Officials say a breakdown in the communications system linking Greek airports prevented flights from taking off for two-and-a-half hours.
They say takeoffs were stopped at all airports at 8:30am (0530 GMT) Sunday. Athens International Airport says that flights resumed around 11am. (0800 GMT).
The cause of the breakdown is unknown. The head of the civil aviation employees' union told a radio station that the system was last upgraded 17 years ago.