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102-582: A flight through the NAS typically begins and ends at an airport which may be controlled (by a tower ) or uncontrolled. On departure, the aircraft is in one of five of the six classes of airspace administered by the Federal Aviation Administration (FAA), and different flight rules apply to each class. Depending on the class of airspace and flight conditions, communication with air traffic controllers may or may not be required. Operation of each flight

204-568: A quarter meridian . So ⁠ 10,000,000 m / 90 × 60 ⁠ = 1,851.85 m ≈ 1,852 m became the metric length for a nautical mile. France made it legal for the French Navy in 1906, and many metric countries voted to sanction it for international use at the 1929 International Hydrographic Conference. Both the United States and the United Kingdom used an average arcminute—specifically,

306-413: A ' Flight Information Service ', which is similar to flight following. In the United Kingdom, it is known as a 'basic service'. 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

408-466: A 36 feet long by 66-foot (11 by 20-meter) demilitarised MQ-9 Predator for the first time through the NAS with no chase aircraft and controlled from Armstrong Flight Research Center , towards unmanned aircraft operations in civil airspace. In the U.S., airspace consists of classes A, B, C, D, E, and G. The NAS includes both controlled and uncontrolled airspace. Class A begins and includes 18,000 ft. MSL and continues up to 60,000 ft. MSL. It

510-400: 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 centre or a neighbouring terminal or approach control may co-ordinate directly with

612-433: 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 has the correct aerodrome information, such as weather and airport conditions, the correct route after departure, and time restrictions relating to that flight. This information

714-410: A controlled airspace. Under visual flight conditions, Class E can be considered uncontrolled airspace. Airports without operational control towers are uncontrolled airfields. Pilots in these areas are responsible for position and separation and may use a specified Common Traffic Advisory Frequency (CTAF) or UNICOM for that airport, although no-radio flight is also permitted. Class G airspace

816-416: A controller can review the last radar returns from the aircraft to determine its likely position. For an example, see the crash report in the following citation. RAS is also useful to technicians who are maintaining radar systems. The mapping of flights in real-time is based on the air traffic control system, and volunteer ADS-B receivers. In 1991, data on the location of aircraft was made available by

918-417: A cumulative nine months on strike between 2004 and 2016. Nautical mile A nautical mile is a unit of length used in air, marine, and space navigation , and for the definition of territorial waters . Historically, it was defined as the meridian arc length corresponding to one minute ( ⁠ 1 / 60 ⁠ of a degree) of latitude at the equator, so that Earth's polar circumference

1020-406: A degree (5866 ⁠ 2 / 3 ⁠ feet per arcminute ). In 1633, William Oughtred suggested 349,800 feet to a degree (5830 feet per arcminute). Both Gunter and Oughtred put forward the notion of dividing a degree into 100 parts, but their proposal was generally ignored by navigators. The ratio of 60 miles, or 20 leagues, to a degree of latitude remained fixed while the length of the mile

1122-485: A degree is not explained. Eventually, the ratio of 60 miles to a degree appeared in English in a 1555 translation of Pietro Martire d'Anghiera 's Decades: "[Ptolemy] assigned likewise to every degree three score miles." By the late 16th century English geographers and navigators knew that the ratio of distances at sea to degrees was constant along any great circle (such as the equator , or any meridian), assuming that Earth

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1224-400: A distance of 100 nautical miles (185 kilometres; 115 miles). 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

1326-432: 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 kilometres; 230 miles) of the radar antenna. They may also use 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

1428-414: 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. Centres also exercise control over traffic travelling over

1530-571: A minute of arc of a great circle of a sphere having the same surface area as the Clarke 1866 ellipsoid . The authalic (equal area) radius of the Clarke 1866 ellipsoid is 6,370,997.2 metres (20,902,222 ft). The resulting arcminute is 1,853.2480 metres (6,080.210 ft). The United States chose five significant digits for its nautical mile, 6,080.2 feet , whereas the United Kingdom chose four significant digits for its Admiralty mile, 6,080 feet. In 1929

1632-714: A new area control centre into service at the London Area Control Centre (LACC) at Swanwick in Hampshire, relieving a busy suburban centre at West Drayton in Middlesex, north of London Heathrow Airport . Software from Lockheed-Martin predominates at the London Area Control Centre. However, the centre was initially troubled by software and communications problems causing delays and occasional shutdowns. Some tools are available in different domains to help

