What happened
On September 12, 1996, a serious loss of separation risk occurred in airway W3, south of Vaasa, Finland. During the 'Janne-96' military exercise, a flight of three Saab J35F Draken aircraft (registration DK-241, DK-243, and DK-255) departed from the Halli airbase for a combat training mission.
While operating at altitudes between 3,000 and 3,500 meters, the military formation crossed the western boundary of their assigned training area and entered airway W3. At the same time, two civilian aircraft were utilizing the same airway: an Air Botnia Jetstream 3201 (OH-JAE) flying from Oulu to Turku, and a Cessna 402B (OH-CHS) flying from Seinäjoki to Helsinki.
At approximately 11:10 local time, a combat controller in Kauhavan noticed the military formation had exited the training area. However, the combat controller at the Halli base, relying on a radar display with a limited 160 km range, believed the airway was clear because the aircraft had moved beyond his radar's technical coverage. The military formation eventually crossed back into the training area, but not before passing through the active airway where the civilian aircraft were operating. The pilots of the civilian aircraft did not observe the military formation, though the crew of OH-JAE reported seeing two aircraft flying below them approximately 20–30 km ahead.
The investigation
The investigation examined the radar coverage, radio communications, and the coordination between military combat controllers and civilian air traffic controllers. Investigators found that the Halli-based combat controller was operating with a restricted radar view that could not display targets beyond 160 km. Because the military formation was flying under a non-standard pressure setting (QFE 986 hHDa), the secondary surveillance radar failed to transmit altitude information (C-mode) to the controller's display.
Furthermore, the investigation looked into the command structure, noting that the operation was led by a reserve combat controller in a manner that deviated from established guidelines. The investigation also reviewed the responses of the air traffic controllers, who initially sought to verify the situation through inquiries rather than issuing immediate corrective instructions or traffic advisories to the aircraft involved.