What happened
Shortly after departing from a private dock on Trout Lake, Ontario, a Cessna 180G experienced a sudden, uncommanded roll and began a steep descent. The aircraft, registration N4695U, struck rising terrain at approximately 0840 Central Daylight Time. The impact resulted in two serious injuries and one minor injury. While the pilot and front passenger were wearing seatbelts, the rear passenger was unrestrained. Following the crash, the aircraft sustained significant damage, though no post-crash fire occurred. The accident site was only accessible by water, and the occupants were eventually located by local residents arriving by boat.
The investigation
Investigators examined the wreckage and found that a clevis pin, which secured a front bracing wire to the left landing-gear adapter, was missing. It appears the pin was not secured by a cotter key, allowing it to fall out of the clevis fork shortly after takeoff. This disconnection caused the float bracing wire to detach.
Further examination of the float attachment fittings revealed evidence of polishing and fretting, suggesting that looseness and free play had developed in the components over time. Additionally, investigators noted internal corrosion on the spreader bars that was not visible from the exterior. The investigation also noted that the aircraft's weight was slightly above its maximum allowable gross takeoff weight, though a discrepancy in the empty weight records suggested the actual weight may have been lower than documented.
Findings
- The primary cause of the accident was the disconnection of the front bracing wire due to an unsecured clevis pin.
- Pre-existing looseness in the float attachment fittings allowed the floats to twist out of alignment once the wire disconnected.
- The resulting misalignment increased both induced and parasitic drag, leading to a loss of airspeed and an aerodynamic stall.
- The stall occurred at an altitude of approximately 200 feet above the treetops, leaving the pilot with insufficient height to recover the aircraft.