What happened
On April 29, 2003, at 10:42 local time, a separation loss occurred in the Kuopio terminal area involving a Finnair ATR 72-201 (call sign FIN503) and a pair of Finnish Air Force Hawk Mk 51 jets (call/callsign J11 and J12).
At the time, the approach controller had decided to use runway 33 for the arrival of FIN503, despite runway 15 being the active runway for departures. The Hawk pair was cleared to take off from runway 15, with instructions to turn left toward the northeast after takeoff to maintain an altitude of 550 meters. Simultaneously, the ATR 72-201 was vectored to the left base leg for runway 33 and cleared to descend to 2100 feet.
The two aircraft flew without required separation for approximately 8 seconds. During this period, the minimum horizontal distance between them was 4.6 km, and the minimum vertical distance was 180 meters. The pilots of FIN503 received a TCAS Traffic Advisory (TA) indicating another aircraft was approximately 500 feet below them, though no visual contact was established.
The investigation
The investigation examined the actions of the approach and tower controllers, the flight paths of the involved aircraft, and the coordination between air traffic services. The investigation established that the Hawk jets took off individually with 20-second intervals. The approach controller observed on radar that the lead Hawk (J11) was continuing straight along the runway 15 centerline longer than anticipated, creating a risk of conflict with the arriving ATR 72-201.
To resolve the conflict, the controller ordered FIN503 to maintain 3100 feet and perform a right-hand orbit. However, the investigation found that the aircraft had already descended below the target altitude by the time the instruction was received.
Findings
- The primary cause of the incident was that the approach controller abandoned vertical separation between FIN503 and J11 without ensuring horizontal separation was maintained.
- The controller attempted to manage the conflict by changing the arrival altitude of the commercial aircraft but failed to verify that the departing military aircraft had cleared the arrival path.
- The controller's decision to use runway 33 for the arrival, while different from the active runway 15, contributed to the complexity of the traffic situation.
- The Hawk lead aircraft continued on the runway 15 heading longer than expected, which led to the loss of separation.
- The pilots of both aircraft operated in accordance with their assigned clearances.