What happened
On a day flight from Stony Rapids, Saskatchewan, a Northern Dene Airways Ltd. Metro III, registration C-FIPW, was carrying two crew members and nine passengers to La Rongend, Saskatchewan. Upon arriving at La Ronge at approximately 1410 CST, the crew performed standard landing procedures. The aircraft touched down approximately 1000 feet from the threshold of Runway 18 during a crosswind landing.
Immediately following touchdown, the left wing dropped, causing the propeller to strike the runway. The aircraft veered left despite maximum control inputs from the crew. As the aircraft traveled through the infield, the nose and right main landing gear were torn rearwards, while the left gear collapsed into the wheel well. The aircraft slid on its belly for about 300 feet before coming to a stop. While the pilots and most passengers were unhurt, three passengers sustained minor injuries due to the sudden impact of the gear collapse.
The investigation
Investigators examined the aircraft's landing gear mechanism, which utilizes a three-piece drag brace held in a locked position by positioning cams and bellcrank rollers. Post-accident inspections revealed that the left main landing gear's outboard roller was the incorrect part; it was a smaller diameter bearing intended for use as an uplock roller rather than the required component. This undersized roller reduced the necessary rigging clearance.
Furthermore, the inboard bellcrank-to-cam assembly was found to be out of adjustment. The investigation also identified a bald spot on the left outboard tire, consistent with the smoke observed during touchdown. The physical evidence suggested that the mechanical loads of the landing were sufficient to overcome the remaining spring tension, causing the gear to move beyond its locking limit.
Findings
- An aircraft maintenance engineer installed an incorrect, undersized roller on the left main landing gear outboard bellcrank assembly.
- The use of the smaller diameter roller reduced the required rigging tolerances, allowing the assembly to eventually move beyond the positioning cam cutout.
- A necessary rigging check was not performed following the part installation, which would have identified that the assembly failed to meet minimum requirements.
- The firm landing in a crosswind provided the side loading necessary to cause the gear to collapse.