LOS ANGELES (AP) -- The failure of the primary air traffic control system around Los Angeles last week happened because electronic data from a single plane's flight plan confused the system's software, according to the Federal Aviation Administration.
When that system failed, a backup helped safely guide flights already in the air, but hundreds of planes across the nation headed for Southern California were ordered not to take off Wednesday as an air traffic control facility north of Los Angeles effectively rebooted.
The Pentagon confirmed Monday that an Air Force U-2 spy plane was conducting training operations in the area. It is not unusual for a U-2 to operate in the region, and the necessary flight plan had been submitted for the high-flying plane, Col. Steve Warren said.
FAA spokesman Lynn Lunsford would not specify whether the flight plan that caused the issue was that of the U-2.
"It was an individual flight plan and the issue had to do with the way it was coded," he said.
Since the incident, the FAA has been analyzing what went wrong with its En Route Automation Modernization system. The computer system, known as ERAM, allows air traffic controllers at several dozen "en route centers" around the country to identify and direct planes at high altitudes.
The Los Angeles en route center is located at the Palmdale Regional Airport, about 40 miles north of Los Angeles. It controls high altitude air traffic over southern and central California, southern Nevada, southwestern Utah and western Arizona — except airspace designated for military use.
When the system went down, air traffic controllers in Palmdale had to call their counterparts at neighboring centers to update them on each plane's flight plan, according to Nate Pair, the president for Los Angeles Center of the National Air Traffic Controllers Association. While that was more onerous than normal operations — when computers automatically pass along updates — the system still worked, Pair said.
"Not knowing why it was happening is the reason why we decided to shut everything down," he said. "They're searching to find the cause of the glitch, and we're waiting analysis on that."