What happened
On 25 June 2003, a float-equipped Cessna A185F, registration OH-CVT, crashed into Lake Ounasjärvi near Hetta, Enontekiö, during a takeoff for a reindeer counting mission. The aircraft, operated by Polar Lento Oy, was attempting to transport two passengers from Lake Ounasjärvi to Lake Kalkujärvi.
The pilot initiated the takeoff heading east into a light three-knot headwind with approximately 10 cm waves. The aircraft was trimmed to lift off the water autonomously. However, once the aircraft reached an altitude of approximately 15 meters, it began to roll and yaw sharply to the right. Despite the pilot applying full opposite aileron and full left rudder, the aircraft could not be corrected and plunged into the water at a near-vertical angle. The aircraft's nose swung more than 90 degrees to the right before the plane capsized and remained afloat on its pontoons.
While the pilot and one passenger escaped with minor injuries, the passenger in the front right seat drowned. The passenger was recovered from the water approximately two hours after the accident.
The investigation
The investigation focused on the pilot's takeoff procedure and the aerodynamic impact of the installed Robertson STOL (R/STOL) kit. This modification mechanically links the ailerons to the flap mechanism; for instance, with flaps set to 20 degrees, the ailerons deflect downward by 13 degrees.
To analyze the airflow, investigators conducted flight tests using a similar aircraft equipped with the same R/STOL kit. Wool yarn strings were attached to the fuselage, vertical stabilizer, rudder, and the upper surface of the right wing to visualize airflow patterns, which were recorded via video.