What happened
On April 4, 1997, an MD-83 aircraft, operating as SWW 2082, was performing a direct approach to runway 15 at Kuopio Airport. The flight, arriving from Oulu, contacted Kuopio approach control at 23:49 UTC. After receiving weather information and clearance for a direct approach, the crew acknowledged a QNH of 977.
During the descent, the aircraft began descending through its assigned sector altitude of 2,100 feet. Approximately 18 nautical miles from the touchdown point, the aircraft passed through 2,100 feet and continued to descend to 1,100 feet by the time it reached 15 nautical miles from the runway. The air traffic controller, observing the aircraft's descent on radar, queried the crew regarding their cloud conditions. The crew initially reported they were leaving 2,100 feet, but the controller alerted them that they were actually at 1,100 feet. Upon realizing the error, the crew climbed back to the required 2,100 feet, reaching the altitude approximately 11 nautical miles from the touchdown point. The remainder of the approach proceeded normally.
The investigation
The investigation examined radar data, radio communications, and the airline's standard operating procedures. Investigators noted that while the approach clearance was issued correctly, the crew failed to maintain the assigned sector altitude. The investigation also considered the role of the aircraft's Ground Proximity Warning System (GPWS), though radio transcripts did not confirm that any warnings were heard by the crew. Additionally, the investigation sought a report from the aircraft captain, but no response was received from the operator's headquarters. However, Turkish civil aviation authorities later indicated they had investigated the matter and provided additional training to the captain.
Findings
- The air traffic controller correctly monitored the approach and identified the altitude deviation.
- The crew did not react to the altitude loss, and there was no evidence of a GPWS alert being triggered or acknowledged.
- The primary cause of the incident was the incorrect altimeter pressure setting, which resulted in the aircraft descending below the assigned sector altitude.