What happened
On August 29, 2010, an ultralight aircraft, a FK9 MK IV with registration OH-U482, performed an emergency landing near Ruukki, Finland. The flight, which began at Ahmosuo, proceeded toward Raahe before the pilot experienced engine instability while flying over the Siikajoki river. As the pilot attempted to increase power, the engine failed completely.
The pilot was forced to land in a field, where the aircraft struck a transverse stabilizer during the landing roll. The impact caused the aircraft to flip upside down, resulting in significant damage to the amphibious floats, wings, propeller, engine mount, and the tip of the vertical stabilizer. The pilot, who was flying alone, sustained minor abrasions but no serious injuries.
The investigation
Investigators from OTKES conducted a technical examination of the engine, a Rotax 912 ULS. Upon dismantling the carburetors, they discovered metal shavings at the bottom of the right carburetor float chamber, which had obstructed the main jet. Laboratory analysis of the float shaft pin revealed that a copper and nickel coating had partially delaminated from the steel surface.
The investigation established that the engine manufacturer, BRP-Powertrain Inc, had previously issued Service Bulletin SB-912-048 to address this specific coating issue. The bulletin required the replacement of the old pins with a new version that lacks the copper layer. While the aircraft had undergone a major engine overhaul in 2007, the required modification had not been performed.
Findings
- The engine failure was caused by metal shavings from the float shaft pin delaminating and clogging the main jet.
- The required replacement of the float shaft pin, which was due by December 1, 2005, had been overlooked.
- During a 2007 engine overhaul, the mechanic failed to implement the service bulletin because the carburetors showed no visible defects at that time.
- The maintenance records used a generalized statement claiming all relevant service bulletins had been completed, which masked the fact that this specific modification was still outstanding.
- The aircraft owner holds the ultimate responsibility for monitoring and implementing all necessary service bulletins.