FAA SAYS UPKEEP NOT DONE MAINTENANCE LAPSE CITED BY AGENCY FOR RADIO FAILURE.

Byline: Charles F. Bostwick Staff Writer

A lapse in routine maintenance was blamed Wednesday for the shutdown of the air traffic communications system serving Southern California, resulting in as many as five close calls in the skies as service was disrupted for more than three hours, the officials said Wednesday.

During the first 13 minutes of Tuesday's communications blackout, cockpit alarms sounded in six jets, warning of a potential collision, and four other planes got close enough to violate Federal Aviation Administration separation standards, officials said.

``It was very dangerous,'' said Mark Sherry, a spokesman for the National Air Traffic Controllers Association. ``This is as ugly as it gets, short of running two airplanes together. We could have had 10 airplanes go down.''

Federal Aviation Administration officials insisted there was never a danger of a midair collision, and that the blackout could have been avoided if a required 30-day maintenance check on the primary radio and voice communications system had been performed.

``There were no software glitches, there was no component failure. There was human error. We failed to do the maintenance,'' FAA chief spokesman Greg Martin said.

FAA officials said they were modifying communications systems nationwide to prevent further failures. They also were trying to find out why the maintenance was not performed and why the backup system was not configured properly to take over.

``We believe the reason that hadn't got done during maintenance was because the person doing the maintenance hadn't been trained,'' said Ray Baggert, a regional officer of the Professional Airways Systems Specialists, the union representing the industry's technicians. ``We have such short staff they can't get people out to get training.''

The center was tracking about 400 planes when the blackout occurred about 4:40 p.m. Tuesday, stranding tens of thousands of travelers at LAX and other Southern California airports and forcing diversion of incoming flights to other airports.

The computerized radio system is used by controllers in the Los Angeles Air Route Traffic Control Center in Palmdale to talk to pilots and other control centers.

After that failed, a technician switched to the backup system, but that quickly shut down, too, officials said.

Within minutes, a Northwest 757 traveling at 35,000 feet from Detroit to San Diego came within 0.9 miles and 900 feet vertical of a Gulfstream III business jet climbing out of Long Beach, controllers said. FAA officials said the planes were 1,400 feet apart vertically.

A UPS 757 heading to Orange County from Louisville, Ky., at 35,000 feet came within 1.9 miles and 1,000 feet vertical separation from a Cessna Citation business jet heading out of Phoenix, controllers said. The FAA said the planes were 1,100 feet apart vertically.

Under FAA ``separation standards,'' planes flying higher than 29,000 feet must remain at least five miles apart horizontally, and no less than 2,000 feet apart vertically.

The other aircraft that experienced close calls were not identified.

Within minutes of the breakdown, the aircraft being tracked by the Palmdale center were taken over by centers in Denver, Albuquerque and Oakland, as well as the Phoenix airport tower and Southern California's radar approach and takeoff control center in San Diego, FAA officials said.

The FAA said the failure occurred because a monthly maintenance procedure, instituted nationwide last year after a less-disruptive communication failure in Atlanta, was not performed, and the backup system was not configured to take over properly.

Revised software was developed and tested after the Atlanta failure, has been installed in Seattle and is being installed nationwide, officials said.

Similar failures have occurred in Houston and elsewhere, but the backup communication system worked in those instances, officials said.

After Tuesday night's failure, the FAA rechecked each of its air route centers to make sure that the monthly maintenance procedure - called a ``buffer purge,'' and equated to rebooting a computer processor - was being followed.

While the communication system is about 7 years old, the new procedure was instituted after an upgrade about two years ago to replace an computer that grew too old to get parts for, said Steven Michaleski, the Palmdale spokesman for the union representing maintenance technicians.

Air route centers such as the one at Palmdale control airliners and other planes as they fly from airport to airport. They give pilots instructions, air traffic clearances and advice regarding flight conditions, and keep the planes flying at safe distances.

Controllers hand off direction of aircraft to controllers in adjacent centers, or to approach control centers. Airport towers take over control a few miles from the airport.

Charles F. Bostwick, [phone]

chuck.bostwick(at)dailynews.com