Air Traffic Management System

Center or Air Route Traffic Control Center (ARTCC)

The first Air Traffic Control Center originated at Newark Airport, Newark, New Jersey, as a privately operatedventure formed by cooperative airline companies in October 1935. On July 8, 1936 the Department of Commerce's CivilAeronautical Administration assumed operation of the air traffic responsibilities.

ARTCCs, usually referred to as "Centers," areestablished primarily to provide Air Traffic Service to aircraft operating on IFR flight plans within the controlledairspace, and principally during the en route phase of flight. There are 21 Air Route Traffic Control Centers (ARTCC)in the United States. Any aircraft operating under Instrument Flight Rules (IFR) within the confines of an ARTCC'sairspace is controlled by air traffic controllers at the Center. This includes all sorts of different types ofaircraft: privately owned single engine aircraft, commuter airlines, military jets and commercial airlines.

The Federal Aviation Administration has made a long-terminvestment of tax dollars by providing the finest air traffic control service in the world. The largest componentof the national airspace system is the Air Route Traffic Control Center (ARTCC). Each ARTCC covers thousands ofsquare miles encompassing all or part of several states. ARTCCs are built to ensure safe and expeditious air travel.All Centers operate 7 days a week, 24 hours a day and employ a combination of several hundred Air Traffic Control Specialists, Electronic Technicians, Computer System Specialists, Environmental Support Specialists, and administrative staff.


Safe Separation Standards
The primary means of controlling aircraft is accomplished by using highly sophisticated computerized radar systems. In addition, the controller maintains two-way radio communication with aircraft in his/her sector. In this way, the specialist ensures that the aircraft are separated by the following criteria:

  • Laterally -- 5 miles
  • Vertically --
    • 1,000 feet (if the aircraft is below 29,000 feet)
    • 2,000 feet (if the aircraft is at 29,000 feet or above)

The controllers can accomplish this separation by issuing instructions to the pilots of the aircraft involved. Altitude assignments, speed adjustments, and radar vectors are examples of instructions that might be issued to aircraft.

En Route control is handled by pinpointing aircraft positionsthrough the use of flight progress strips. These strips are pieces of printed paper containing pertinent informationextracted from the pilot's flight plan. These strips are printed 20 minutes prior to an aircraft reaching eachCenter's sector. A flight progress strip tells the controller everything needed to direct that aircraft. If theflight progress strips of each aircraft approaching a sector are arranged properly, it is possible to determinepotential conflicts long before the aircraft are even visible on the Center controller's display. In areas whereradar coverage is not available, this is the sole means of separating aircraft.

The strips, one for each en route point from which the pilotwill report his/her position, are posted on a slotted board in front of the air traffic controller. At a glance,he/she is able to see certain vital data: the type of airplane and who is flying it (airline, business, private,or military pilot), aircraft registration number or flight number, route, speed, altitude, airway designation,and the estimated time of arrival at destination. As the pilot calls in the aircraft's position and time at a predeterminedlocation, the strips are removed from their slots and filed. Any change from the original flight plan is notedon the strips as the flight continues. Thus, from a quick study of the flight progress board, a controller canassess the overall traffic situation and can avoid possible conflicts.

Follow this link for more information about a Center's flightprogress strip.


Ft. Worth ARTCC geographical coverage area


Record of traffic in the Fort Worth ARTCC


There are 18 low altitude sectors. 


There are 16 High Altitude Sectors


There are 16 High Altitude Sectors


There is 1 Ultra High Altitude Sector

The Fort Worth Air Route Traffic Control Center (ZFW) is a typical ARTCC. The Center has approximately 350 controllers. Most are certified and some are in on-the-job training. The Ft. Worth ARTCC geographical coverage area is shown below.

Fort Worth ARTCC area map image

There are 4 En Route Centers adjacent to Fort Worth Center. In addition,
there are 5 ATC Towers inside ZFW airspace and 19 radar approach
control facilities that work directly with Fort Worth Center. Fort Worth
Center also provides approach control services to 85 public and private
use airports with instrument approach procedures. There are 148 public and private use airports in the DFW terminal area. Demand on airspace is very high and presents complex traffic situations in both the terminal and En Route environments.

