Event Description
Following a smooth landing and rollout, the pilot observed a change in the airplane's attitude as the nose pitched down. The nose gear then collapsed, causing the aircraft to slide to a stop in an upright position. The aircraft incurred substantial damage to the fuselage structure at the connection point of the nose gear drag link to the casting. Impact with the runway surface also damaged the lower front cowling and the propeller blades.
Examination Findings
The nose gear yoke and nose gear strut assemblies were sent to the NTSB Materials Laboratory Division for examination. The examination indicated that the nose gear failed in overstress, consistent with the nose gear yoke moving aft and to the right relative to the nose gear strut. Reports stated that incorrect nose gear yoke attachment bolts and nuts were installed incorrectly, and one of the bolts was fractured, consistent with overstress in shear. Additionally, a wedge-shaped spacer was missing from between the nose gear strut and the nose gear yoke, which would affect the loading of the four yoke attachment bolts. Various cracks were also noted around the attachment bolt through holes, and the fracture surfaces were consistent with fatigue.
Cause
The investigation determined that the failure was due to incorrect installation of nose gear yoke attachment bolts and nuts, the absence of the required wedge-shaped spacer, and the presence of fatigue cracks around the attachment bolt through holes, leading to overstress failure.