 700 technologists...

, a private, non-share capital corporation that operates Canada's civil air navigation service.
- Agjencia Nacionale e Trafikut Ajror - Armenian Air Traffic Services (ARMATS) - Austro Control - Airservices Australia
Airservices Australia
Airservices Australia is an Australian Government agency, responsible for providing safe and environmentally sound air traffic control management and related airside services to the aviation industry within the Australian Flight Information Region...

 (State Owned Corporation) and Royal Australian Air Force
Royal Australian Air Force
The Royal Australian Air Force is the air force branch of the Australian Defence Force. The RAAF was formed in March 1921. It continues the traditions of the Australian Flying Corps , which was formed on 22 October 1912. The RAAF has taken part in many of the 20th century's major conflicts...

. - Republican Unitary Enterprise "Белаэронавигация (Belarusian Air Navigation)" - Belgocontrol - Departmento de Controle de Tráfego Aéreo (Military Authority) and ANAC - Agência Nacional de Aviação Civil - Air Traffic Services Authority - NAV CANADA
NAV CANADA
Nav Canada is a privately run, not-for-profit corporation that owns and operates Canada's civil air navigation system .The company employs approximately 2,000 air traffic controllers , 800 flight service specialists and 700 technologists...

 - formerly provided by Transport Canada
Transport Canada
Transport Canada is the department within the government of Canada which is responsible for developing regulations, policies and services of transportation in Canada. It is part of the Transportation, Infrastructure and Communities portfolio...

 and Canadian Forces
Canadian Forces
The Canadian Forces , officially the Canadian Armed Forces , are the unified armed forces of Canada, as constituted by the National Defence Act, which states: "The Canadian Forces are the armed forces of Her Majesty raised by Canada and consist of one Service called the Canadian Armed Forces."...


} - DGAC (Dirección General de Aeronáutica Civil)
}
}
}
} - Dirección General de Aviación Civil
} - (UAEAC) Aeronáutica Civil Colombiana - Hrvatska kontrola zračne plovidbe (Croatia Control Ltd.) - IACC (Instituto de Aeronáutica Civil de Cuba) - Řízení letového provozu ČR - Naviair (Danish ATC) - IDAC (Instituto Dominicano de Aviación Civil) "Dominican Institute of Civil Aviation" - Estonian Air Navigation Services - Eurocontrol - (European Organisation for the Safety of Air Navigation) - Finavia
Finavia
Finavia Corporation , the former Finnish Civil Aviation Administration, is the managing body of 25 airports located in Finland. Finavia maintains the airport network as well as the navigation system. Finavia's customers are both the travel industry as well as air passengers...

 - Direction Générale de l'Aviation Civile (DGAC) : Direction des Services de la Navigation Aérienne (DSNA) (Government body) - SAKAERONAVIGATSIA, Ltd. (Georgian Air Navigation) - Deutsche Flugsicherung
Deutsche Flugsicherung
The Deutsche Flugsicherung is the company in charge of air traffic control for Germany. It is a company organized under private law and 100% owned by the Federal Republic of Germany. Since 1994, DFS has been responsible for handling both civil and military air traffic in peacetime, removing a...

 (German ATC - State-owned company) - Hellenic Civil Aviation Authority
Hellenic Civil Aviation Authority
The Hellenic Civil Aviation Authority , abbreviated HCAA , is a department of the Greek Government under the Ministry of Transportation and Communications...

 (HCAA) - CAD (Civil Aviation Department) - HungaroControl Magyar Légiforgalmi Szolgálat Zrt. (HungaroControl Hungarian Air Navigation Services Pte. Ltd. Co.) - ISAVIA - Angkasa Pura II - IAA (Irish Aviation Authority
Irish Aviation Authority
The Irish Aviation Authority is a commercial semi state company employing approximately 700 people at six locations around Ireland. The IAA has two main functions; the provision of air traffic management & related services in Irish controlled airspace and the safety regulation of the civil...

) - Airports Authority of India
Airports Authority of India
The Airports Authority of India is an organization working under the Ministry of Civil Aviation that manages most of the airports in India. The AAI manages and operates 126 airports including 16 international airports, 89 domestic airports and 26 civil enclaves. The corporate headquarters are at...

 (AAI) (under Ministry of Civil Aviation, Government Of India
Government of India
The Government of India, officially known as the Union Government, and also known as the Central Government, was established by the Constitution of India, and is the governing authority of the union of 28 states and seven union territories, collectively called the Republic of India...

) - ENAV (Italian ATC)(Ente Nazionale Assistenza al Volo - Italian ATC) - JCAA (Jamaica Civil Aviation Authority) - LGS (Latvian ATC) - ANS (Lithuanian ATC) - Luxembourg ATC - DGCA (Macedonian ATC) - DCA-Department of Civil Aviation - Malta Air Traffic Services Ltd - Servicios a la Navegación en el Espacio Aéreo Mexicano - Civil Aviation Authority of Nepal - Luchtverkeersleiding Nederland (LVNL) (Dutch ATC) http://www.eurocontrol.nl Eurocontrol (European area control ATC) - Airways New Zealand
Airways New Zealand
Airways New Zealand is the sole Air Traffic Service provider in New Zealand.The company was created 1987 as a State-Owned Enterprise having formerly being a division of the Ministry of Transport, a government department. This followed the recommendations of the 1986 Mason-Morris Review...

