Flights across Greece were grounded on Sunday, January 4, 2026, due to a widespread collapse of radio frequencies used for air traffic control. The disruption, which began early Sunday, led to thousands of travelers being stranded and airport operations coming to a halt. While some overflights continued, arrivals and departures were suspended for several hours. The cause remains unclear, though the Association of Greek Air Traffic Controllers cited issues with central radio frequency systems and highlighted the age of the equipment. Limited services resumed by Sunday afternoon after pilots switched to backup frequencies.