Aero Flight 311 (AY311), often referred to as the Koivulahti air disaster, was a scheduled domestic passenger flight operated by Aero O/Y (now Finnair) between Kronoby (Finnish: Kruunupyy), Finland and Vaasa. The aircraft, a Douglas DC-3C, crashed near Kvevlax (Finnish: Koivulahti) on January 3, 1961, killing all twenty-five people on board. The disaster remains the deadliest civilian aviation accident in the history of Finland.