 (State Owned Enterprise) - Avinor
Avinor
Avinor AS is a state owned limited company in that operates most of the civil airports in Norway. The Norwegian state, via the Norwegian Ministry of Transport and Communications controls 100 percent of the share capital. Avinor was created on 1 January 2003, by the privatization of the...

 (State-owned private company) - Civil Aviation Authority (under Government of Pakistan
Government of Pakistan
The Government of Pakistan is a federal parliamentary system, with an indirectly-elected President as the Head of State and Commander in Chief of the Pakistani Armed Forces, and an indirectly-elected Prime Minister as the Head of Government. The President’s appointment and term are...

) - Centro de Instrucción de Aviación Civil CIAC Civil Aviation Training Center - Civil Aviation Authority of the Philippines (CAAP) (under the Philippine Government) - PANSA - Polish Air Navigation Services Agency - NAV - NAV (Portuguese ATC) - Romanian Air Traffic Services Administration - (ROMATSA) - Federal State Unitary Enterprise "State ATM Corporation" - (State ATM Corporation) - General Authority of Civil Aviation (GACA) - CAAS (Civil Aviation Authority of Singapore
Civil Aviation Authority of Singapore
The Civil Aviation Authority of Singapore is Singapore's Civil Aviation Authority and a statutory board under the Ministry of Transport of the Singapore Government...

) - Serbia and Montenegro Air Traffic Services Agency
Serbia and Montenegro Air Traffic Services Agency
Serbia and Montenegro Air Traffic Services Agency is the regional air traffic control center of Serbia, Montenegro and 55% of Bosnia and Herzegovina ....

 Ltd. (SMATSA) - Letové prevádzkové služby Slovenskej republiky - Slovenia Control - Air Traffic and Navigation Services. (ATNS) - AENA
Aena
Aeropuertos Españoles y Navegación Aérea , literally "Spanish Airports and Air Navigation", is the Spanish public body that owns and operates the majority of airports in Spain, with the exceptions of the private owned Ciudad Reals and Lleida-Alguaire Airport. Aena is also responsible for Air...

 (Spanish ATC and Airports) - The LFV Group (Swedish ATC) - Skyguide
Skyguide
skyguide is the air navigation services company that controls Swiss airspace....

 - ANWS Civil Aeronautical Administration - AEROTHAI (Aeronautical Radio of Thailand) - TTCAA (Trinidad and Tobago Civil Aviation Authority) - DGCA (Turkish Directorate General of Civil Aviation) - General Civil Aviation Authority (GCAA) - National Air Traffic Services
National Air Traffic Services
NATS Ltd. is the main air navigation service provider in the United Kingdom. It provides en-route air traffic control services to flights within the UK Flight Information Regions and the Shanwick Oceanic Control Area, and provides air traffic control services to fifteen UK airports and Gibraltar...

 (49% State Owned Public-Private Partnership) - Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 (Government Body) - Ukrainian State Air Traffic Service Enterprise (UkSATSE) - INAC (Instituto Nacional de Aviación Civil)

Proposed changes

In the United States, some alterations to traffic control procedures are being examined.
  • The Next Generation Air Transportation System
    Next Generation Air Transportation System
    The Next Generation Air Transportation System is the name given to a new National Airspace System due for implementation across the United States in stages between 2012 and 2025. The...

     examines how to overhaul the United States national airspace system.
  • Free flight
    Free flight (air traffic control)
    Free flight is a developing air traffic control method that uses no centralized control . Instead, parts of airspace are reserved dynamically and automatically in a distributed way using computer communication to ensure the required separation between aircraft. This new system may be implemented...

     is a developing air traffic control method that uses no centralized control (e.g. air traffic controllers). Instead, parts of airspace are reserved dynamically and automatically in a distributed way using computer communication to ensure the required separation between aircraft.


In Europe, the SESAR (Single European Sky ATM Research
Single European Sky ATM Research
Single European Sky ATM Research is the name given to the collaborative project that is intended to completely overhaul the European airspace and its Air Traffic Management .- Project :The SESAR project is composed of three phases :...

) Programme plans to develop new methods, new technologies, new procedures, new systems to accommodate future (2020 and beyond) Air Traffic Needs.

Many countries have also privatized or corporatized their air navigation service providers.

Change in regulation in admittance for possible A.T.C.'s regarding their eye-refraction and correction thereof by technology has been proposed.

ATC regulations in the United States

FAA Control Tower Operators (CTO)/Air Traffic Controller
Air traffic controller
Air traffic controllers are the people who expedite and maintain a safe and orderly flow of air traffic in the global air traffic control system. The position of the air traffic controller is one that requires highly specialized skills...

s use FAA Order 7110.65T as the authority for all procedures regarding air traffic. For more information regarding Air Traffic Control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...

 rules and regulations, refer the Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

's (FAA) website.

