A relic from the Cold War appears to have triggered a software glitch at a major air traffic control center in California Wednesday that led to delays and cancellations of hundreds of flights across the country, sources familiar with the incident told NBC News.

On Wednesday at about 2 p.m., according to sources, a U-2 spy plane, the same type of aircraft that flew high-altitude spy missions over Russia 50 years ago, passed through the airspace monitored by the L.A. Air Route Traffic Control Center in Palmdale, Calif. The L.A. Center handles landings and departures at the region’s major airports, including Los Angeles International (LAX), San Diego and Las Vegas.

The computers at the L.A. Center are programmed to keep commercial airliners and other aircraft from colliding with each other. The U-2 was flying at 60,000 feet, but the computers were attempting to keep it from colliding with planes that were actually miles beneath it.

Though the exact technical causes are not known, the spy plane’s altitude and route apparently overloaded a computer system called ERAM, which generates display data for air-traffic controllers. Back-up computer systems also failed.