What happened
On September 21, 1995, at approximately 16:30 local time, a serious loss of separation occurred near the Hyvinkää gliding site in Finland. An SF340A airliner, registration OH-FAA, operating flight AY-823W from Tampere to Helsinki, passed extremely close to an ASW-19B glider, registration OH-532, while flying through the G 47 airspace.
The airliner was on approach to Helsinki-Vantaa, descending through 3,000 feet, when the crew noticed a glider passing nearby. The vertical separation between the two aircraft was estimated to be between 50 and 150 meters at the moment of near-collision. The pilot of the glider reported hearing the engine of the passing airliner but did not visually identify the aircraft before the encounter. Another glider in the vicinity witnessed the close pass between the two aircraft.
The investigation
The investigation examined the air traffic control (ATC) records, radar data, and radio communications. It was established that earlier that day, a reservation for the G 47 gliding airspace had been granted for altitudes up to 4,000 feet. However, while this reservation was noted on an information board above the radar controller's workstation, the specific map for the G 47 area had not been selected on the radar display terminals.
Investigators also reviewed the communication between the airliner crew and the approach controller. The crew of OH-FAA contacted the controller in Finnish to report the near-miss and inquire about the glider activity limits. The controller, unaware of the active reservation, confirmed the limit was 4,000 feet. The investigation also noted that the primary radar capabilities at Helsinki-Vantaa at the time were insufficient to provide a clear enough target return to allow the controller to identify or warn of unidentified traffic.
Findings
- The primary cause of the incident was a clearance provided to the airliner that led it into reserved glider airspace.
- A breakdown in internal information flow at Helsinki-Vantaa approach meant the radar controller was unaware of the active airspace reservation.
- The controller had not selected the G 47 area on the radar display, and the reservation was not visible on the active radar screens.
- Contributing factors included a high-workload environment during the reservation period and the technical limitations of the primary radar system.
- There was a lack of formal reporting following the event; while the controller logged the incident in the station diary, the aircraft crews and glider pilots did not submit the required official reports to the authorities at the time.