What happened
On March 24, 1999, at 17:21 UTC, a serious loss of separation occurred within the Helsinki approach area near Vihti. A Finnair DC-9-51, operating flight FIN 387 from Helsinki to Kajaani, and an Air Express i Norrköping AB Beech 1900 D, operating flight GOT 603 from Norrköping to Helsinki, were on intersecting flight paths without the required vertical separation.
At the time, the approach control center was staffed with several controllers, including trainees working under the supervision of instructors. The Beech 1900 D, registration SE-KXY, was descending through 3,000 feet, while the DC-9-51, registration OH-LYY, was climbing through 4,000 feet. The aircraft were traveling at similar ground speeds of approximately 233–241 knots, with their flight paths intersecting at an angle of roughly 110 degrees.
As the aircraft approached the intersection, the separation between them dropped to a minimum of 2.3 NM, violating the required 3 NM lateral separation. The incident lasted for approximately 20 seconds before the aircraft were successfully repositioned.
The investigation
The investigation examined the actions of the air traffic controllers at the DEP, COR, and ARR workstations, as well as the flight crew of FIN 387. Investigators analyzed radio recordings from Helsinki approach and radar recordings from Tampere area control.
The investigation looked into the communication procedures between the various workstations, noting that controllers relied on verbal shouting due to the close physical proximity of the desks. The investigation also examined the flight crew's actions, specifically regarding a delay in establishing radio contact with the approach controller due to a frequency switching error during a routine task involving anti-icing systems.