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The Basics
Air traffic control (ATC) depends on an electronic triad of communications, surveillance, and navigation. ATC uses radio and radar in conjunction with ground-based navigational aids to control the flow of air traffic. Communication with aircraft is handled primarily by airport traffic control towers (ATCTs), air route traffic control centers (ARTCCs or centers), and flight service stations (FSSs).
Control Towers
 Airport control towers provide for the safe, orderly, and expeditious flow of traffic on and in the vicinity of airports. They sometimes also provide for the separation of instrument flight rules (IFR) aircraft in terminal areas through co-located terminal radar approach control (TRACON) facilities. Some control towers are not staffed by Federal Aviation Administration (FAA) employees but are operated by private firms. These nonfederal control towers (NFCTs) are nevertheless staffed by FAA certificated air traffic controllers.
There are more than 260 FAA airport control towers in the United States. More than 220 federal contract towers and 164 military towers also help separate aircraft. There are also 21 terminal radar approach facilities (TRACONs), some of which are collocated with airport control towers.
Airport Surveillance Radar (ASR)
Airport surveillance radar (ASR) provides relatively short-range coverage within about 40 miles of an airport and assists "approach control" in handling terminal traffic. It also can be used as an instrument approach aid. In addition, precision approach radar (PAR) is available at some locations to allow controllers to guide an airplane to a landing under instrument weather conditions in place of on-board approach navigation equipment.
Air Route Surveillance Radar (ARSR)
Air route surveillance radar (ARSR) is a system of remotely located, long-range radars that primarily provides a display of aircraft locations over large areas to air route traffic control centers (ARTCCs or centers).
Flight Service Stations
 Flight service stations (FSS) provide pilot weather briefings. They also handle en route communications and initiate search and rescue procedures for overdue aircraft operating under visual flight rules (VFR). They assist lost aircraft and aircraft in emergency situations; relay ATC clearances; broadcast weather and airspace information; receive and process flight plans; and monitor navigational aids. There are 74 flight service stations in the United States.
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Radar
 Radar is air traffic control's (ATC's) primary surveillance system, comprising airport surveillance radar (ASR) and air route surveillance radar (ARSR). Radar is used primarily in sequencing and spacing aircraft and can be used independently or in combination with other navigational aids.
Air Route Traffic Control Centers
Air route traffic control centers (ARTCCs or centers) primarily serve aircraft operating on instrument flight rules (IFR) flight plans within controlled airspace, principally during the en route phase of flight. There are 21 centers in the United States.
Types of Controllers
There are five basic types of air traffic controllers. Many air traffic controllers are trained and certified to work in multiple capacities.
Ground Controllers
Ground controllers direct aircraft that are moving on the ground, using the taxiways and parking ramps of airports.
Tower Controllers
Tower controllers direct aircraft that are taking off or landing at airports.
Departure Controllers
Departure controllers handle aircraft that have already taken off but are transitioning from the airspace around or near an airport to the en route portion of their flights.
Approach Controllers
Approach controllers handle aircraft that are transitioning from the en route portion of flight into the airspace around or near an airport.
Enroute Controllers
En route controllers handle aircraft that are operating on the main travel portion of their flights, typically at an altitude of 6,000 feet mean sea level (msl) or greater.
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Flight Plans |
One common misconception is that every aircraft must be issued a flight plan before it can fly. Flight plans are not required for flights conducted under visual flight rules (VFR), in which pilots navigate using references on the ground. Most flights take place without one. Just as when you use your car in daily life, pilots can take off and land at the vast majority of airports by using simple, pre-defined procedures, broadcasting their intentions over the radio so that they can coordinate their actions with other pilots in the area, using standardized traffic patterns, and complying with applicable Federal Aviation Regulations. |
VFR Flight Plans
A visual flight rules (VFR) flight plan has no air traffic control (ATC) significance. It's filed with ATC before the flight to facilitate the rescue of pilots and passengers in the very rare instance that the aircraft goes missing. Among other things, the VFR flight plan tells ATC what type of aircraft will be used and what colors it is, how much fuel is on board (expressed in hours and minutes of endurance), how many people are on board, the intended route and altitude of the flight, the anticipated time of departure, and the anticipated time en route (how long the flight will last).
How the VFR Flight Plan is Used
Once airborne, the pilot activates the flight plan by calling air traffic control (ATC) and telling them what time the flight actually took off. This starts a timer in the ATC system. When the pilot lands, he or she contacts ATC to tell them that he has arrived safely at the destination. ATC then "closes" the flight plan.
 If the pilot has not arrived and closed his flight plan within 30 minutes of his proposed arrival time, ATC will start calling by telephone to see if the flight has arrived. They may also contact other ATC facilities along the planned route of flight. Information in the VFR flight plan lets ATC know the maximum amount of time the aircraft could have stayed aloft based upon the fuel on board when it departed.
If, after a certain amount of time has passed, no one can locate the pilot or the aircraft, then ATC will launch a search and rescue operation using the Civil Air Patrol and/or the U.S. Coast Guard Auxiliary. Aircraft from the search team will retrace the intended route of flight, looking for the overdue aircraft. Information in the VFR flight plan lets searchers know what kind and color aircraft they are looking for and how many people were on board.
IFR Flight Plans
Instrument flight rules (IFR) flight plans contain the same information as visual flight rules (VFR) flight plans. However, IFR flight plans are used by air traffic control (ATC) to reserve the time and location of use for any airspace needed by the aircraft operating under IFR. The airspace needed by the IFR flight will be used exclusively by that aircraft from the time of takeoff until it has landed. Based upon the intended route of flight, pilots will be issued an IFR "clearance" to operate. In case of radio failure during the IFR flight, pilots will follow the exact route in the IFR clearance, and ATC will anticipate their path, altitudes, and times along the route based upon a combination of the IFR flight plan and the IFR clearance issued by ATC to the pilot. IFR flight plans can also trigger search and rescue operations if needed.
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