A radio frequency malfunction which caused a partial shutdown in flights across Greece for hours soon after New Year’s Day was due to outdated systems rather than external interference, according to the findings of a probe made public Tuesday.

The Infrastructure and Transport Ministry said a committee of experts investigating the Jan. 4 incident stated in its report that “no indications of cyber attack or external malicious interference” were found.

A ministry statement said the civil aviation authority’s voice communication system and crucial telecom systems used to support it are “based on outdated technology that is no longer supported by the manufacturer,” which cannot offer “effective guarantees for its operation.”

The ministry said the report recommended a speedy transition to Voice over IP technology in communications systems, through the purchase and installation of a new voice and radio communication system and nearly 500 new transceivers. It also called for creation of a common immediate response mechanism between the civil aviation authority and telecoms providers.

It said the report faulted “digital noise” involving a loss of synchronization in systems leading to  the Athens and Macedonia regional control center, which caused a “critical number” of beacons to malfunction, shutting down “crucial telecoms connections.” The system was restored just before 5 p.m. on Jan. 4 after being restarted.

The radio frequencies serving the affected center had gone out of operation in the morning, grounding planes and affecting schedules, while aircraft already in the air continued to operate normally. 
The statement also said that the incident was assessed as low-risk.

“No issue of aviation security, in the sense of aircraft being exposed to direct or indirect threat, was noted,” it said.