SUMMER afternoon thunderstorms are temporarily knocking out new radar systems in South Florida, forcing air-traffic controllers to delay take-offs and landings by a half-hour.
''My confidence and the confidence of a lot of the controllers in this building is severely eroded by what's happening,'' says Steve Elmore, an air-traffic controller at Miami International Airport. ''This is a real concern especially when as many as 230 planes fly over South Florida per hour during the peak hours.''
Lightning strikes have knocked out the radar systems in Miami and at Ft. Lauderdale-Hollywood International Airport a combined 25 times in the last six weeks. Particularly vulnerable is the radar's Mode-S system, which provides an airplane's call signs, destination, speed, and altitude. Federal air-safety technicians have since found that improper grounding and wiring turned the multimillion-dollar Airport Surveillance Radar 9, or ASR9, into a lightning rod.
Miami and Ft. Lauderdale are not the only airports that use ASR9, nor the only places where the new system has had problems. Air-traffic controllers in dozens of the 101 airports that use ASR9, including Detroit, Salt Lake City, Cleveland, and Memphis, have filed complaints. Problems include power surges, failures after lightning strikes, aircraft disappearing from radar screens, and the sudden slowdown of the radar sweep across the screen.
Although none of the failures or glitches have led to accidents, there have been several near-misses. One near-miss occurred over Ft. Lauderdale shortly after ASR9 was installed. The air-traffic controller on duty blamed ''radar problems'' for the near-disaster.
Another incident in January 1994 at Detroit-Wayne Airport involved an actual collision on the radar screen. But, in reality, it was a real aircraft and a phantom plane that suddenly appeared on the display that the controller saw collide. As if to explain the problem in the incident report, the controller simply states: ''We have ASR9.''
The ASR9, which was developed in 1989, was installed at Miami and Ft. Lauderdale in May. Both airports have back-up systems, but those systems have often failed. That's left air-traffic controllers scrambling to turn on a third back-up system for tracking long-range flights. Switching to long-range radar, though, can take up to five minutes, and controllers can lose track of aircraft for miles. In one minute of radar failure, a fast-moving aircraft can travel up to six miles without being tracked.
''For an air-traffic controller, there is no more frightening experience than watching your radar screen go blank,'' says Andrew Cantwell, president of the Miami local of the National Air-Traffic Controllers Association. ''It creates a very tense working environment for the controllers. Our job is very stressful at the best of times.''
While the Federal Aviation Administration maintains that passenger safety is not compromised, the agency now acknowledges that it no longer considers ASR9 as reliable as it once did.
''ASR9 is reliable 99.35 percent of the time,'' says Jerry Taylor, the FAA radar program manager. ''These lower figures [down from 99.9 percent] reflect some of the reliability problems we've had in the last three years.'' For an airport open 24-hours a day, this reliability rate would mean 10 minutes of downtime each day.
While the FAA promises that its technicians will soon rectify the problems, air-traffic controllers have already begun delaying take-offs and landings every afternoon - a peak time for thunderstorms in South Florida. The plan is meant to decrease the stress on controllers and increase safety for passengers. But this plan often means lengthy delays for air travelers.
Passengers have also expressed their own concerns about these radar failures and flight delays. ''A properly functioning radar system is something I've always taken for granted,'' says Robert Azhar, a New York banker. ''It worries me that my plane could just go blank on their screen.''
A Chicago-bound Sue Keenan understands taking proper precautions but not having ''a flight delay caused by a storm that hasn't even hit the airport.''
The FAA has rejected the assertion of union representative Cantwell that the present situation is ''unsafe.'' Even so, the FAA has dispatched an emergency technical team to Miami to figure out what is wrong with the radar system and how to fix it.