ANC17LA022

A fracture and collapse of the main landing gear. Contributing to the accident was corrosion to the hydrasorb lug fitting.

The pilot was landing the airplane on a gravel runway when the right main landing gear collapsed; subsequently, both wings struck the ground. A postaccident examination revealed that the outer radius of the attaching lug on the extension tube that connected the wheel axle to the left main landing gear shock unit was fractured at the shock unit attachment. Visual examination of the fractured lug fitting revealed a flat fracture surface that was perpendicular to the long axis of the fitting, which had extensive evidence of rust and pitting throughout the circumference of the fitting.

On April 29, 2017, about 1600 Alaska daylight time, a Piper PA-18 airplane, N82563, sustained substantial damage when it was involved in an accident in Chugiak, Alaska. The pilot and one passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that upon touchdown on a gravel runway, the right main landing gear collapsed. Subsequently, both wings struck the ground, resulting in substantial damage. The main landing gear were equipped with hydrasorb shock units, which consisted of automotive-type oleo struts combined with light shock cords. The hydrasorb’s outboard end was typically connected to the wheel axle by an extension tube, which was attached to the shock unit by a lug fitting and a through bolt. A postaccident examination of the right main landing gear system revealed that the hydrasorb shock unit’s extension tube lug fitting was fractured through the radius where it would typically be bolted to the hydrasorb’s outboard end. Examination of the broken lug fitting revealed a flat fracture perpendicular to the long axis of the fitting. The fracture surface had evidence of extensive rust and pitting throughout the circumference of the fitting.