Amateur-built RV-4 N66PB accident near Arlington, Washington

Probable cause

The failure of both main landing gear's drag link bolts in overstress and the subsequent collapse of the landing gear during landing rollout.

NTSB analysis

The pilot said that when he took off and retracted the airplane's landing gear, only the tailwheel retracted. He lowered the landing gear and saw three green lights, indicating that all three landing gear were down and safe for landing. He then proceeded to his destination with the main landing gear down. During landing rollout at his destination, the left main landing gear collapsed. The airplane departed the left side of the runway before the right main landing gear collapsed as well. When the left wing's main landing gear collapsed outward, it damaged the wing structure and punctured the left fuel tank. The skin on the top of the right wing and the right aileron were wrinkled. Postaccident examination of the landing gear revealed that both main landing gear drag link bolts failed. These bolts were welded to the back of each main landing gear as part of their landing retraction system. Examination of photographs of the broken bolts by an NTSB metallurgist revealed that each bolt exhibited cantilever beam bending in overstress. The quality of the photographs was inadequate to determine if fatigue played a role.

Text from the NTSB. Open the NTSB docket for WPR10LA171 for the full record.