What happened
During the takeoff roll of LHQ, a floatplane experienced a structural failure of its front spreader bar. The fracture caused the floats to separate forward of the aircraft's centre of gravity. This sudden shift in weight and geometry caused the aircraft to pitch downward, resulting in the propeller making contact with the water.
The investigation
The investigation focused on the structural integrity of the float assembly and the visibility of potential defects. It was determined that the spreader bar is designed with a portion of the bar housed within a fitting inside the float. This internal placement meant that a specific section of the bar was inaccessible for visual inspection during standard maintenance routines.
In this specific instance, a fatigue crack had developed within that internal, non-visible section of the spreader bar. While the operator had previously identified a fatigue crack on a different aircraft, that crack had extended beyond the float's boundary, making it detectable. The crack in LHQ remained hidden from view until the structural failure occurred.
Findings
- The primary cause of the failure was a fatigue crack located in the internal portion of the spreader bar that could not be visually identified during normal operations.
- The aircraft's operating environment contributed to the structural degradation. The nature of the mission involved frequent, short-duration flights, which increased the number of takeoff and landing cycles per flight hour.
- High levels of taxiing and operating in areas with significant water traffic increased the cyclic loading and mechanical stress placed on the float assembly.