B4/2004L Aviation accident in Äkäslompolo, Kolari on 19 September 2004

On Sunday, September 19, 2004 at approximately 17:36 hours an aviation accident occurred on lake Äkäslompolojärvi in Kolari in which a Lake LA-4-200 Mod. “Buccaneer”-type amphibian aircraft OH-AKF owned by a private person crashed into lake Äkäslompolojärvi while on a cross-country flight. The aircraft was completely destroyed in the impact and sank to a depth of 10 meters down in a few minutes. The two persons in the aircraft were killed. On September 24, 2004 in its decision B 4/2004 L the Accident Investigation Board Finland appointed an investigation committee with investigator Pekka Alaraudanjoki named as chairman, and investigators Matti Korjula, Sippo Nevalainen and Juhani Mäkelä as members.

The aircraft involved in the accident departed off the Rauhala village side of lake Jerisjärvi, from where the men intended to fly near Rovaniemi to Ylikylä and land on the river Ounasjoki nearby. On the left in the pilot's seat was a person whose license was no longer current and in the neighbouring seat, the owner of the plane who was in possession of a current license. The plane was equipped with dual controls. Due to the poor weather they had flown low, at an altitude of approximately 50 - 100 meters, following the shoreline of the river Äkäsjoki leading south from lake Jerisjärvi. The men's plan was apparently to fly via lake Äkäslompolojärvi, from where they would pass through the ravine between Yllästunturi and Kesäkitunturi fjeld into an area of lower-lying terrain, and from there on to the river Ounasjoki and the final destination, Ylikylä.

The aircraft reached the north shore of lake Äkäslompolojärvi near cruising speed at an altitude of approximately 30 - 50 meters. Close to the shore the upper ear of the left horizontal stabilizer's rear attachment fitting broke completely off as a result of fatigue. Subsequently, the stabilizer twisted downward whereupon the forward attachment ear also broke due to the force of the air stream. The stabilizer remained attached to the airplane only by the lower ear of the rear attachment fitting. As a result of the damage the pilot was unable to control the aircraft and it crashed into the lake, canted to the right. The right wing tip struck the water’s surface first, causing the aircraft to be flung to the left, with the left wing and forward fuselage taking the largest force of impact. Both occupants sank along with the plane to a depth of approximately ten meters and perished by drowning.

Subsequent inspections revealed that neither the weather nor the crew had a direct effect on the origin of the accident. The upper ear of the left horizontal stabilizer’s attachment fitting had been subjected over a relatively prolonged period to forces exceeding the material's fatigue tolerance and failure had ensued. In the inspections no indications were found that the attachment ear had been entirely broken for long. When final breakage of the attachment point occurred, the surface area of the horizontal surface remaining intact was small. No indications were found that the damaged surfaces had chafed together. This points to the conclusion that after the final breakage of the attachment ear, the stabilizer, due to the effect of the air stream, also broke loose from the forward ear which had been weakened from prior vibration. The air stream then bent the stabilizer downward, whereupon the elevator trim torque tube twisted off and the structure joining the elevators was torn. At that time the aircraft’s vertical control capability was almost completely lost.

The cause of the accident was fatigue breakage of the upper ear of the left horizontal stabilizer’s rear attachment fitting which, as it progressed, finally led to breakage of the entire attachment point, whereupon the stabilizer was able to twist downward. At that time control of the aircraft was lost and it crashed into the lake.

On October 7, 2004 the investigating committee informed the Finnish Civil Aviation Administration’s Flight Safety Authority of its findings and of the stabilizer attachment ear breakage. Because in following current aircraft maintenance and inspection directives it is nearly impossible to detect an incipient fatigue fracture in an attachment point, the investigating committee recommends that the authorized aviation authority undertake measures to ensure the reliability of stabilizer attachments.

B4/2004L Report (pdf, 1.28 Mt)