What happened
On June 30, 1999, at approximately 09:04 UTC, two Finnair aircraft operating in opposite directions experienced a loss of separation near the Renko reporting point. The first aircraft, an ATR 72-210 with registration OH-KRL (callsign FIN 343), departed Helsinki for Kokkola. The second aircraft, a DC-9-51 with registration OH-LYR (callsign FIN 268), departed Tampere for Helsinki.
As the aircraft approached each other, the required vertical separation was not maintained. The ATR 72-210 was climbing through flight level 129, while the DC-9-51 was descending through flight level 128. At the moment of minimum separation, the aircraft were approximately 2.4 NM apart with a vertical difference of only 300 ft. The minimum required horizontal separation in this airspace is 5 NM.
The investigation
The investigation examined the coordination between Tampere Area Control and the Helsinki and Pirkkala Approach control units. Investigators reviewed radio communications and telephone recordings between the controllers. The investigation established that the controllers were aware of the potential conflict and attempted to implement altitude and heading changes to maintain separation. However, a critical moment occurred when a controller attempting to contact the area control desk was unable to communicate effectively because the person answering the telephone hung up the line too quickly during simultaneous radio traffic.
Findings
- The primary cause of the incident was the failure to maintain required vertical and horizontal separation between the two aircraft.
- Coordination between the different control sectors was hindered by communication difficulties, specifically a brief interruption in telephone contact between the approach controller and the area control desk.
- The DC-9-51 was not equipped with a Traffic Collision Avoidance System (TCAS), whereas the ATR 72-210 was.