A record of traffic in the Fort Worth ARTCC during a two hour period is shown on the left.

Yellow lines represent arrivals and green lines display departures. The red lines show the aircraft that are flying through the sector. These are called “over flights.”

The Fort Worth Center's airspace is split up into smaller, manageable pieces of airspace called "sectors". Sectors have vertical as well as horizontal boundaries. A few sectors extend from the ground up, but most areas are stratified into various levels to accommodate a wide variety of traffic.

Each sector has a unique radio frequency that the controller uses to communicate with the pilots. As aircraft transition from one sector to another, they are instructed to change to the frequency of the next sector.

There are 18 low altitude sectors. 

There are 7 Intermediate Altitude Sectors.

There are 16 High Altitude Sectors

There is 1 Ultra High Altitude Sector

From one to three controllers may work a sector, depending upon the traffic density. Each controller is assigned to work the positions within an area of specialization. There are 7 areas of specialization at Fort Worth Center. Controllers have direct communication with pilots, with surrounding sectors and Centers, plus the Towers and Flight Service Stations under their jurisdiction. Each control position is equipped with computer input and readout devices for aircraft flight plan data.

In general there are 3 basic controller positions working together to monitor and direct traffic within the Center’s airspace.

  • Radar Controller
    This controller is in charge of the sector. This controller maintains positive separation among all aircraft under his/her control. Separation standards from a Center are defined as 5 miles laterally or longitudinally for aircraft flying at the same altitude, or 1,000 feet vertical separation below 29,000 feet and 2,000 feet vertical separation above 29,000 feet. The radar controller is responsible for all air-to-ground communications. Coordination with other sectors and facilities is a duty shared by both the radar controller and the associate controller.
  • Associate Controller
    The radar associate controller assists the radar controller and receives flight plan information on aircraft anywhere from 5 to 30 minutes in advance of aircraft entering the sector. The associate controller works with the radar controller to plan separation of aircraft and to coordinate with other sectors and facilities.
  • Radar Hand-off
    This controller assists the radar team when air traffic becomes very heavy. The hand-off controller serves as another set of eyes to maintain separation of aircraft and coordinate with other controllers and facilities as necessary. This extra help also serves to maintain a smooth and efficient flow of air traffic.

Controllers in each Center work at a console that displaysthe radar data, allowing controllers to see the aircraft within their airspace. The display consists of variouslines, letters, numbers and symbols that aid the controllers. The sector boundaries show the lateral limits ofthe sectors. Circles denote the location of ground based navigation stations. Lines extend outward from these navigationstations showing the location of airways. Aircraft are represented on the display as slashes.

Each aircraft has a data block associated with it that givesthe controller important information.

  • The first line of the data block shows the aircraft's call sign.
  • The second line shows its altitude. If there are two numbers on this line, the aircraft is either climbing or descending. The first number of these 2 numbers shows the assigned altitude with the second of the 2 numbers displaying the aircraft's actual altitude. An arrow indicates if the aircraft is climbing or descending.
  • The third line of the data block contains two primary pieces of information. The first three numbers show the aircraft's Computer ID number (CID). The controller uses this number frequently to update information associated with this aircraft. If the controller needs to change some information about this aircraft, he/she can use this CID rather than a lengthier call sign. The other numbers on the third line show the aircraft's speed across the ground.



The Center controllers have many decision supporttools (computer software programs) that provide vital information to assist the controllers in maintaining safeseparation distances for all aircraft flying through their sector. One such predictive tool allows the controllerto display the extended route of any aircraft on the radar screen. One such route is called a "vector line."This line projects where the aircraft will be within a specified number of minutes, assuming the aircraft doesnot change its course. This is a helpful tool to determine if aircraft flying intersecting routes will pass safelywithin the separation standard, or if they will conflict with each other.

In addition to vector lines, the controller can also displaya "route line" for any given aircraft on his/her radar screen. This will tell the controller where aparticular aircraft will be in specified number of minutes as well as the path the aircraft will fly to get there.Decision support tools such as these help each controller look ahead and avoid conflicts.