1734-468: A number of airlines, particularly in Europe, have started using alphanumeric call signs that are not based on flight numbers (e.g. DLH23LG, spoken as Lufthansa -two-three-lima-golf , to prevent confusion between incoming DLH23 and outgoing DLH24 in the same frequency). Additionally, it is the right of the air traffic controller to change the 'audio' call sign for the period the flight is in his sector if there

1836-400: A previous edition of Geography states " unul gradul log. et latitud sub equinortiali formet stadia 500 que fanut miliaria 62 ⁠ 1 / 2 ⁠ " ("one degree longitude and latitude under the equator forms 500 stadia , which make 62 ⁠ 1 / 2 ⁠ miles"). Whether a correction or convenience, the reason for the change from 62 ⁠ 1 / 2 ⁠ to 60 miles to

1938-510: A radar control facility that is associated with that specific airport. In most countries, this is referred to as terminal control and abbreviated to TMC; in the U.S., it is referred to as a 'terminal radar approach control' or TRACON. While every airport varies, terminal controllers usually handle traffic in a 30-to-50-nautical-mile (56 to 93 km; 35 to 58 mi) radius from the airport. Where there are many busy airports close together, one consolidated terminal control centre may service all

2040-428: A seamless manner; in other cases, local agreements may allow 'silent handovers', such that the receiving centre 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 its pilot begins talking to the next controller. This process continues until the aircraft is handed off to a terminal controller ('approach'). Since centres control

2142-520: 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 strips have been replaced by electronic data presented on computer screens. As new equipment

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2244-551: A surface area of about 5 nautical miles around the airport up to 1,200 ft AGL. At 1,200 ft. the airspace extends to 10 nautical miles in diameter which continues to 4,000 ft. Pilots are required to establish two-way radio communications with the ATC facility providing air traffic control service to the area before entering the airspace. Within Class ;C, Visual and Instrument pilots are separated. Class D airspace exists from

2346-447: A target by interrogating the transponder, the ADS-B equipped aircraft 'broadcasts' a position report as determined by the navigation equipment on board the aircraft. ADS-C is another mode of automatic dependent surveillance, however ADS-C operates in the 'contract' mode, where the aircraft reports a position, automatically or initiated by the pilot, based on a predetermined time interval. It

2448-415: A two or three letter combination followed by the flight number such as AAL872 or VLG1011. As such, they appear on flight plans and ATC radar labels. There are also the audio or radio-telephony call signs used on the radio contact between pilots and air traffic control. These are not always identical to their written counterparts. An example of an audio call sign would be 'Speedbird 832', instead of

2550-419: 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 related data, incorporating, in a low or high degree,

2652-541: Is a risk of confusion, usually choosing the aircraft registration identifier instead. Many technologies are used in air traffic control systems. Primary and secondary radars are used to enhance a controller's situational awareness within their 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 -equipped aircraft reply to secondary radar interrogations by giving an ID ( Mode A ), an altitude ( Mode C ), and / or

2754-416: Is a wide range of capabilities on these systems as they are being modernised. Older systems will display a map of the airport and the target. Newer systems include the capability to display higher-quality mapping, radar targets, data blocks, and safety alerts, and to interface with other systems, such as digital flight strips. Air control (known to pilots as tower or tower control ) is responsible for

2856-510: Is also coordinated with the relevant radar centre or flow control unit and ground control, to ensure that the aircraft reaches the runway in time to meet the time restriction provided by the relevant unit. At some airports, clearance delivery also plans aircraft push-backs 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 aircraft parking area gridlock. Flight data (which

2958-461: Is also possible for controllers to request more frequent reports to more quickly establish aircraft position for specific reasons. However, since the cost for each report is charged by the ADS service providers to the company operating the aircraft, more frequent reports are not commonly requested, except in emergency situations. ADS-C is significant, because it can be used where it is not possible to locate

3060-408: Is always the responsibility of the pilot in command, but air traffic controllers give instructions for sequencing and safety as needed. When a controlled flight is airborne, control passes from the tower controller who authorized the takeoff, if the airport is controlled. The next step is typically Terminal Radar Approach Control or TRACON which may be identified as "approach" or "departure". Between

