Air traffic at some three dozen airports across the US has been disrupted by a computer glitch, the Federal Aviation Administration says.
The network problem hit an FAA flight plan processing facility near Atlanta, Georgia, leaving a hub in Salt Lake City to handle data for the entire US.
The FAA said air safety was not affected and systems were returning to normal by late on Tuesday.
The Department of Homeland Security said there was no link to terrorism.
The network glitch began at about 1330 local time (1930 GMT), triggering delays at airports coast-to-coast.
FAA spokeswoman Kathleen Bergen in Atlanta said: "There will be flight delays. It could be any location, because one facility is now processing flight data for everybody."
The problem would be fixed by Tuesday evening, the FAA told Reuters news agency.
Airports in Boston, Baltimore, Charlotte, Atlanta and Chicago were facing major delays, some because of weather, the FAA said.
Flights to and from Washington, Miami, Cleveland and Houston were reported to be unaffected.
The cause of the failure remains unknown, but officials ruled out computer hacking attacks as well as terrorism.
The delays affected planes taking off, but not those landing. Glitch【電】短暫的電磁波干擾,短時脈衝波干擾 Disrupt 使混亂,使中斷 Hub (輪)轂;(推進器的)旋翼葉轂 Trigger 啟動裝置