A terminal radar approach control (or TRACON) is an air traffic control facility usually located within the vicinity of a large airport. Typically, the TRACON controls aircraft within a 20-50 nautical mile (37 to 93 km) radius of the major airport and a number of "satellite airports" between surface and 1,200 feet (370 m) up to between 10,000 feet (3,000 m) and 23,000 feet (7,000 m). A TRACON is sometimes called approach control or departure control in radio transmissions. In the US Air Force it is known as RAPCON (Radar Approach Control), and in the US Navy as a "RATCF" (Radar Air Traffic Control Facility) In Canada, Approach Control may be called arrival or terminal. TRACONs operate in US FAA Class A, B, C, and D airspaces. In class A spaces TRACONs perform transitions of aircraft radio contact to and from the en-route center.
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TRACONs normally have their own radar system that allow air traffic controllers to track aircraft. This is typically based on one or more Airport Surveillance Radar(s) (ASR), sweeping once every 4-5 seconds. The busiest TRACON in the world (Southern California TRACON - SCT, Callsign SoCal Approach) services 62 airports and is located in San Diego, California. This huge facility utilizes 11 radar sites. Most US terminal Radar Approach Control (TRACON) facilities utilize an ASR-9 with a range of 63 7/8 miles (103 km) and a scan rate (rotation) of approximately 4.5 seconds.
These frequent updates help controllers see the result of direction changes quickly. Larger U.S. TRACONs are able to directly incorporate en route long range Air Route Surveillance Radar(s) (ARSR) into their automated tracking systems as a backup. Smaller U.S. TRACONs also have the capability to make use of CENRAP (CENter RAdar Presentation) as a backup if their primary system fails. This makes use of en-route surveillance radar used by Air Route Traffic Control Centers (ARTCCs). Expanded separation minimums (5 nautical miles (9.3 km) versus 3 nautical miles) are required when in this mode.
Most of the United States FAA TRACONs are currently using Common ARTS equipment. Most of ARTS IIIA and some ARTS IIE sites have been updated to Raytheon's Standard Terminal Automation Replacement System (STARS) equipment. The program to manage the updates is now called Terminal Automation Modernization/Replacement (TAMR). In the Spring of 2011, it was announced by the FAA that all remaining ARTS equipment will be replaced with STARS equipment. The 11 largest TRACONS will be done first as part of TAMR Segment 3 Phase 1. The fate of the remaining ARTS IIE sites has not been announced by the FAA as of Summer 2011. This program, when announced, will be titled as TAMR Segment 3 Phase 2.
TRACON control positions usually include a radar controller and a coordinator who generally stands behind the radar position.
The radar controller is responsible for ensuring appropriate separation, and issuing traffic and other local aviation information for aircraft under its control. Additionally, the radar controller is responsible for ensuring all required coordination with other controllers in the tower, TRACON, or en-route center is completed, making required computer entries, and updating the flight progress strips.
The coordinator provides coordination support for the radar controller. He/she will provide inter/intra facility coordination when required for the radar controller and make computer entries.
Some TRACONs have the ability to staff a second position at the radar console, referred to as a "Assistant" or "D Side" (FAA) controller. This position is responsible for providing direct support by coordinating for the radar controller, managing flight progress strips, and making computer entries. When this position is staffed, the coordinator duties are greatly reduced, allowing him/her to provide support for a number of positions. The support controller may make transmissions on the radio along with the main controller: the support controller focuses on the more procedural aspects of controlling (e.g. holding aircraft) while the main controller focuses on accurately radar-vectoring the approach sequence.
TRACONs are responsible for providing all ATC services within their airspace. Generally, there are four types of traffic flows controlled by TRACON controllers. These are departures, arrivals, overflights, and aircraft operating under Visual Flight Rules (VFR).
Departure aircraft are received from the control tower from which the aircraft departs and are generally 1,000 feet (300 m) to 2,000 feet (610 m) high, climbing to a pre-determined altitude. The TRACON controller working this traffic is responsible for clearing all other TRACON traffic and, based on the route of flight, placing the departing aircraft on a track and in a geographical location (sometimes referred to as a "gate" or "exit") that is set through agreements with the en-route center. This positioning is designed to allow the en-route center to integrate the aircraft into its traffic flow easily.
Arrival aircraft other than Visual Flight Rules aircraft entering the area are received from the en-route center in compliance with pre-determined agreements on routing, altitude, speed, spacing, etc. The TRACON controller working this traffic will take control of the aircraft and blend it with other aircraft entering the center airspace from other areas or "gates" into a single, parallel or perpendicular final for a runway at any of the airports with the TRACON space. The spacing is critical to ensure the aircraft can land and clear the runway prior to the next aircraft touching down on the runway. The TRACON controller will do a hand-off to pass the flight communication to the approach airport tower. That tower controller may also request expanded spacing between aircraft to allow aircraft to depart or to cross the runway in use.
Overflight aircraft are aircraft that enter the TRACON airspace at one point and exit the airspace at another without landing at an airport. They must be controlled in a manner that ensures they remain separated from the climbing and descending traffic that is moving in and out of the airport. Their route may be altered to ensure this is possible. When they are returned to the en-route center, they must be on the original routing unless a change has been coordinated.
If the class of airspace allows flight under VFR, such aircraft are handled as traffic permits. Controllers will provide traffic information to ensure safety with other aircraft, and may even positively separate VFR aircraft from other aircraft, depending on the class of airspace. Controllers spend extra time with these flights in order to avoid vectoring VFR aircraft into IMC. Controllers usually provide information for the pilot about traffic in the immediate vicinity and weather information. This ensures that separation from Instrument Flight Plan (IFR) aircraft is maintained within the controller's coverage area.
Most US airports do not have a TRACON available. In this case, the en-route center will coordinate directly with the tower and provide this type of service where radar coverage permits. In these cases, the separation minimums are greatly increased. In many countries, mid-sized airports without a TRACON have a dedicated Approach Radar Controller based upon the airport itself to sequence inbound flights and to provide radar services to aircraft in the vicinity of the airport.