What happened
On July 9, 2015, a Boeing 737-800 performing a flight from Chania (LGSA) to Copenhagen (EKCH) entered the Warsaw FIR without establishing radio contact with air traffic services. Controllers at ACC Bratislava and ACC Warsaw attempted to contact the crew multiple times on the international emergency frequency (121.5 MHz) without success.
To manage the situation, air traffic controllers had to adjust the altitude of another aircraft within the sector to maintain increased vertical separation due to the unpredictable nature of the non-responsive flight. In an effort to re-establish contact, another crew from the same airline was utilized to attempt communication via the company traffic frequency and through ACARS messaging. The crew of the Boeing 737-800 eventually established contact near the POLON waypoint, after being prompted by the other airline aircraft on 121.5 MHz.
The investigation
The PKBWL coordinated with the Accident Investigation Board Norway to gather detailed information regarding the event. The investigation included statements from the captain of the aircraft involved.
According to the pilot, both members of the flight crew were awake and wearing headsets during the cruise phase. While the 121.5 MHz frequency was tuned, the crew noted that the ACARS system was not communicating at that time, which explains why they did not receive the initial alerts. The crew reported that the communication from the company aircraft was clear, but they could not provide a technical reason for the preceding period of silence.
Findings
- The crew was monitoring the emergency frequency, yet communication with Warsaw ATC was not established.
- The ACARS system was non-functional for incoming messages during the period of lost contact.
- The exact cause of the radio communication failure remains undetermined.