What happened
On the scheduled route from Helsinki to Mariehamn via Turku, the aircraft departed Turku at 16:20 GMT. The flight was operating with a crew of three and 21 passengers, though an unauthorized individual—a former pilot—was also present in the cockpit. During the leg toward Mariehamn, the aircraft type maintained an altitude of approximately 2,000 feet without any reported irregularities.
As the flight approached the Mariehamn NDB (MAR) from the east-northeast, it was positioned on the inbound track for runway 20. At 16:57 hours, the aircraft passed over the NDB. While maintaining its inbound course during the final approach, the plane struck a line of trees roughly 1,470 meters from the runway threshold while flying in a nearly horizontal orientation. The impact caused the aircraft to roll onto its back and immediately ignite. The accident occurred at 16:59 hours, resulting in 22 fatalities and leaving one crew member and two passengers with serious injuries.
Findings
Investigations into the crash focused on the pilot's perception of the flight's altitude. It was determined that the primary factor was a malfunctioning altimeter in the cockpit of the pilot-in-command. This equipment defect provided an incorrect altitude reading, which led the pilot to fly below the minimum safe altitude required for the weather conditions present during the instrument approach to runway 20.