What happened
On December 30, 1997, at approximately 00:12 local time, a Scandinavian Airlines System (SAS) DC-9-41, registration LN-RLT, experienced a runway excursion while landing at Turku Airport. The flight, operating as SK-720 from Stockholm Arlanda, was carrying 27 passengers and a crew of four.
During the ILS approach to runway 26, the captain elected to use an approach speed of 130 knots, slightly above the calculated 125 knots, believing the aircraft would stop within the 2500-meter runway length despite the slippery conditions. As the aircraft touched down, the runway surface was covered with 2 mm of slush, and recent friction measurements indicated moderate braking effectiveness.
During the landing roll, the aircraft drifted toward the edge of the runway. The right main gear traveled onto the grass, and the aircraft eventually exited the paved surface, traveling approximately 550 meters alongside the runway edge. While the left main gear and nose gear remained on the paved portion, the aircraft encountered a 15-20 cm snowbank. The aircraft eventually came to a stop 1800 meters past the runway threshold. There were no injuries to the passengers or crew, though the aircraft sustained minor damage.
The investigation
The investigation examined the aircraft's flight data, cockpit voice recordings, and meteorological conditions. Investigators reviewed the pilot's decision-making regarding approach speed and the impact of environmental factors. The inquiry also scrutinized the actions of the air traffic controller at Turku Tower, specifically regarding the notification of emergency services and the management of the incident following the excursion.
Findings
- The primary cause of the excursion was the captain's incorrect perception of the aircraft's lateral movement during the final approach and landing phase.
- This misperception was exacerbated by the use of high-intensity approach lights in a manner contrary to established procedures, combined with snow drifting across the runway due to crosswinds.
- Contributing factors included the absence of runway centerline lights and the presence of snow covering runway markings, which obscured visual cues.
- The monitoring pilot, who was a trainee with limited experience, found it difficult to intervene and correct the situation.
- The investigation also noted failures in ground procedures, including the air traffic controller's failure to immediately notify rescue services, the police, or the accident investigation authority, and a failure to promptly issue a NOTAM regarding the runway closure.