Cessna 180 N6479X accident near Naknek, Alaska

Probable cause

The overstress fracture and subsequent separation of the left main landing gear axle due to a hard landing, which resulted in the pilot’s inability to maintain directional control of the airplane.

NTSB analysis

The commercial pilot stated that, during the landing rollout in the tailwheel-equipped airplane, the left wheel axle fractured and separated from the airplane with the wheel attached. The left landing gear leg then dug into the runway surface, the airplane made a sudden left turn, and the left wing and left horizontal stabilizer struck the runway.

An examination of the fractured left axle revealed features consistent with a bending overstress fracture. High magnification optical examination of the fracture also revealed several small fatigue cracks within the crack origin area. Although several fatigue initiation sites were present along the fracture origin area, none of them were large enough to have led to the failure or to have significantly lowered the ultimate strength of the axle enough for a bending overstress failure to occur under normal loading conditions. Therefore, it is likely the landing gear axle failed as a result of bending overstress due to a hard landing.

Text from the NTSB. Open the NTSB docket for ANC16LA024 for the full record.