"Philadelphia certainly marks a major milestone -- it's the first use at a high-volume airport," said Federal Aviation Administration spokesman Greg Martin.
The $1.3 billion STARS, for Standard Terminal Automation Replacement System, has been denounced as flawed.
The equipment doesn't always give a reliable picture of area traffic, according to the General Accounting Office, the Transportation Department inspector general and the union representing FAA employees who certify and maintain equipment.
FAA officials worked all last week to decide whether the system was ready to go.
Limited versions of STARS are in a handful of smaller airports such as El Paso, Texas, where air traffic controllers complained they sometimes couldn't tell the difference between a truck on the interstate and a plane on the runway, said Tom Brantley, spokesman for the Professional Airways Systems Specialists, which represents the people who maintain the system.
The GAO said the system's software had bugs that needed to be fixed.
"These problems, if not corrected, might prevent FAA from using STARS to control air traffic and might jeopardize safety," the GAO said.
The agency and the manufacturer have been ironing out the software problems.
Martin said FAA officials will continuously evaluate the system in Philadelphia and won't decide to phase it in fully until they're sure it's safe. The current system will also be available for controllers as a backup, he said.
"It's not as if you flip the switch and it's all STARS all the time," he said.
FAA and the unions were also concerned there wasn't enough time to train everyone on the new system before going ahead with it in Philadelphia. Martin said the agency has been working with the unions to make sure controllers and maintenance technicians are trained on the system.
Eventually, STARS will be installed at dozens of sites where controllers track planes from takeoff to cruising altitude. It will replace several different models of computers now in use and offer full-color displays instead of monochrome. It contains weather maps and can be expanded to produce more detail about storms.
Brantley said the screens occasionally display weather that doesn't exist. Too much weather information, he said, can overload the system and cause it to crash.
"Our biggest problems are not with Philadelphia, they're with the 73 other sites that will get this after they declare victory in Philadelphia," Brantley said.
Martin said the FAA will involve local unions as it installs STARS around the country.
"We'll work through the issues and we'll go to the next site and the next site and the next," he said.
STARS has also been plagued by cost overruns and delays.
In 1996, the FAA planned to install STARS at 172 facilities beginning in 1998 at a cost of $940 million. Plans now call for 74 facilities at a cost of $1.3 billion; the first systems went online this year, four years behind schedule.
STARS is also in Syracuse, N.Y.; Memphis, Tenn.; Hartford, Conn.; Birmingham, Ala.; Albuquerque, N.M.; Detroit; Albany, N.Y.; and Providence, R.I.
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