What happened
On January 3, 1961, an Aero O/y DC-3, registration OH-LCC, was performing scheduled flight AY-311 from Kruununkylä to Vaasa. The aircraft departed Kruununkylä at 07:16, approximately 11 to 13 minutes behind its scheduled 07:00 departure due to delays in pre-flight preparations.
While approaching Vaasa, the aircraft descended into a forest in the Kirkonkylä area of Koivulahti at approximately 07:40:30. Upon impact, the aircraft caught fire and was completely destroyed. There were 25 fatalities in total, comprising 22 passengers and 3 crew members.
The investigation
The investigation, conducted by a commission appointed by the Ministry of Transport and Public Works, examined the technical condition of the aircraft, the weather conditions, and the flight crew's actions. Investigators analyzed the wreckage, including the engines and propellers, and reviewed radio communications between the aircraft and air traffic control in both Kruununkylä and Vaasa. The investigation also included forensic analysis of fuel samples and structural components, such as the propeller shaft and control column.
Findings
At the time of the accident, weather conditions were deteriorating. While there was radiation fog in the Isokyrö river valley, visibility at Vaasa was approximately 1 km with an 8/8 cloud ceiling at 200 feet.
The investigation identified several contributing factors, but the primary cause was the uncontrolled descent into terrain. The investigation also noted that the aircraft's engines and propellers were within their service intervals, and the aircraft's technical condition was officially rated as airworthy. However, the investigation highlighted concerns regarding the precision of air traffic control instructions and the need for improved weather reporting accuracy to prevent similar occurrences.