Flights across ‌Greece were grounded on Sunday (January 4, 2026) after a ​collapse of radio frequencies crippled air traffic communication, stranding thousands of travellers and bringing airport operations to a halt.

There was little clarity on what caused the disruption, which began early Sunday (January 4) and quickly escalated. Some overflights across Greek and regional airspace were still being serviced, but ​restrictions were imposed on airport operations for safety reasons, ⁠Greece’s civil aviation authority said.

Dozens of flights were disrupted. “For some reason all frequencies were suddenly lost .. We could not communicate with aircraft ​in the sky,” Panagiotis ⁠Psarros, chair of the Association of Greek Air Traffic Controllers, told state broadcaster ERT.

He said the problem seemed to be a collapse of central radio frequency systems at ‌the Athens and Macedonia area control systems, the ‌largest air control facility in the country based in Athens. It monitors the Athens Flight ‍Information Region, a vast expanse of airspace under the control of Greek authorities.

Flight trackers showed Greek airspace was ‍largely empty. ERT said airport arrivals and departures were suspended at 9 a.m. local time (0700 GMT), reporting from a departures terminal at Athens’ Eleftherios Venizelos airport crowded with travellers.

“We haven’t been informed about the cause of this problem… certainly the equipment we have is virtually ancient. We have raised this many times in the past,” Psarros ⁠said.

A Transport Ministry official told Reuters some aircraft heading north and east were allowed to ​leave. More than 75 flights were delayed, the official said.

In Israel, ⁠an Airports Authority spokesperson said Greek airspace had been closed until 4 p.m. local time (1400 GMT), advising travellers to expect delays in arrivals and departures.