What happened
On November 19, 1998, at approximately 17:55 local time, a serious loss of separation occurred near the Rengo reporting point in Finland. Two aircraft, a Finnair DC-9-51 (registration OH-LYZ) and an Air Botnia SAAB SF340A (registration OH-SAC), passed each other on opposing tracks. The incident involved a total of 81 people on board both aircraft.
At the time of the event, the DC-9-51 was operating a scheduled flight from Vaasa to Helsinki, while the SAAB SF340A was operating a flight from Helsinki to Vaasa. The aircraft passed each other with a vertical separation of approximately 600–700 feet and a lateral separation of about 1 nautical mile, violating both vertical and lateral separation minimums.
The investigation
The investigation examined radar data from the Southern Finland Approach Control, as well as telephone and radio communications between Tampere-Pirkkala Approach, Helsinki Approach, and Tampere Area Control (ACC).
Investigators reviewed the sequence of instructions provided by ACC to the various approach units. They specifically looked at how altitude restrictions were communicated and recorded on the flight strips used by the radar controllers. The investigation also analyzed the radio transcripts between the flight crews and Helsinki Approach to determine why the DC-9-51 failed to maintain the required altitude initially.