What happened
On July 2, 2013, at approximately 1600 Alaska daylight time, a Curtiss Wright C-46F, registration N1837M, was conducting a visual flight rules (VFR) maintenance test flight at Fairbanks International Airport in Fairbanks, Alaska. During the flight, the crew moved the landing gear handle to the down position but initially failed to see the three green down-and-lock lights illuminate. After cycling the gear several times, the cockpit indicators showed the gear was down and locked.
Following the landing, the aircraft was taxiing to its parking position when the right main landing gear collapsed. This caused the right wing and aileron to strike the ground, resulting in substantial damage to the aircraft. The captain and first officer were not injured.
The investigation
An examination of the landing gear system determined that both the inner and outer tubes of the right landing gear side brace had separated near the attachment forging on the fuselage.
Metallurgical analysis of the fractured side brace assembly by the NTSB Materials Laboratory revealed ratchet marks, arrest lines, and flat fracture regions. These findings are consistent with fatigue propagation. The fatigue initiated near the weld between the outer tube and the large end fuselage attach forging, though no obvious porosity or undercutting was found in the adjacent weld.