3162-402: Is brought in, more and more sites are upgrading away from paper flight strips. Constrained control capacity and growing traffic lead to flight cancellation and delays : By then the market for air-traffic services was worth $ 14bn. More efficient ATC could save 5-10% of aviation fuel by avoiding holding patterns and indirect airways . The military takes 80% of Chinese airspace, congesting

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3264-519: Is no positive separation service in the airspace. This airspace roughly corresponds to the former Airport Traffic Area. Class E airspace is the airspace that lies between Classes A, B, C, and D. Class E extends from either the surface or the roof of the underlying airspace and ends at the floor of the controlled airspace above. Class E exists for those planes transitioning from the terminal to en route state. It also exists as an area for instrument pilots to remain under ATC control without flying in

3366-518: Is required to have clearance from ground control. This is normally done via VHF / UHF radio, but there may be special cases where other procedures are used. Aircraft or vehicles without radios must respond to ATC instructions via aviation light signals , or else be led by official airport 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 . Ground control

3468-480: 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

3570-438: 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 (ATIS). Many airports have

3672-619: Is the Maastricht Upper Area Control Centre (MUAC), founded in 1972 by Eurocontrol, and covering Belgium, Luxembourg, the Netherlands, and north-western Germany. In 2001, the European Union (EU) aimed to create a 'Single European Sky', hoping to boost efficiency and gain economies of scale. The primary method of controlling the immediate airport environment is visual observation from the airport control tower. The tower

3774-551: Is the area above and around the busiest airports (e.g., LAX , MIA , CVG ) and is also heavily controlled. A side view of Class B airspace resembles an upside-down wedding cake with three layers becoming bigger toward the top. Class B's layers are designed individually to meet the needs of the airport they overlay. Pilots must also receive clearance to enter the Class B airspace but Visual Flight Rules may be used, unlike in Class A airspace. Class B airspace corresponds to

3876-423: Is the most controlled airspace and requires a pilot to carry an Instrument Flight Rating and proper clearance no matter what type of aircraft is being flown. Pilots are also required to change their altimeter settings to 29.92 inHg to ensure all pilots within the airspace have the same readings in order to ensure proper altitude separation. Class B airspace extends from the surface up to 10,000 ft. AGL and

3978-606: Is the position that issues route clearances to aircraft, typically before they commence taxiing. These clearances contain details of the route that the aircraft is expected to fly after departure. Clearance delivery, or, at busy airports, ground movement planner (GMP) or traffic management coordinator (TMC) will, if necessary, coordinate with the relevant radar centre or flow control unit to obtain releases for aircraft. At busy airports, these releases are often automatic, and are controlled by local agreements allowing 'free-flow' departures. When weather or extremely high demand for

4080-413: Is typically a tall, windowed structure, located within the airport grounds. The air traffic controllers , usually abbreviated 'controller', are responsible for separation and efficient movement of aircraft and vehicles operating on the taxiways and runways of the airport itself, and aircraft in the air near the airport, generally 5 to 10 nautical miles (9 to 19 kilometres ; 6 to 12 miles ), depending on

4182-584: Is uncontrolled airspace which extends from the surface to either 700 or 1,200 ft. AGL depending on the floor of the overlying Class E, or to the floor of Class A where there is no overlying Class E. In the vicinity of an uncontrolled airport, the CTAF for that airport is used for radio communication among pilots. In remote areas other frequencies such as MULTICOM are used. No towers or in-flight control services are provided although communications may be established with flight service stations which are not part of

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4284-480: Is very near to 21,600 nautical miles (that is 60 minutes × 360 degrees). Today the international nautical mile is defined as 1,852 metres (about 6,076 ft; 1.151 mi). The derived unit of speed is the knot , one nautical mile per hour. There is no single internationally agreed symbol, with several symbols in use. The word mile is from the Latin phrase for a thousand paces: mille passus . Navigation at sea

4386-466: 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 , 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

4488-762: The Federal Aviation Administration to the airline industry. The National Business Aviation Association (NBAA), the General Aviation Manufacturers Association, the Aircraft Owners and 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

4590-562: The U.S. Army to direct and track the movements of reconnaissance aircraft . Over time, the AMRS morphed into flight service stations . Today's flight service stations do not issue control instructions, but provide pilots with many other flight related informational services. They do relay control instructions from ATC in areas where flight service is the only facility with radio or phone coverage. The first airport traffic control tower, regulating arrivals, departures, and surface movement of aircraft in

