Accident Overview
On November 27, 2010, at 1030 Pacific standard time, an American Champion 7KCAB tailwheel-equipped airplane, registration N5101X, sustained substantial damage to the fuselage and left wing assembly following a main gear collapse during landing at Rialto Municipal Airport, Rialto, California. The certified flight instructor (CFI) and the private pilot receiving tail wheel instruction were not injured. The airplane was operated by Foothill Flying Club as a visual flight rules (VFR) instructional flight under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed; no flight plan was filed. The flight originated from Upland, California, at 0930.
Pilot Report
According to the CFI's written report to the National Transportation Safety Board (NTSB) investigator-in-charge, during a wheel landing with the private pilot manipulating the flight controls, the airplane's left main landing gear collapsed. The airplane skidded to the left and contacted a taxiway sign before coming to rest. The instructor reported calm wind conditions at the time of the accident.
Examination of the Landing Gear
The fractured landing gear leg was sent to the NTSB Materials Laboratory in Washington, D.C., for further examination. An NTSB senior metallurgist reported that the left landing gear leg fractured at the inboard end, approximately where the spring passes through the fillet plate and seal. The inboard fracture face exhibited a dark crescent-shaped region on the aft edge, with a smooth dark appearance, a crack arrest mark, and ratchet marks consistent with fatigue cracking from multiple origins. The remainder of the fracture face showed a coarse, grainy appearance with clear chevron markings adjacent to the fatigue crack and a shear lip, consistent with overstress fracture. The paint on the underside of the spring had worn away in the region of the fracture, where support wedges contact the surface. Corrosion damage was present on the worn surfaces.