Loss of Directional Control during Landing Roll at Turku Airport on October 25, 2017

On Wednesday October 25, 2017, flight SK4236, a scheduled service from Stockholm, Sweden, to Turku, Finland, was carrying 88 passengers and 4 crew members. The airplane landed at Turku at 2024 h. It did not decelerate as expected. During the landing roll it entered a skid and drifted towards the right edge of the runway with the nose yawed to the left, and eventually impacted runway edge lights. When the airplane was at right angles to the runway heading it was still traveling at 42 kt (78 km/h) groundspeed. It came to a halt approximately 160 m from the runway end adjacent to the runway centerline, having rotated 196° counter-clockwise from the initial direction of travel.

Due to a firm touchdown, weight on the landing gear lightened to such an extent that airplane systems sensed an airborne condition and inhibited the thrust reverser system. A layer of slush over 10 mm deep had accumulated on the runway during a snowfall. The airplane entered a hydroplaning condition upon touchdown. Hydroplaning prevented the wheels from spinning up to a required speed and therefore the anti-skid system did not activate. The captain's brake pedal application, which was later augmented by simultaneous brake application by the first officer, resulted in the wheels remaining locked until the airplane came to a halt.

The flight crew transmitted a mayday call during the skid. Air traffic control notified the emergency response center (ERC) of an accident involving a passenger-carrying airliner and told that the flight crew had indicated there was no apparent damage or injuries. The ERC alerted rescue units to respond to a minor aircraft accident. Paramedic units were not alerted, and the incident commander was not consulted about the matter. The seriousness of the ground-loop was not evident at first, and no damage was initially reported.

There were no injuries. The mainwheel tires exhibited wear and were rendered unserviceable. They also sustained damage by impact with the runway edge lights. The airplane remained at Turku for five days for damage assessment, inspections, and component replacement. Five runway edge lights were broken and had to be replaced.

The single runway 08/26 was notamed closed to air traffic during 2050–2200 h; therefore, the departure of a scheduled flight to Maarianhamina was delayed by over 2 hours.

The Safety Investigation Authority Finland recommends that

• Finavia reviews the current methods for runway condition assessment, runway maintenance, and response to changing conditions, and on the basis of the review implements the necessary changes.

• The Irish Aviation Authority (IAA) oversees that the methods used by CityJet for performance calculations are adequate and ensure safe operation under different circumstances.

• Transport Canada (TC) oversees that Bombardier provides operators with information on the logic of thrust reverser system operation in various situations.

• Transport Canada (TC), as the CRJ series airplane type approval authority, oversees that Bombardier demonstrates that hydroplaning speed are determined in a sufficiently reliable manner for the tire types currently used in airplanes.

• The Ministry of Interior together with the Emergency Response Center Agency investigate ways of finding a modern technical solution that would facilitate quick forwarding of an alarm from an air traffic control facility to an ERC.

Investigation report L2017-05 (pdf, 3.1 Mt)