What happened
On February 3, 2007, an Ikarus C42B ultralight aircraft, registration OH-U454, was performing its second flight of the day at Pudasjärvi aerodrome when the pilot experienced a sudden change in flight characteristics. During the flight, the front portion of the nose ski attachment housing buckled downward due to aerodynamic pressure. This structural failure created significant drag, causing a noticeable loss of airspeed and a nose-down pitching moment.
Believing the engine had lost power, the pilot executed an emergency landing on an unplowed section of the runway. Upon touchdown, the nose of the ski struck the snow first, causing the nose gear to collapse underneath the aircraft. The plane veered left and came to a stop in a snowdrift with the right wing facing the direction of travel. There were no injuries resulting from the incident.
The investigation
The investigation focused on the structural integrity of the aircraft's landing gear and the cause of the perceived power loss. Investigators examined the nose ski, which had been custom-built by the owner using modified snowboards. The construction consisted of a 7 mm wooden core made of glued slats, covered by 1.5 mm plastic, with an additional 4 mm plastic wear layer and a metal loop.
Technical inspections of the Rotax 912 S engine revealed no mechanical defects or evidence of power loss. The investigation also noted that the pilot reported the damage the following day, rather than immediately after the occurrence.
Findings
- The primary cause of the incident was the failure of the nose ski, which broke at the point where it met the aluminum attachment housing.
- The structural integrity of the ski was compromised by pre-existing holes from previous ski binding screws and a weakened wooden core that had likely suffered damage during prior landings on uneven surfaces.
- The sudden aerodynamic drag caused by the buckling ski led the pilot to misinterpret the situation as an engine failure.
- The subsequent impact with the snow during the emergency landing overloaded the nose gear, resulting in damage to the nose gear, nose ski, propeller, and bent fuselage tubes.