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100-590: The positions of the aircraft are displayed on a screen; at large airports on multiple screens in an operations room at the airport called in the US the Terminal Radar Approach Control (TRACON), monitored by air traffic controllers who direct the traffic by communicating with the aircraft pilots by radio. They are responsible for maintaining a safe and orderly flow of traffic and adequate aircraft separation to prevent midair collisions . Radar

200-418: A transponder . The secondary radar is a rotating flat antenna, often mounted on top of the primary radar dish, which transmits a narrow vertical fan-shaped microwave beam on a frequency of 1030 MHz in the L band with peak power of 160 - 1500 W. When it is interrogated by this signal, the aircraft's transponder beacon transmits a coded identifying microwave signal at a frequency of 1090 MHz back to

300-477: 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

400-451: 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 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

500-512: A 60 nautical mile radius. ASR 8 used a klystron as transmitters power amplifier stage with a load of 79 kV and 40A. The two operational frequencies have a minimum separation of 60 MHz. The US Army/Navy designator AN/GPN-20 refers to a modified version of the ASR 8 used by the USAF containing a magnetron tube as transmitter. To improve the magnetron's frequency stability the magnetron tuning

600-400: 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

700-433: 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

800-416: 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

900-493: A cumulative nine months on strike between 2004 and 2016. Mode C veil Mode C veil refers to a kind of airspace which currently surrounds all primary Class B airports within the United States . This airspace extends horizontally to a circle of 30  NM radius centered on the airport, and extends vertically from the surface up to 10,000 feet MSL . The name refers to the mode of transponder operation which

1000-400: 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

1100-432: 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

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1200-414: 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

1300-417: 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, 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

1400-401: A mode C transponder which can report altitude, due to their strict requirements for aircraft altitude spacing; this is called a " Mode C veil ". Due to its crucial safety purpose, extreme uptime requirements, and need to be compatible with all the different types of aircraft and avionics systems, the design of airport surveillance radar is strictly controlled by government agencies. In the US

1500-746: 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

1600-472: 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

1700-400: A peak power of 1.3 MW and a pulse duration of 1 μs and pulse repetition frequency between 325 and 1200 pps. It can be switched to a second reserve frequency if interference is encountered on the primary frequency. The receiver has the sensitivity to detect a radar cross-section of 1 meter at 111 km, and a range resolution of 450 feet. The antenna covers an elevation of 40° from

1800-510: 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

1900-403: A rate of 12.5 RPM so the airspace is scanned every 4.8 seconds. The electronics is dual-channel and fault tolerant. It has a remote monitoring and maintenance subsystem; if a fault occurs a built-in test detects and isolates the problem. Like all airport surveillance radars it has a backup diesel generator to continue operating during power outages. The Digital Airport Surveillance Radar (DASR)

2000-428: 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

2100-523: A secondary radar system developed from the limitations of primary radar and need for more information by air traffic controllers due to the increasing postwar volume of air traffic. The primary radar displays a "return" indiscriminately from any object in its field of view, and cannot distinguish between aircraft, drones, weather balloons, birds, and some elevated features of the terrain (called " ground clutter "). Primary radar also cannot identify an aircraft; before secondary radar aircraft were identified by

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2200-531: A short range radar, or once every 12–13 seconds for a slower rotating long range radar. The FAA is mandating that ADS-B be fully operational and available to the NAS by the year 2020. This will make possible the decommissioning of older radars in order to increase safety and cut costs. As of 2011, there is no definitive list of radars that will be decommissioned as a result of ADS-B implementation. Terminal Radar Approach Control Air traffic control ( ATC )

2300-520: 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

2400-480: 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 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

2500-451: 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

2600-415: 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

2700-419: 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,

2800-541: 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

2900-508: 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 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

3000-416: 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

3100-510: 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

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3200-464: 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

3300-402: 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

3400-538: Is driven by the AFC. The current generation of radar is the ASR-9 , which was developed by Westinghouse Electric Corporation and first installed in 1989, with installation completing in 1995. The military nomenclature for the radar is AN/GPN-27. Currently it is operating at 135 locations and is scheduled to continue in use until at least 2025. The ASR-9 was the first airport surveillance radar to detect weather and aircraft with

