A technical issue on Monday caused delays to flights through all of Scotland's main airports, a media report said.
Edinburgh, Glasgow, Aberdeen and Prestwick airports have been affected by the incident at the Scottish Air Traffic Control centre at Prestwick, BBC reported.
Air traffic controllers Nats said the cause has been identified and was being resolved.
It apologised for the inconvenience being caused but said the situation was improving.
One traveller tweeted to say they were "stuck on a plane" at Glasgow airport.