The vast majority of flights are not handled by air traffic control (ATC). Surprised? You shouldn’t be; just think about how you use your car on a daily basis. No one provides permission for you to leave your driveway or tells you how to enter or leave the parking lot at the mall. Throughout your trip, you follow well-known procedures referred to as "rules of the road." The same is true of all pilots. Basic techniques taught to every pilot facilitate the safe and orderly flow of traffic. But high volume areas and flights in bad weather conditions require monitoring and direction by ATC.

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 314 FAA airport control towers in the United States. More than 210 federal contract towers and 165 military towers also help separate aircraft. There are also 22 terminal radar approach facilities (TRACONs), some of which are collocated with airport control towers.

Airport Surveillance Radar

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

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.

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.