3500-518: 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

3600-514: Is required within this airspace — that is, with very limited exceptions, all aircraft operating within this airspace must have an altitude-reporting Mode C transponder in operation. An additional requirement for the transponder to have ADS-B Out became effective January 1, 2020. As of August 2017 , all 37 Class B airports in the United States have Mode C veils centered on them. Prior to November 2014, two Class B airports did not have

3700-480: 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

3800-438: 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

3900-557: Is the new generation of fully digital radar that is being developed to replace the current analog systems. The US Air Force Electronics Systems Center, the US Federal Aviation Administration , US Army and the US Navy procured DASR systems to upgrade existing radar facilities for US Department of Defense (DoD) and civilian airfields. The DASR system detects aircraft position and weather conditions in

4000-498: Is the only facility with radio or phone coverage. The first airport traffic control tower, regulating arrivals, departures, and surface movement of aircraft in the US at a specific airport, opened in Cleveland in 1930. Approach / 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

4100-606: 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

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4200-434: Is used by controllers, at all terminal radar facilities in the US to provide air traffic control (ATC) services to aircraft in the terminal areas. Typical terminal area ATC services are defined as the area around airports where departing and arriving traffic are served. Functions include aircraft separation, weather advisories, and lower level control of air traffic. The system is designed to accommodate air traffic growth and

4300-466: 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

4400-510: The Federal Aviation Administration (FAA) is responsible for developing airport surveillance radar. All ASRs have the common requirements of detecting aircraft out to a range of 60 miles and an elevation of 25,000 feet. Upgrades are released in "generations" after careful testing: This is an obsolete system that is completely out of service. ASR 8 is the analog precursor to the ASR 9. The military nomenclature for

4500-817: 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

4600-400: The S band with a peak radiated power of 25 kW and an average power of 2.1 kW. The dish is rotated at a constant rate about a vertical axis so the beam scans the entire surrounding airspace about every 5 seconds. When the microwave beam strikes an airborne object, the microwaves are reflected and some of the energy (sometimes called the "echo") returns to the dish and is detected by

4700-733: 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 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

4800-641: The DASR system. ASR data is displayed on Standard Terminal Automation Replacement System (STARS) display consoles in control towers and Terminal Radar Approach Control (TRACON) rooms, usually located at airports. The Standard Terminal Automation Replacement System (STARS) is a joint Federal Aviation Administration (FAA) and Department of Defense (DoD) program that has replaced Automated Radar Terminal Systems (ARTS) and other capacity-constrained, older technology systems at 172 FAA and up to 199 DoD terminal radar approach control facilities and associated towers. STARS

4900-531: 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

5000-407: 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

5100-492: 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

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5200-465: 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

5300-471: 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

5400-468: 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

5500-900: 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

5600-454: 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

5700-412: 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

5800-481: 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,

5900-412: The airport called in the US the Terminal Radar Approach Control (TRACON). The primary radar's main function is to determine the location, the bearing and range to the aircraft. Air traffic controllers continuously monitor the positions of all the aircraft on the radar screen, and give directions to the pilots by radio to maintain a safe and orderly flow of air traffic in the airspace. The need for

6000-543: 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

6100-578: 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

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6200-470: 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

6300-528: 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

6400-535: The controller asking the aircraft by radio to turn onto a specified heading. Another limitation is that primary radar cannot determine the altitude of the aircraft. Secondary surveillance radar (SSR), also called the air traffic control radar beacon system (ATCRBS) had its origin in Identification Friend or Foe (IFF) systems used by military aircraft during World War II. All aircraft are required to carry an automated microwave transceiver called

6500-603: 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,

6600-472: 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

6700-598: 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

6800-575: The extent required to maintain safe operation of 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,

6900-523: 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)

7000-432: 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

7100-427: 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

7200-403: The horizon with two feedhorns which create two stacked overlapping vertical lobes 4° apart; the lower beam transmits the outgoing pulse and is used to detect distant targets near the horizon, while the upper receive-only beam detects closer higher elevation aircraft with less ground clutter. The antenna has a gain of 34 dB, beamwidth of 5° in elevation and 1.4° in azimuth . It rotates at

