Until the final report is published of the Boeing 757/Tupolev Tu-154 midair collision over Switzerland on July 1, there will probably be continuing speculation about the role that ATC radar played in the accident. Yet there need be no speculation at all about radar’s role in the U.S. National Airspace System. It is, quite simply, the foundation upon which the system has been built. In the almost 60 years since the end of World War II, the FAA and its predecessor agencies have progressively updated the nationwide radar network as technology has advanced. The latest advance is the user request evaluation tool (URET).

Developed by the Mitre Corp., a government research organization, and built by Lockheed Martin, URET is an extremely smart radar computer program that continuously monitors the present position of all aircraft in the radar’s view and accurately predicts their future positions, out to 20 min flying time ahead. Should it detect a potential conflict, it immediately alerts the controller of the sector in which the affected aircraft are currently flying, maximizing the warning time.

In some sense, each radar control position at an FAA ARTCC is similar to a flight deck, with two controllers at each position, working together as a team to cover an assigned airspace sector. One is called the R (radar) controller, and the other is the D (data) controller, and their relationship is broadly analogous to that of a captain and a first officer. The R controller monitors the radar display and continually makes mental calculations of potential conflicts. Whenever conflicts–or, more commonly, losses of minimum separation–appear likely in a non-URET ARTCC today, the R controller must be ready to transmit a resolution maneuver to the aircraft involved, usually in less than three minutes. In high-density terminal areas, the R controller can be busy.

The D controller also monitors the radar screen, but looks further ahead for longer-term strategic problems while coordinating traffic movements with other sectors within his own and neighboring ARTCCs. In non-URET installations, the D controller manages the steady flow of the traditional paper strips that individually summarize the flight plans of each aircraft passing through the sector.

In the URET installation, the D controller still monitors the radar and communicates with aircraft in the sector, but the need for quick mental calculations is considerably eased with the addition of the slightly smaller URET screen beside his radar display. This shows a similar traffic picture but, in the event of a potential conflict, it is instantly overlaid with the URET’s conflict prediction–typically a pair of bright red lines on the screen showing the projected tracks of the conflicting aircraft, converging on the point where loss of safe separation (less than five miles) could occur. The URET screen can also display an electronic list of individual flight plans, presented in a similar format, but now replacing, the earlier paper strips.

Should the predicted separation