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, Ca. The L.A. Center handles landings and departures at the region’s major airports, including Los Angeles International (LAX), San Diego and Las Vegas.

“FAA technical specialists resolved the specific issue that triggered the problem on Wednesday, and the FAA has put in place mitigation measures as engineers complete development of software changes,” said the agency in a statement. “The FAA will fully analyze the event to resolve any underlying issues that contributed to the incident and prevent a reoccurrence.”

Sources told NBC News that the plane was a U-2 with a Defense Department flight plan. “It was a ‘Dragon Lady,’” said one source, using the nickname for the plane. Edwards Air Force Base is 30 miles north of the L.A. Center. Both Edwards and NASA’s Dryden Flight Research Center, which is located at Edwards, have been known to host U-2s and similar, successor aircraft.

More: Spy Plane Fries Air Traffic Control Computers, Shuts Down LAX - NBC News.com