What happened
On October 25, 2017, a CityJet Bombardier CRJ900 operating flight SK4236 from Stockholm to Turku experienced a loss of directional control during its landing roll at Turku Airport. The aircraft, carrying 88 passengers and four crew members, touched down at 12:24 local time. Following touchdown, the aircraft maintained a ground speed of approximately 280 km/h (151 knots), but failed to decelerate as expected.
As the aircraft continued down the runway, it began a gradual lateral drift toward the right side of the pavement. Approximately 1,200 meters after touchdown, the aircraft veered toward the edge of the paved area, striking and breaking five runway edge lights. The aircraft eventually came to a stop approximately 160 meters before the end of the runway, having rotated 196 degrees from its original heading. There were no fatalities or injuries during the event.
The investigation
The investigation examined the aircraft's performance, the runway conditions, and the crew's decision-making processes. Investigators analyzed flight data recorder (FDR) and cockpit voice recorder (CVR) data, as well as radio communications and maintenance records. The inquiry focused on the impact of heavy rainfall on the runway surface, the calculation of landing performance, and the effectiveness of the emergency response and airport maintenance procedures.
Findings
- The primary cause of the excursion was hydroplaning on the runway surface caused by heavy rain.
- The aircraft's landing weight was near its maximum allowable landing weight, which influenced its deceleration capabilities.
- The crew had noted the high crosswind component and the potential for low visibility due to cloud ceilings, but the primary issue was the lack of braking effectiveness on the wet surface.
- The investigation also identified discrepancies in how the emergency call was categorized by the emergency center, which initially classified the event as a minor accident rather than a major aviation accident, affecting the scale of the initial emergency response.
Safety action
- Recommendations were made regarding runway maintenance and the monitoring of friction levels.
- Guidance for calculating performance values was recommended for the operator.
- Improvements to the understanding of engine brake logic and tire hydroplaning speeds were addressed.