WPR10LA221

The certificated flight instructor (CFI) stated that, during the instructional flight, the pilot receiving instruction was practicing three-point landings in preparation for his tailwheel endorsement. The first landing was harder than normal due to a higher-than-normal sink rate. During the next landing attempt, the airplane yawed to the left. The CFI took over the airplane controls and corrected toward the runway centerline. While correcting, he heard a loud snapping noise followed by a loud scraping noise and felt the airplane make a sudden left turn. Postaccident examination revealed that the left landing gear strut fractured at the inboard end. Examination of the landing gear fracture surface by an NTSB materials laboratory metallurgist revealed evidence of fatigue cracking, an overstress fracture, and corrosion damage.

On April 30, 2010, at 1250 Pacific daylight time, a Cessna 170A, N5765C sustained substantial damage following a left main landing gear collapse, during landing at the Minden-Tahoe Airport, Minden, Nevada. The airplane was registered to a private party and operated by the pilot under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The certificated flight instructor and pilot receiving instruction were not injured. The instructional flight departed Carson, Nevada at 1130 with a planned destination of Minden-Tahoe. Visual meteorological conditions prevailed, and no flight plan had been activated for the visual flight rules (VFR) flight. The certificated flight instructor (CFI) stated that the purpose of the flight was to practice for a tailwheel endorsement; the pilot receiving instruction was practicing three point landings. The first landing was “firm” due to a “higher than normal sink rate.” The next few attempts were low passes so the pilot receiving instruction could practice airspeed control. During the next landing attempt, the airplane “swerved” to the left. The CFI took control of the airplane and corrected toward the runway centerline. While correcting, he heard a loud snapping noise followed by a loud scraping noise and subsequent sudden left turn. The airplane slid, and came to a rest on the left edge of the runway. Post-accident examination of the airplane revealed the fuselage and left wing assembly sustained substantial damaged. Examination of the left main landing gear, by an airframe and powerplant mechanic, revealed that the left landing gear fractured at the inboard end. Photographs of the fracture surface were taken by the NTSB Investigator-in-charge and sent to the National Transportation Safety Board’s Materials laboratory in Washington, D.C. for further examination. An NTSB senior metallurgist reported that the main left landing gear fractured at the inboard end. The inboard fracture face contained a dark crescent-shaped fracture on the lower aft surface which is consistent with features of fatigue cracking. The remaining fracture surface contained a coarse grainy appearance, clear chevron markings, and a shear lip, which are consistent of an overstress fracture. Corrosion damage was also present on the worn surfaces of the left landing gear leg.