What happened
On the early morning of 7 January 2019, a Saab 340B aircraft, registration not specified, was performing a positioning flight from Riga to Savonlinna. The flight, operated by RAF-AVIA, was intended to ferry the aircraft to the airport for scheduled services following the holiday period.
During the approach, the flight crew arrived earlier than anticipated due to favorable winds. At the time of the arrival, the airport was in the midst of winter maintenance. Although runway clearance vehicles had been active since the early morning, new snow continued to fall. While the runway was reported to be free of ice, significant snow accumulation was present at the edges.
As the aircraft approached for landing, the runway friction measurements indicated poor conditions, with values ranging from medium to poor. During the landing roll, the aircraft veered off the runway centerline, resulting in the aircraft leaving the paved surface.
The investigation
The investigation examined the sequence of events, the effectiveness of the airport's winter maintenance, and the communication between the flight crew and the airfield flight information service (AFIS). Investigators analyzed flight data recordings, cockpit voice recordings, and the maintenance logs of the airport. The inquiry also looked into the friction measuring results obtained shortly before the aircraft's arrival and the state of the runway surface, which featured a 4 mm layer of dry snow and snowbanks encroaching upon the cleared width of the runway.
Findings
- The runway friction was measured as poor across the landing surface immediately prior to the arrival of the aircraft.
- The cleared width of the runway had been reduced to 37 metres due to the presence of snowbanks located four metres inside the runway edge lights.
- A layer of dry snow covered the entire cleared area of the runway.
- There was a lack of clear communication regarding the specific reduced width of the cleared runway and the presence of encroaching snowbanks to the flight crew.