7300-408: 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

7400-571: 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

7500-640: The introduction of new automation functions which will improve the safety and efficiency of the US National Airspace System (NAS). Airport Surveillance Radar is beginning to be supplemented by ADS-B Automatic dependent surveillance-broadcast in the US and other parts of the world. As of Spring 2011, ADS-B is currently operational at most ATC facilities in the US. ADS-B is a GPS based technology that allows aircraft to transmit their GPS determined position to display systems as often as once per second, as opposed to once every 5–6 seconds for

7600-424: 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

7700-517: 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,

7800-465: The movement of aircraft between departure and destination, was opened in Newark in 1935, followed in 1936 by Chicago and Cleveland. Currently in 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

7900-530: 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

8000-438: 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'

8100-482: 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,

8200-544: 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

8300-493: The radar is AN/GPN-20. It is an aging radar system that is obsolete, not logistically supported, does not provide digital inputs to new terminal automation systems, and does not provide a calibrated precipitation intensity product nor any storm motion information. It is a relocatable, solid-state, all-weather radar with dual-channel, frequency diversity, remote operator controls, and a dual beam tower mounted antenna. The radar provides controllers with range azimuth of aircraft within

8400-467: The radar receiver. Since the microwaves travel at a constant speed very close to the speed of light , by timing the brief interval between the transmitted pulse and the returning "echo" the radar can calculate the range from the antenna to the object. The location of the object is displayed as an icon on a map display called a "radar screen". The screen may be located in the control tower , or at large airports on multiple screens in an operations room at

8500-502: The same beam and be able to display them on the same screen. It has a digital Moving Target Detection (MTD) processor which uses doppler radar and a clutter map giving advanced ability to eliminate ground and weather clutter and track targets. It is theoretically capable of tracking a maximum of 700 aircraft simultaneously. The klystron tube transmitter operates in the S-band between 2.5 and 2.9 GHz in circular polarization with

8600-400: 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

8700-550: 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

8800-432: The secondary radar antenna. This coded signal includes a 4 digit number called the "transponder code" which identifies the aircraft, and the aircraft's pressure altitude from the pilot's altimeter . This information is displayed on the radar screen beside the aircraft's icon for use by the air traffic controller. The transponder code is assigned to the aircraft by the air traffic controller before takeoff. Controllers use

8900-418: 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 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

9000-428: The term "squawk" when they are assigning a transponder code, e.g., "Squawk 7421". Transponders can respond with one of several different "modes" determined by the interrogation pulse from the radar. Various modes exist from Mode 1 to 5 for military use, to Mode A, B, C and D, and Mode S for civilian use. Only Mode C transponders report altitude. Busy airports usually require all aircraft entering their airspace to have

9100-418: 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

9200-452: 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

9300-432: 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

9400-519: The vicinity of civilian and military airfields. The civilian nomenclature for this radar is ASR-11 . The ASR-11 will replace most ASR-7 and some ASR-8. The military nomenclature for the radar is AN/GPN-30. The older radars, some up to 20 years old, are being replaced to improve reliability, provide additional weather data, reduce maintenance cost, improve performance, and provide digital data to new digital automation systems for presentation on air traffic control displays. The Iraqi Air Force has received

9500-557: 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

9600-496: 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

9700-507: Was created in 1922, after World War I, when the U.S. Post Office began using techniques developed by the U.S. Army to direct and track the movements of reconnaissance aircraft . Over time, the AMRS morphed into flight service stations . Today's flight service stations do not issue control instructions, but provide pilots with many other flight related informational services. They do relay control instructions from ATC in areas where flight service

9800-409: Was developed during World War II as a military air defense system. The primary surveillance radar (PSR) consists of a large parabolic "dish" antenna mounted on a tower so it can scan the entire airspace unobstructed. It transmits pulses of microwave radio waves in a narrow vertical fan-shaped beam about a degree wide. In the US the primary radar operates at a frequency of 2.7 - 2.9 GHz in

9900-702: Was followed by other countries. In 1960, Britain, France, Germany, and the Benelux countries set up Eurocontrol , intending to merge their airspaces. The first and only attempt to pool controllers between countries is the Maastricht Upper Area Control Centre (MUAC), founded in 1972 by Eurocontrol, and covering Belgium, Luxembourg, the Netherlands, and north-western Germany. In 2001, the European Union (EU) aimed to create

10000-415: Was the first airport in the world to introduce air traffic control. The 'aerodrome control tower' 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)

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