Incident Overview
On July 9, 2015, a Boeing 737-800 (B738) entered the Warsaw Flight Information Region (FIR, EPWW) without having established radio communication with air traffic control. The flight was en route from Chania International Airport (LGSA) in Greece to Copenhagen Airport (EKCH) in Denmark.
Communication Attempts
Air traffic controllers at ACC Bratislava and ACC Warsaw repeatedly attempted to contact the crew on the designated frequencies, including the emergency frequency 121.5 MHz, but received no response. Another aircraft operated by the same airline was also asked to attempt contact using the company's traffic frequency and via ACARS messaging. The communication loss created a complex traffic situation in sector ACC "J", requiring controllers to alter the altitude of another aircraft to maintain safe vertical separation.
Re-establishment of Contact
Radio contact was finally achieved near the waypoint POLON after a call on 121.5 MHz by a crew member of another aircraft from the same operator. The crew of the B738 then switched to the Warsaw ATC frequency as instructed.
Captain's Account
In a statement provided to the Accident Investigation Board Norway, the captain of the B738 explained that during the cruise, they were contacted by company traffic on 121.5 and told to change over to Warsaw ATC, which they did. They were then informed that they had been without radio contact for a period of time. The captain noted that both pilots were awake and wearing headsets, with 121.5 selected. However, ACARS was not functioning at the time, and they received the message about 30 minutes late. The captain described the event as a mystery with no reasonable explanation.
Investigation Outcome
The Polish State Commission on Aircraft Accident Investigation (PKBWL) forwarded details of the flight's passage through Warsaw FIR to the Norwegian AIB to obtain further information. The investigation concluded with no determination of the probable cause. No preventive actions were taken by the operator, and no safety recommendations were issued by the commission.
Final Notes
No injuries were reported among occupants or on the ground. The incident was classified as an "incident" rather than an accident.