In a bid to modernize the U.S. air traffic control system and avert air travel gridlock, the Federal Aviation Administration has formulated a 10-year, $11.5 billion plan to replace today's radar-based system with one built around satellites. The project relies largely on Global Positioning System data, rather than radar, for navigation. The problem is that GPS still isn't accurate or reliable enough for such aviation applications. Now, a system that would allow GPS to provide nearly infallible signals for air traffic use is getting ready for rollout. If the technology passes testing over the next several years, it could help make the FAA's grand vision a reality.

In the new system, 25 ground stations constantly check the accuracy of the GPS signal. Software corrects glitches caused by things like atmospheric disturbances, and the stations beam corrected information to pilots via a pair of satellites. After seven years of trying, Raytheon of Lexington, MA, is expected to deliver the system as early as March 2003, the FAA says. "Everything is really coming to a head," says Timothy Katanik, a Raytheon manager working on the system. "We think we are there now."

Satellite-based air traffic control promises greater flexibility and capacity than radar-based systems (see "The Digital Sky," TR March 2001). Pilots could freely optimize their routes and not herd themselves into clogged "highways" set by radar beacons. And when landing in bad weather, pilots could use satellite data to follow a variety of approach patterns, instead of the single rigid path required by runway landing signals. All this could mean shorter trips and fewer delays.

Refinement of GPS signals won't come cheap, though. And additional ground stations based near each airport will be needed for, say, landings in zero visibility. The total cost could run as high as $4.6 billion, says Hal Bell, the FAA's product leader on the system. And don't expect fewer delays at LaGuardia anytime soon. GPS will initially just help pilots land at remote airports that currently lack radar; FAA approvals for large, busy airports, and for zero-visibility landings and other tough situations, could take up to 20 years, Bell says. Which means passengers could be waiting for improved on-time rates for quite a while.