During peak travel hours, as many as 5 000 airplanes fly in the continental United States. How can each airplane be sure to take off and land safely, avoiding the others? Air traffic control coordinates all air travel, directing takeoffs and landings, ensuring safe distances between airplanes, and keeping routes away from bad weather. The air traffic control system forms a seamless web across all private commercial airline flight. As an airplane travels, a well-defined authority, or responsibility for the flight, is passed from one air traffic controller to the next. Smooth transfer of authority ensures safe travel; this authority passes from the most local level, at airport control towers, to the most national level, at centralized national facilities, and back again during fight.

Prior to takeoff, the airplane's path is guided by local air traffic controllers located in towers near the airport. These controllers make a record of each departing flight, direct all ground traffic on the airport runways, and determine when it is safe for airplanes to take off. Once an airplane is cleared for takeoff, the pilot is in control, but authority for the flight is transferred to the TRACON facility nearby. After this transfer, the pilot of the flight speaks with a newly assigned controller.

The TRACON (Terminal Reader Approach Control) area covers a fifty-mile radius around a control tower. This area may include several airports. A controller in this facility dictates to the pilot what path to follow on ascent, making sure that the corridor is clear and a safe distance is maintained between this and other departing aircraft.

When the flight departs TRACON airspace, authority is transferred to an Air Route Traffic Control Center (ARTCC). These regional control centers, of which 21 exist in the continental US, cover zones roughly equal in area and centered around major airports. ARTCC controllers communicate with national level controllers, who direct flights around bad weather, turbulence, and inactive runways.

Given the enormous volume of air travel and its ongoing growth, improved information systems are needed to assist air traffic controllers. TRACON controllers direct an aircraft's final approach, before transferring authority back to local airport air traffic controllers. They coordinate several planes approaching from different directions into a closely spaced, single-file line. This task, like much of air-traffic control, requires superb three-dimensional visualization skills and split-second decision-making abilities. Only computer-controlled direction systems can help lighten the difficult burden placed on the TRACON staff.