Cessna 172S N137RJ accident near La Verne, California

Probable cause

The failure of the right main landing gear tubular spring due to a fatigue crack that originated at the airframe connecting bolt hole and progressed to an overstress fracture.

NTSB analysis

During the takeoff roll for a simulated short-field takeoff, the right main landing gear wheel did not immediately rotate, and the right main landing gear leg subsequently collapsed.

Postaccident examination found that the right main landing gear tubular spring had separated near its inboard end, with the tip of the fracture about 4 inches outboard of the airframe connecting bolt hole. Further examination revealed a spiraling crack that traveled inboard from the tip of the teardrop-shaped fracture surface to the connecting bolt hole and extended through the wall thickness at the bolt hole. Multiple areas of fatigue were identified on the fracture surface of the smaller inboard piece. The fatigue emanated from the outer diameter corner of the connecting bolt hole and was consistent with fatigue occurring over a long period of time. Some features on the fracture surface were consistent with fast fracture due to overstress, and galling was observed in rub damage consistent with metal-to-metal contact during movement between the hole surface and the outer diameter of the mating connecting pin.

The spiraling crack was visible when viewing the tubular spring through the cabin floor inspection hole positioned directly above the fracture. Although the crack was possibly present but went unobserved during previous 100-hr or annual inspections, the investigation was unable to identify when the cracking in the visible area began.

Text from the NTSB. Open the NTSB docket for WPR25LA102 for the full record.