The airspace over London has been severely restricted, because of a "computer failure," Eurocontrol, the European flight safety body, said on Friday.
NPR's Ari Shapiro tells us many flights are expected to be grounded for more than three hours.
"The UK's National Air Traffic Control Center experienced a mid-afternoon power failure," Ari reports. "That forced Heathrow and other airports in the London area to stop all air traffic in and out. Heathrow is Europe's busiest airport, so this will have ripples all across the continent."
This is breaking news story. We'll have more as we get it.