4692-528: The EU called for a 'Digital European Sky', focusing on cutting costs by including a common digitisation standard, and allowing controllers to move to where they are needed instead of merging national ATCs, as it would not solve all problems. Single air-traffic control services in continent-sized America and China does not alleviate congestion. Eurocontrol tries to reduce delays by diverting flights to less busy routes: flight paths across Europe were redesigned to accommodate

4794-433: The NAS and advisory service may be available from ARTCC. Airport tower#Airport control Air traffic control ( ATC ) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace , and can provide advisory services to aircraft in non-controlled airspace. The primary purpose of ATC is to prevent collisions, organize and expedite

4896-457: The NAS is transitioning to a new system known as NextGen , which applies non-radar surveillance of aircraft equipped with GPS satellite-based navigation systems continuously reporting their location. Aircraft also receive the broadcast location of others nearby, which improves safety. The system also allows pilots to use more precise and efficient landing paths, saving time and fuel. NextGen is being phased in piece by piece. In June 2018, NASA flew

4998-407: The U.S. airspace is covered by radar, and often by multiple radar systems; however, coverage may be inconsistent at lower altitudes used by aircraft, due to high terrain or distance from radar facilities. A centre 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

5100-485: The U.S., TRACONs are additionally designated by a three-digit alphanumeric code. For example, the Chicago TRACON is designated C90. Air traffic control also provides services to aircraft in flight between airports. Pilots fly under one of two sets of rules for separation: visual flight rules (VFR), or instrument flight rules (IFR). Air traffic controllers have different responsibilities to aircraft operating under

5202-573: The US at a specific airport, opened in Cleveland in 1930. Approach / departure control facilities were created after adoption of radar in the 1950s to monitor and control the busy airspace around larger airports. The first air route traffic control center (ARTCC), which directs the movement of aircraft between departure and destination, was opened in Newark in 1935, followed in 1936 by Chicago and Cleveland. Currently in

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5304-533: The US, the Federal Aviation Administration (FAA) operates 22 Air Route Traffic Control Centers . After the 1956 Grand Canyon mid-air collision , killing all 128 on board, the FAA was given the air-traffic responsibility in the United States in 1958, and this was followed by other countries. In 1960, Britain, France, Germany, and the Benelux countries set up Eurocontrol , intending to merge their airspaces. The first and only attempt to pool controllers between countries

5406-465: The active runway surfaces. Air control gives clearance for aircraft takeoff or landing, whilst ensuring that prescribed runway separation will exist at all times. If the air controller detects any unsafe conditions, a landing aircraft may be instructed to ' go-around ', and be re-sequenced into the landing pattern. This re-sequencing will depend on the type of flight, and may be handled by the air controller, approach, or terminal area controller. Within

5508-471: The air by holding 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 aircraft hours in advance. Thus, aircraft 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

5610-419: The air controllers aware of the traffic flow towards their runways to maximise runway utilisation through effective approach spacing. Crew resource management (CRM) procedures are often used to ensure this communication process is efficient and clear. Within ATC, it is usually known as 'team resource management' (TRM), and the level of focus on TRM varies within different ATC organisations. Clearance delivery

5712-900: The air traffic control system are primarily related to the volume of air traffic demand placed on the system, and weather. 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 , before the next aircraft 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 aircraft arrivals per hour. A large airport with two arrival runways can handle about 60 arrivals per hour in good weather. Problems arise when airlines 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

5814-454: The air, a ground delay programme may be established, delaying aircraft on the ground before departure due to conditions at the arrival airport. In Area Control Centres, a major weather problem is thunderstorms , which present a variety of hazards to aircraft. Airborne 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

5916-412: The aircraft approaches its destination, the centre is responsible for issuing instructions to pilots so that they will meet 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

6018-481: The aircraft operator, and identical call sign might 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 east-bound, and odd if west-bound. In order to reduce the possibility of two call signs on one frequency at any time sounding too similar,

6120-557: The aircraft. Pursuant to requirements of the International Civil Aviation Organization (ICAO), ATC operations are conducted either in the English language, or the local language used by the station on the ground. In practice, the native language for a region is used; however, English must be used upon request. In 1920, Croydon Airport near London, England, was the first airport in the world to introduce air traffic control. The 'aerodrome control tower'

6222-424: The airport procedures. A controller must carry out the job using the precise and effective application of rules and procedures; however, they need flexible adjustments according to differing circumstances, often under time pressure. In a study that compared stress in the general population and this kind of system markedly showed more stress level for controllers. This variation can be explained, at least in part, by

