What happened
On the evening of October 25, 2017, a Bombardier CRJ900 operating as SAS flight SK4236 arrived at Turku Airport from Stockholm, Sweden. The aircraft, carrying 88 passengers and 4 crew members, touched down on runway 26 at 20:24 local time.
Upon touchdown, the aircraft maintained a groundspeed of approximately 151 knots but failed to decelerate as expected. During the landing roll, the aircraft entered a skid, causing the nose to swing left while the aircraft began drifting toward the right edge of the runway. Approximately 1,200 meters from the touchdown point, the aircraft veered toward the paved edge, striking and breaking five runway edge lights. The aircraft continued to rotate, eventually coming to a halt 2,050 meters from the initial touchdown point, having rotated 196 degrees from its original heading. The final position was roughly 160 meters from the runway end.
The investigation
The investigation examined the environmental conditions, aircraft systems, and operational procedures. Investigators analyzed flight data recorder information, cockpit voice recordings, and radio communications. The inquiry focused on the effectiveness of aerodrome maintenance, the aircraft's anti-skid and thrust reverser systems, and the crew's performance calculations. The investigation also reviewed the emergency response and the accuracy of the initial accident classification by the emergency dispatch center.
Findings
- The aircraft experienced hydroplaning during the landing roll, which prevented effective deceleration.
- There were discrepancies in the calculation of landing performance, specifically regarding the use of maximum landing weight and runway friction conditions.
- The aircraft's thrust reverser system logic and its impact on directional control were scrutinized.
- The emergency response was complicated by ambiguous communication, leading the dispatcher to initially classify the event as a minor accident rather than a major one.
Safety action
- Recommendations were made regarding runway maintenance and the implementation of the Global Reporting Format (GRF).
- The investigation highlighted the need for improved guidance on performance calculations for operators.
- There is a need for enhanced training regarding the operating logic of thrust reverser systems and the risks of tire hydroplaning.
- Improvements to the processing of aircraft accident alerts in emergency response centers were suggested to ensure more accurate initial classifications.