Accident Overview
A commercial certificated pilot was back-taxiing on a runway in preparation for takeoff and began a 180-degree turn. During the turn, the pilot reported hearing a scraping sound, and the airplane wobbled and shimmied. The right brake was not functioning.
Damage Description
As the turn progressed, the right main landing gear strut collapsed near the axle attach point. The right main wheel and tire separated from the airplane and rolled away. The right wingtip and propeller struck the ground, and the right gear strut was torn loose from its upper attach point.
Post-Accident Examination
A post-accident examination of the right wheel and strut by the airplane owner revealed that the axle assembly had separated from the lower end of the landing gear strut. The axle is secured to the strut by four hex head bolts, each inserted through the axle assembly and gear leg, with a nut threaded and torqued onto the bolt shaft. All four bolts were found bent. Two of the nuts were stripped off their respective bolt shafts, and the remaining two bolts were broken approximately mid-shaft.
Recent Maintenance History
The owner reported that new brake assemblies had been installed on the airplane about five days before the accident. The original bolts were reused during that installation.
NTSB Materials Laboratory Findings
One of the broken bolts was submitted to the National Transportation Safety Board's Materials Laboratory for examination. According to an NTSB materials engineer, the bolt was bent approximately 35 degrees, exhibited necking deformation adjacent to the fracture, and displayed features consistent with an overstress fracture in bending.