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6324-711: The airport. Some airports have no TRACON around them, so control goes directly to or from a Center, and some flights are low enough and short enough that control is kept within one or more TRACONs without ever being passed to Center. Approximately 14,500 air traffic controllers, 4,500 aviation safety inspectors, and 5,800 technicians operate and maintain services for the NAS. It has more than 19,000 airports and 600 air traffic control facilities. In all, there are 41,000 NAS operational facilities. In addition, there are over 71,000 pieces of equipment, ranging from radar systems to communication relay stations. On average, about 45,000 flights use NAS services each day. As of February 2015

6426-527: The airports. The airspace boundaries and altitudes assigned to a terminal control centre, which vary widely from airport to airport, are based on factors such as traffic flows, neighbouring airports, and terrain. A large and complex example was the London Terminal Control Centre (LTCC), which controlled traffic for five main London airports up to an altitude of 20,000 feet (6,096 metres) and out to

6528-564: 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

6630-427: The area formerly known as a Terminal Control Area or TCA. Class C airspace reaches from the surface to 4,000 ft. AGL above the airport which it surrounds. Class C airspace only exists over airports which have an operational control tower, are serviced by a radar approach control, and have a certain number of instrument flight operations. Class C is also individually designed for airports but usually covers

6732-470: 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 Flightradar24 , FlightExplorer, FlightView, and FlyteComm. Each company maintains a website that provides free updated information to the public on flight status. Stand-alone programmes are also available for displaying

6834-528: The centre provides a clearance. Centre controllers are responsible for issuing instructions to pilots to climb their aircraft to their assigned altitude, while, at the same time, ensuring that the aircraft is properly separated from all other aircraft in its 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

6936-502: The characteristics of the job. Surveillance displays are also available to controllers at larger airports to assist with controlling air traffic. Controllers may use a radar system called secondary surveillance radar 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, altitude, and other information described in local procedures. In adverse weather conditions,

7038-590: The controller further: In the United States, some alterations to traffic control procedures are being examined: In Europe, the Single European Sky ATM Research (SESAR) programme plans to develop new methods, technologies, procedures, and systems to accommodate future (2020 and beyond) air traffic needs. In October 2018, European controller unions dismissed setting targets to improve ATC as "a waste of time and effort", as new technology could cut costs for users but threaten their jobs. In April 2019,

7140-472: The different sets of rules. While IFR flights are under positive control, in the US and Canada, VFR pilots can request 'flight following' (radar advisories), which provides traffic advisory services on a time permitting basis, and may also provide assistance in avoiding areas of weather and flight restrictions, as well as allowing pilots into the air traffic control system prior to the need to a clearance into certain airspace. Throughout Europe, pilots may request

7242-598: The equivalent term air route traffic control center. Each centre is responsible for a given flight information region (FIR). Each flight information region typically covers many thousands of square miles of airspace, and the airports within that airspace. Centres 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. Centres may also 'pick up' VFR aircraft that are already airborne, and integrate them into their system. These aircraft must continue under VFR flight rules until

7344-565: The flow of traffic in the air, and provide information and other support for pilots. Personnel of air traffic control monitor aircraft location in their assigned airspace by radar , and communicate with the pilots by radio . To prevent collisions, ATC enforces traffic separation rules, which ensure each aircraft maintains a minimum amount of 'empty space' around it at all times. It is also common for ATC to provide services to all private , military , and commercial aircraft operating within its airspace; not just civilian aircraft. Depending on

7446-523: The following provides a general concept of the delegation of responsibilities within the air traffic control tower environment. Remote and virtual tower (RVT) is a system based on air traffic controllers being located somewhere other than at the local airport tower, and still able to provide air traffic control services. Displays for the air traffic controllers may be live video, synthetic images based on surveillance sensor data, or both. Ground control (sometimes known as ground movement control , GMC)

7548-432: The geographic location of airborne instrument flight rules (IFR) air traffic anywhere in the FAA air traffic system. Positions are reported for both commercial and general aviation traffic. The programmes can overlay air traffic with a wide selection of maps such as, geo-political boundaries, air traffic control centre boundaries, high altitude jet routes, satellite cloud and radar imagery. The day-to-day problems faced by

