Aviation officials say a solar storm knocked out the air traffic control systems in Sweden on Wednesday, prompting them to close the country's airspace for more than an hour.
The civil aviation authority said the solar storm created disturbances in the Earth's magnetic field, which affected radar installations in southern Sweden. No such problems were reported in neighbouring countries.
Agency spokesman Per Froberg said flights disappeared from radar screens in Swedish air traffic control towers during the blackout, which lasted about an hour until 5:30 p.m. local time (11:30 a.m. ET). Froberg said it was unclear why the impact was so severe, adding the last time something similar happened in Sweden was in 1999.
"We're working on sorting out the delays. We can't examine the cause right now. We have our hands full," he said.
He couldn't say how many flights were affected, but the country's main airports listed dozens of delays.
Air traffic control officials in neighbouring Denmark and Finland say they didn't experience any problems.
"There haven't been any disturbances. Only a few delays in Copenhagen because of the problems in Stockholm," said Mette Just of Naviair, Denmark's air navigation service.