A potential major aviation accident - Investigation completed on loss of directional control during landing roll at Turku Airport on October 25, 2017

Safety Investigation Authority Finland (SIAF) has completed an investigation into the loss of directional control of an airliner on landing at Turku Airport on October 25, 2017. The airplane, arriving from Stockholm, did not decelerate as expected and entered a skid, with the nose pointing slightly to the left of track. It continued to drift toward the right edge of the runway and impacted runway edge flights. The skid developed until the airplane was at right angles to the runway heading, at which point it was still traveling at 78 km/h groundspeed. It came to a halt approximately 160 m from the runway end adjacent to the runway centerline, having rotated 196° counterclockwise from the initial direction of travel. The air temperature was around freezing and the runway was covered with slush over 10 mm deep. High gusting wind was blowing from the southeast.

The occurrence did not result in injuries to the four crew members and 88 passengers. The flight crew transmitted a mayday call while the airplane was skidding along the runway. The occurrence had potential for a serious or major accident. SIAF issues four safety recommendations with the aim of preventing similar occurrences and improving aviation safety.

SIAF 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.

Information on runway conditions as received by a flight crew may differ considerably from the actual landing conditions when weather is changing rapidly. During the investigated occurrence, the thickness of the slush deposit was clearly on the increase, but this information was not passed on and the runway was not cleared.

SIAF also recommends that the Irish Aviation Authority (IAA) oversees that the methods used by CityJet for performance calculations are adequate and ensure safe operation under different circumstances. The investigation showed that the company tables used for performance calculations are complex and not easily deciphered. The importance of accurate performance calculations and skills acquired through training is accentuated in winter conditions.

In addition, SIAF recommends that Transport Canada (TC) oversees that Bombardier provides operators with information on the logic of thrust reverser system operation in various situations. The thrust reverser system on the CRJ900 is inhibited when it is selected in flight. If reverse thrust is selected prematurely during landing it cannot be regained without specific flight crew actions.

SIAF furthermore recommends that TC, as the 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 risk of hydroplaning sometimes goes unnoticed or is not recognized owing to the fact that runway deposits are usually rather thin. The currently observed hydroplaning speeds are often calculated using an equation that does not necessarily correlate with the modern aircraft tires. The effects of slush and other deposits than water on hydroplaning speeds shall also be examined.

Finally, SIAF recommends that the Ministry of Interior together with the Emergency Response Center Agency investigate ways of finding modern technical solutions that would facilitate quick forwarding of an alarm from an air traffic control (ATC) facility to an emergency response center (ERC).

Since an automatic alerting system is not installed, Turku ATC will need to alert the ERC by telephone. An air traffic controller cannot digress from controlling duties for the duration of an emergency call. This will lengthen the processing time of an alarm and delay its dissemination. The ERC also underestimated the accident potential of the occurrence. This assessment was made at the ERC where the occurrence was classified as a minor aircraft accident. Paramedic units were not alerted, and the incident commander was not consulted on the matter without consulting the incident commander about the matter.

Safety Investigation Report.

More information:
Ismo Aaltonen, Chief Air Safety Investigator, tel. + 358 (0) 295 150 703
Veli-Pekka Nurmi, Executive Director, tel. + 358 (0) 295 150 701