What happened
On the evening of August 19, 2000, a LAMCO Eurocub 912 Mk 1 ultralight aircraft, registration OH-U353, experienced a significant flight damage incident during water landing maneuvers near Paraisais, Finland. The pilot was performing practice landings on the water at approximately 21:30 local time.
During the fifth landing attempt, the pilot reduced power at an altitude of approximately 0.5 meters. As the floats made contact with the water, the aircraft suddenly veered to the left and pitched nose-down into the water. An eyewitness observed the right float rotating around its longitudinal axis and bouncing off the surface as the aircraft passed over it. The float detached completely from the airframe and drifted away. While the aircraft's nose initially submerged up to the top of the windshield, it eventually resurfaced. The pilot, who was uninjured, was rescued from the aircraft by nearby vessels.
The investigation
The investigation focused on the structural integrity of the float attachments. Examination of the wreckage at Dragsfjärden revealed that the attachment points for the floats were improperly configured. On the left side, the mounting bolts were loose. On the right side, the primary attachment had failed; a nut and washers had become detached inside the float, and a mounting bracket had snapped.
Investigators found that the installation of the Aerocomp Super Floats 1200 had undergone several different configurations since 1997. The most recent installation used non-locking nuts and relied on marine plywood that was too soft for the high-stress application. The investigation also uncovered discrepancies in the modification documentation provided for airworthiness inspections, which incorrectly stated the number and strength of the bolts used.
Findings
- The primary cause of the right float detachment was the improper attachment of the floats, which allowed a mounting nut to unscrew, leading to the failure of the remaining bracket.
- The attachment utilized soft marine plywood, which allowed the mounting hardware to shift and wear into the wood.
- The installation lacked the use of self-locking nuts, making the assembly susceptible to vibration and movement.
- The structural design of the float struts, made from hardware-store grade aluminum profiles, was insufficient for the operational loads.
- The use of the aircraft's original spring-loaded landing gear prevented the structure from being sufficiently rigid.
- The failure could have been prevented if the attachment points had been inspected more frequently, as significant wear and loosening were visible on the hardware.