Cessna 402C N522FA incident near Fort Lauderdale, Florida

Probable cause

The airplane manufacturer's inadequate inspection procedure resulting in undetected fatigue cracking of the main landing gear barrel of the upper barrel and trunnion assembly.

NTSB analysis

During landing an undetected fatigue crack in the barrel of the left main landing gear upper barrel and trunnion assembly, which penetrated to approximately 70 percent of the wall thickness, resulted in complete fracture of the upper barrel and subsequent separation of left main gear assembly. The airplane departed the left side of the runway and came to rest on the grass. The fatigue origin was on the outer diameter surface, and propagated radially inward with little or no circumferential propagation. The fracture was located in a transition zone of the barrel where the radius did not meet the specification. Additionally, measurements of the inside and outside diameters of the barrel revealed out of tolerance dimensions. The barrel material, heat treatment, and hardness were consistent with the specifications for the part, while the surface finish was less than the specified value. An area of the barrel immediately beneath the fracture surface exhibited smooth areas with corrosion pits. Moderate corrosion was also noted at the upper edge of the side brace collar following paint removal by chemical and mechanical means. The only inspection of the barrel specified by the airplane manufacture is a visual inspection checking for corrosion, pitting, and cleanliness. No other inspection requirements are stipulated for the fracture area of the upper barrel and trunnion assembly. The last visual inspection was performed approximately 58 flight hours before the incident. The Safety Board has investigated 2 previous accidents in which the upper barrel and trunnion assembly fractured. In both previous cases, the barrel fractured above the side brace collar.

Text from the NTSB. Open the NTSB docket for ERA09IA115 for the full record.