‍ATHENS — Flights across Greece were grounded for several hours on Sunday after a collapse of aviation radio frequencies disrupted communications between aircraft and air-traffic controllers, forcing authorities to temporarily shut Greek airspace and stranding thousands of passengers at peak holiday-season demand.

The disruption began at 8:59 a.m. local time (0659 GMT), when what officials described as a continuous “noise” signal interfered with radio channels used by aviation authorities. With controllers unable to reliably talk to pilots, Greek airspace was effectively closed as a precautionary measure, with only overflights permitted.

Airports across the country quickly filled with delayed passengers as dozens of flights were suspended. Greece’s civil aviation authority said the source of the interference remained unclear but described the scope of impact as unprecedented.

“For some reason all frequencies were suddenly lost. We could not communicate with aircraft in the sky,” said Panagiotis Psarros, chair of the Association of Greek Air Traffic Controllers.

He later warned the incident exposed vulnerabilities in an aging communications network that “should have been replaced many years ago.”

By mid-afternoon, services gradually resumed after aircraft were moved onto backup frequencies. Authorities said departures had recovered to around 45 flights per hour by late Sunday, and Transport Minister Christos Dimas stressed that safety was never compromised.

The outage, which impacted both ground and approach-control channels, including those supporting Athens’ Eleftherios Venizelos International Airport (ATH), is now under investigation.

The incident occurred during one of Greece’s busiest winter travel weekends and renewed calls from controllers for modernization of critical navigation infrastructure.

Airways will continue to monitor developments.