Cessna 140 N89965 accident near Salinas, California

Probable cause

The fatigue failure of a bulkhead-skin joint that supported the main landing gear leg, which resulted in the collapse of the left main landing gear. Contributing to the failure were the non-original structural configuration of the 60-year-old airplane and the relative inaccessibility for inspection or cleaning of the structure in the region of the fatigue failure.

NTSB analysis

The private pilot made a normal landing in his 1946 tailwheel-equipped airplane. During the landing roll, the left wing began to dip. The pilot applied opposite aileron, but the airplane continued to roll to the left, and the cabin floor deformed upward. The left wing and propeller struck the runway surface, and the airplane came to a stop on the runway shortly thereafter. Postaccident examination revealed that the left main landing gear leg had rotated aft and up, and that the landing gear leg support structure formed by two transverse bulkheads and portions of the lower fuselage skin had failed. Comparisons of fasteners, skin, and fairing panels revealed some discrepancies between the existing configuration and the original design, but the exact pre-accident configuration and condition could not be determined. Detailed laboratory examination revealed that the joint between the aft landing gear bulkhead and the lower fuselage skin had failed in fatigue. The fatigue failure sites were in a region of the airplane's structure that was not readily accessible for cleaning or inspection, and some sludge-like deposits of unidentified substance were observed in the location of the fatigue failure.

Text from the NTSB. Open the NTSB docket for WPR16LA139 for the full record.