7650-427: 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. En-route air traffic controllers work in facilities called air traffic control centres, each of which is commonly referred to as a 'centre'. The United States uses

7752-408: 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 systems , making it available to controllers. The Federal Aviation Administration (FAA) has spent over US$ 3 billion on software, but a fully automated system is still yet to be achieved. In 2002, the United Kingdom commissioned

7854-559: The infrastructure for a radar system (e.g., over water). Computerised radar displays are now being designed to accept ADS-C inputs as part of their 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' (PAR) are commonly used by military controllers of air forces of several countries, to assist

7956-547: The international nautical mile was defined by the First International Extraordinary Hydrographic Conference in Monaco as exactly 1,852 metres (which is 6,076.12 ft). The United States did not adopt the international nautical mile until 1954. Britain adopted it in 1970, but legal references to the obsolete unit are now converted to 1,853 metres (which is 6,079.40 ft). The metre

8058-424: The last three numbers (e.g. three-four-five for N12345). In the United States, the prefix may be an aircraft type, model, or manufacturer in place of the first registration character, for example, 'N11842' could become 'Cessna 842'. This abbreviation is only allowed after communications have been established in each sector. Before around 1980, International Air Transport Association (IATA) and ICAO were using

8160-430: The measurement based on this ( ⁠ 40,075.017 km / 360 × 60 ⁠ = 1,855.3 metres) is known as the geographical mile . Using the definition ⁠ 1 / 60 ⁠ of a degree of latitude on Mars , a Martian nautical mile equals to 983 m (1,075 yd). This is potentially useful for celestial navigation on a human mission to the planet , both as a shorthand and a quick way to roughly determine

8262-521: The new airport in Istanbul, which opened in April, but the extra capacity will be absorbed by rising demand for air travel. Well-paid jobs in western Europe could move east with cheaper labour. The average Spanish controller earn over €200,000 a year, over seven times the country average salary, more than pilots, and at least ten controllers were paid over €810,000 ($ 1.1m) a year in 2010. French controllers spent

8364-438: The overall capacity for any given route. The North Atlantic Track system is a notable example of this method. Some air navigation service providers (e.g., Airservices Australia, the U.S. Federal Aviation Administration, Nav Canada , etc.) have implemented automatic dependent surveillance – broadcast (ADS-B) as part of their surveillance capability. This newer technology reverses the radar concept. Instead of radar 'finding'

8466-482: The pilot in final phases of landing in places where instrument landing system and other sophisticated airborne equipment are unavailable to assist the pilots in marginal or near zero visibility conditions. This procedure is also called a 'talk-down'. 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,

8568-453: The poles and 1,843 metres at the Equator. France and other metric countries state that in principle a nautical mile is an arcminute of a meridian at a latitude of 45°, but that is a modern justification for a more mundane calculation that was developed a century earlier. By the mid-19th century, France had defined a nautical mile via the original 1791 definition of the metre , one ten-millionth of

8670-544: The presence of traffic and conditions that lead to loss of minimum separation. Beyond runway capacity issues, the weather is a major factor in traffic capacity. Rain, ice , snow, or hail 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 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

8772-400: The same destination so that when the aircraft are close to their destination they are sequenced. As an aircraft reaches the boundary of a centre's control area, it is 'handed off' or 'handed over' to the next area control centre . 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

8874-542: The same two-letter call signs. Due to the larger number of new airlines after deregulation, the ICAO established the three-letter call signs as mentioned above. The IATA call signs are currently used in aerodromes on the announcement tables, but are no longer used in air traffic control. For example, AA is the IATA call sign for American Airlines ; the ATC equivalent is AAL. Flight numbers in regular commercial flights are designated by

8976-456: The sectors administered by TRACONs are 20 contiguous areas of US airspace above 18,000 feet, each managed by an Air Route Traffic Control Center (ARTCC) typically referred to on the radio as "Center". A flight is handed off from one Center to another until it descends near its destination, when control is transferred to the TRACON serving the destination, and ultimately to the tower controller serving

9078-451: The surface to 2,500 ft. AGL above an airport. Class D airspace only surrounds airports with an operational control tower. Class D airspace is also tailored to meet the needs of the airport. Pilots are required to establish and maintain two-way radio communications with the ATC facility providing air traffic control services prior to entering the airspace. Pilots using Visual Flight Reference must be vigilant for traffic as there

