The FAA is about to enter a critical phase in its transition to satellite-based airspace management, with the debut of a system that will for the first time allow controllers to separate traffic at major airports using satellite surveillance.

The nationwide deployment of Automatic Dependent Surveillance-Broadcast has already begun, but these initial sites have been limited to broadcasting information to aircraft. Now, contractor ITT Corp. is installing the first "critical-service" ADS-B system at Louisville, Ky., which will bring GPS-derived data to controllers' displays. While ADS-B has been employed for air traffic control before, the FAA will break new ground by using it to provide standard 3-mi. aircraft separation in terminal airspace, says Vincent Capezzuto, the agency's program head.

ITT is completing field testing of the system that is being deployed to Louisville, says John Kefaliotis, the company's ADS-B program manager. The FAA is expected to make its site-acceptance decision by early May, signaling that the system meets the agency's needs. Site acceptance "will be a big milestone for us," says Capezzuto. While there are always small problems discovered during this process, "it's all looking good so far."

Meanwhile, the FAA will be working on its ATC automation system at Louisville to allow the fusing of radar and ADS-B data. Validation testing will be done through the agency's technical center near Atlantic City, N.J., and at the Louisville terminal radar approach control (Tracon), so a safety case can be proven. The Louisville system is scheduled to go to initial operating capability status - handling live traffic - in October.

The controllers at Louisville won't see much difference on their displays, but the data feeds will be coming in from both ADS-B and radar. This offers safety and efficiency advantages. ADS-B is more reliable, as malfunctions are far rarer than with radar systems. It updates data much faster, improving the accuracy of traffic-conflict probes and aircraft separation, and coverage will be superior. In general, the ATC system "is going to operate better if the information going in is better," says Capezzuto. From the pilot's perspective, ADS-B will unlock a range of new applications (see p. 38).

In addition to the Louisville Tracon, three other key sites have been selected for ADS-B critical services: the Houston en route center (for Gulf of Mexico coverage); the Anchorage, Alaska, center (for Juneau coverage), and the Philadelphia Tracon. ADS-B is slated to be operational in Houston in December, Philadelphia next February, and Anchorage in April.

It is important that all these sites be ready by April 2010, notes Capezzuto. That is when the FAA wants to publish its long-awaited rule on ADS-B aircraft equipage, and the agency needs to be able to prove it can use this system to provide separation at all its facilities.

Part of the reason these four sites were selected is that they represent a good spread of the ATC systems used by the FAA. For example, Louisville has Common ARTS, Houston will have the new En-Route Automation Modernization (ERAM) system, and Philadelphia has the Standard Terminal Automation Replacement System (Stars). The ASDE-X surface surveillance system is also at Philadelphia, and its data will be incorporated into the ADS-B feed.

The FAA also chose these airports because levels of equipage were high among users, says Capezzuto. They represent "targets of opportunity" where the agency knows it can gather a lot of data even before the ADS-B rule is introduced.

For example, freight carrier UPS has equipped more than 100 of its aircraft for ADS-B at its Louisville hub. UPS also operates many flights into Philadelphia, and US Airways has signed a deal with the FAA covering equipage at this airport. At Juneau, many aircraft are already ADS-B capable, thanks to an earlier program in Alaska.