What happened
On September 17, 1996, a serious loss of separation occurred near Halli Airport involving two aircraft operating on different radio frequencies. A McDonnell Douglas F-18 Hornet, registration HN-461, was performing an automated ILS approach to runway 26 as part of a flight test. Simultaneously, an experimental RV-4, registration OH-XKD, departed from runway 08 on a VFR flight plan toward Pori.
As the F-18 Hornet continued its approach, the RV-4 climbed and began a turn over Eväjärvi. The two aircraft passed each other near the end of runway 26 with a vertical separation of approximately 100 meters. The pilot of the OH-XKD noticed the jet engine noise and subsequently gained visual contact with the climbing military aircraft, which was positioned in the front sector of the experimental plane. The air traffic controller observed the close encounter and issued a collision warning alert.
The investigation
The investigation examined radio communications, flight data from the F-18 Hornet, and controller statements. It was established that the air traffic controller was managing traffic based on assumptions rather than verified position data. The investigation noted that while the controller attempted to provide flexibility for the flight test, this led to a failure in maintaining proper separation and providing necessary traffic information. The investigation also highlighted that the controller lacked real-time radar monitoring capabilities for the specific area of the incident and relied heavily on visual observations and personal assumptions regarding the aircraft's trajectories.
Findings
- The primary cause of the near-collision was that the air traffic controller formed a mental picture of the traffic based on assumptions rather than verified information.
- The controller did not have accurate position data for the F-18 Hornet at the time the departure clearance was issued to the OH-XKD on the opposing runway.
- The controller failed to provide necessary traffic advisories to the pilots, which was particularly critical as the aircraft were operating on different radio frequencies.
- The flight test clearance provided to the F-18 Hornet did not align with the actual operational requirements, leading to a lack of mandatory position reporting.
- The use of opposing runways contributed to the risk, although it was deemed necessary for the ILS approach requirements.