9180-418: The thin corridors open to airliners. The United Kingdom closes its military airspace only during military exercises. 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 and other military services for military flights . There are written call signs with

9282-728: The tower controllers may also use surface movement radar (SMR), surface movement guidance and control system (SMGCS), or advanced surface movement guidance and control system (ASMGCS) to control traffic on the manoeuvring area (taxiways and runways). The areas of responsibility for tower controllers fall into three general operational disciplines: local control or air control, ground control, and flight data / clearance delivery. Other categories, such as airport apron control, or ground movement planner, may also exist at extremely busy airports. While each tower may have unique airport-specific procedures, such as multiple teams of controllers ( crews ) at major or complex airports with multiple runways,

9384-452: 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 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 service either all the time, or for any periods of radar outage for any reason. In

9486-432: The tower, a highly disciplined communications process between the air control and ground control is an absolute necessity. Air 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 gaps in the arrival traffic; to allow taxiing traffic to cross runways, and to allow departing aircraft to take off. Ground control needs to keep

9588-425: The type of flight and the class of airspace, ATC may issue instructions that pilots are required to obey, or advisories (known as flight information in some countries) that pilots may, at their discretion, disregard. The pilot in command of an aircraft always retains final authority for its safe operation, and may, in an emergency, deviate from ATC instructions to the extent required to maintain safe operation of

9690-557: The world's ocean areas. These areas are also flight information regions (FIRs). Because there are no radar systems available for oceanic control, oceanic controllers provide ATC services using procedural control . These procedures use aircraft position reports, time, altitude, distance, and speed, to ensure separation. Controllers record information on flight progress strips , and in specially developed oceanic computer systems, as aircraft report positions. This process requires that aircraft be separated by greater distances, which reduces

9792-492: The written 'BAW832'. This is used to reduce the chance of confusion between ATC and the aircraft. By default, the call sign for any other flight is the registration number (or tail number in US parlance) of the aircraft, such as 'N12345', 'C-GABC', or 'EC-IZD'. The short radio-telephony call signs for these tail numbers is the last three letters using the NATO phonetic alphabet (e.g. ABC, spoken alpha-bravo-charlie for C-GABC), or

9894-466: Was 60 miles per degree. However, these referred to the old English mile of 5000 feet and league of 15,000 feet, relying upon Ptolemy's underestimate of the Earth's circumference . In the early seventeenth century, English geographers started to acknowledge the discrepancy between the angular measurement of a degree of latitude and the linear measurement of miles. In 1624 Edmund Gunter suggested 352,000 feet to

9996-497: Was a sphere. In 1574, William Bourne stated in A Regiment for the Sea the "rule to raise a degree" practised by navigators: "But as I take it, we in England should allowe 60 myles to one degrée: that is, after 3 miles to one of our Englishe leagues, wherefore 20 of oure English leagues shoulde answere to one degrée." Likewise, Robert Hues wrote in 1594 that the distance along a great circle

10098-414: Was a wooden hut 15 feet (5 metres) high with windows on all four sides. It was commissioned on 25 February 1920, and provided basic traffic, weather, and location information to pilots. In the United States, air traffic control developed three divisions. The first of several air mail radio stations (AMRS) was created in 1922, after World War I, when the U.S. Post Office began using techniques developed by

10200-451: Was done by eye until around 1500 when navigational instruments were developed and cartographers began using a coordinate system with parallels of latitude and meridians of longitude . The earliest reference of 60 miles to a degree is a map by Nicolaus Germanus in a 1482 edition of Ptolemy 's Geography indicating one degree of longitude at the Equator contains " milaria 60 ". An earlier manuscript map by Nicolaus Germanus in

10302-487: Was originally defined as 1 ⁄ 10,000,000 of the length of the meridian arc from the North pole to the equator (1% of a centesimal degree of latitude), thus one kilometre of distance corresponds to one centigrad (also known as centesimal arc minute) of latitude. The Earth's circumference is therefore approximately 40,000 km. The equatorial circumference is slightly longer than the polar circumference –

10404-449: Was revised with better estimates of the earth’s circumference. In 1637, Robert Norwood proposed a new measurement of 6120 feet for an arcminute of latitude, which was within 44 feet of the currently accepted value for a nautical mile. Since the Earth is not a perfect sphere but is an oblate spheroid with slightly flattened poles, a minute of latitude is not constant, but about 1,862 metres at

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