AIR TRAFFIC CONTROL

The United States air traffic management (ATM) system pro­vides services to enable safe, orderly, and efficient aircraft op­erations within the airspace over the continental United States and over large portions of the Pacific and Atlantic oceans and the Gulf of Mexico. It consists of two components, namely, air traffic control (ATC) and traffic flow management (TFM). The ATC function ensures that the aircraft within the airspace are separated at all times, while the TFM function organizes the aircraft into a flow pattern to ensure their safe and efficient movement. The TFM function also includes flow control such as scheduling arrivals to and departures from the airports, imposing airborne holding due to airport capac­ity restrictions, and rerouting aircraft due to unavailable air­space.

In order to accomplish the ATC and TFM functions, the ATM system uses the airway route structure, facilities, equip­ment, procedures, and personnel. The federal airway struc­ture consists of lower-altitude victor airways and higher alti­tude jet routes (1). The low-altitude airways extend from 1200 ft (365.8 m) above ground level (AGL) up to, but not including,

18,0 ft (5486.4 m) above mean sea level (MSL). The jet routes begin at 18,000 ft (5486.4 m) and extend up to 45,000 ft (13,716 m) above MSL. A network of navigational aids mark the centerline of these airways, making it possible to fly on an airway by navigating from one navigational aid to the other. The airways are eight nautical miles wide. Figure 1 shows the location of the jet routes and navigation aids that are within the airspace controlled by the Oakland and Los Angeles Air Route Traffic Control Centers. The jet routes are designated by the letter J, such as J501. Navigation facilities are indicated by a three-letter designation such as PYE.

Four types of facilities are used for managing traffic. They are the flight service stations (FSSs), air traffic control towers (ATCTs), terminal radar approach controls (TRACONs), and air route traffic control centers (ARTCCs) (1). These facilities

J. Webster (ed.), Wiley Encyclopedia of Electrical and Electronics Engineering. Copyright © 1999 John Wiley & Sons, Inc.

AIR TRAFFIC CONTROL

provide service during different phases of flight. The flight service stations provide preflight and inflight weather briefings to the pilots. They also request the flight plan infor­mation which consists of the departure and arrival airports, airspeed, cruise altitude, and the route of flight, which they pass on to the ARTCCs. Flight plan filing is mandatory for flight operations under instrument flight rules. It is not re­quired for flight operations under visual flight rules but it is highly recommended. The ATCTs interact with the pilots while the aircraft are on the ground or shortly into the flight. During a part of the climb, the TRACONs are responsible. TRACON airspace, known as terminal control area (TCA), is in the shape of an upside-down wedding cake. At higher alti­tudes, the ARTCCs take on the responsibility for providing the ATM services to the aircraft. The process is reversed as the aircraft nears the destination airport.

The main types of equipment used in ATM are the radars, displays, computers, and communications equipment. Radars provide information regarding the positions of the aircraft within the airspace. This information is processed in conjunc­tion with the flight plans to predict future locations of the aircraft. The display of this information is used by the air traffic controllers in the facilities to determine if the estab­lished rules and procedures would be violated in the near fu­ture. To prevent violations, the air traffic controllers issue clearances to the pilot to modify the flight path of the aircraft such as to speed up, slow down, climb, descend, and change heading. The procedures used by the air traffic controllers and pilots include rules and methods for operations within the particular airspace. For example, the rules define the minimum separation distance between any two aircraft, the authority of an individual facility over the airspace segment, the transfer of responsibility from one facility to the other, and the phraseology for verbal communications. For pilots, these rules specify their responsibility and authority, flight and navigation procedures, reporting requirements, and com­pliance with ATM instructions. The communications equip­ment enable both voice and computer-to-computer communi­cations. Voice communication is used between pilots and the ATM facilities and also between ATM facilities. Information transfer from one facility computer to the next is done using the communications equipment.

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