See also

  • Air safety
    Air safety
    Air safety is a term encompassing the theory, investigation and categorization of flight failures, and the prevention of such failures through regulation, education and training. It can also be applied in the context of campaigns that inform the public as to the safety of air travel.-United...

  • Air traffic controller
    Air traffic controller
    Air traffic controllers are the people who expedite and maintain a safe and orderly flow of air traffic in the global air traffic control system. The position of the air traffic controller is one that requires highly specialized skills...

  • Airspace
    Airspace
    Airspace means the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere....

  • Area Control Center
    Area Control Center
    In air traffic control, an Area Control Center , also known as a Center, is a facility responsible for controlling instrument flight rules aircraft en route in a particular volume of airspace at high altitudes between airport approaches and departures...

     (ACC)
  • Automatic dependent surveillance-broadcast
    Automatic dependent surveillance-broadcast
    Automatic Dependent Surveillance-Broadcast is a surveillance technology for tracking aircraft as part of the Next Generation Air Transportation System ...

     (ADS-B)
  • Aviation light signals
    Aviation light signals
    In the case of a radio failure or aircraft not equipped with a radio, air traffic control may use a signal lamp to direct the aircraft. The signal lamp has a focused bright beam and is capable of emitting three different colors: red, white and green. These colors may be flashed or steady, and have...

  • Bashkirian Airlines Flight 2937 & DHL Flight 611 mid-air collision
  • Civil Air Navigation Services Organisation
    Civil Air Navigation Services Organisation
    CANSO – The Civil Air Navigation Services Organisation – is the global voice of the companies that provide air traffic control, and represents the interests of Air Navigation Service Providers worldwide...

  • Flight level
    Flight level
    A Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...

     (FL)
  • Forward Air Controller
  • Flight Information Service Officer
    Flight Information Service Officer
    Flight information service officers or FISO, provide a Flight Information Service to any air traffic that requests it, or requires it. A FISO is a licensed operator, who most usually works at an aerodrome, although there are some FISOs working in Area Control Centers. FISOs must been validated for...

  • Flight planning
    Flight planning
    Flight planning is the process of producing a flight plan to describe a proposed aircraft flight. It involves two safety-critical aspects: fuel calculation, to ensure that the aircraft can safely reach the destination, and compliance with air traffic control requirements, to minimise the risk of...

  • Flight tracking
  • Flight progress strip
    Flight progress strip
    - General :A flight progress strip is a small strip of paper used to track a flight in air traffic control . While it has been supplemented by more technologically advanced methods of flight tracking since its introduction, it is still used in modern ATC as a quick way to annotate a flight, to...

  • Flight traffic mapping
    Flight traffic mapping
    ]Flight Traffic Mapping uses animation to depict flight traffic. The mapping of flights in real-time is based on a sophisticated air traffic control system that was developed for North America. The air traffic control system is a complex combination of electronics and people that helps guide planes...

  • Global Air Traffic Management
    Global Air Traffic Management
    Global air-traffic management is a concept for satellite-based communication, navigation, surveillance and air traffic management. The Federal Aviation Administration and the International Civil Aviation Organization, a special agency of the United Nations, established GATM standards to keep air...

  • IFATCA (International Federation of ATC Associations)
  • Navigation
    Navigation
    Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...

  • Professional Air Traffic Controllers Organization
    Professional Air Traffic Controllers Organization
    The Professional Air Traffic Controllers Organization or PATCO was a United States trade union that operated from 1968 until its decertification in 1981 following a strike that was broken by the Reagan Administration. The 1981 strike and defeat of PATCO has been called "one of the most important...

  • Remote and Virtual Tower
    Remote and Virtual Tower
    Remote and Virtual Tower is a new concept where the Air Traffic Service at an airport is performed somewhere else than in the local control tower.-Concept:...

  • Tenerife disaster
    Tenerife disaster
    The Tenerife airport disaster occurred on March 27, 1977, when two Boeing 747 passenger aircraft collided on the runway of Los Rodeos Airport on the Spanish island of Tenerife, one of the Canary Islands...

    , (TFN
    Los Rodeos Airport
    -Statistics:-Accidents and incidents:Tenerife North Airport was the scene of the Tenerife airport disaster, to date the worst accident in aviation history. The accident took place on 27 March 1977, when, during take-off, the Boeing 747 of KLM Flight 4805 crashed into the Boeing 747 of Pan Am Flight...

    )
  • Terminal Control Center
    Terminal Control Center
    A terminal radar approach control is an air traffic control facility usually located within the vicinity of a large airport. Typically, the TRACON controls aircraft within a 20-50 nautical mile radius of the major airport and a number of "satellite airports" between surface and up to between and...

  • Tower en route control
    Tower en route control
    In United States aviation, tower en route control is a collection of published low-altitude, short-distance IFR routes through large metropolitan areas that require no level of air traffic control higher than approach-control facilities....

     (TEC)
  • Virtual Air Traffic Simulation Network (VATSIM)
  • Zagreb mid-air collision

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