Fairbanks, AK, USA
N1837M
CURTISS WRIGHT C-46F
During the maintenance test flight, the flight crew moved the landing gear handle to the "down" position but did not observe the three green landing gear down-and-locked lights illuminate. After cycling the landing gear "several" times they observed a gear down-and-locked indication in the cockpit. After landing, while taxiing to parking, the right main landing gear collapsed, and the right wing and aileron struck the ground and sustained substantial damage. The right landing gear side brace fractured near the fuselage attach forging due to fatigue, which initiated near the weld between the large end fuselage attach forging and the outer tube. No obvious discontinuities such as porosity or undercutting were visually noted in the weld adjacent to the fracture.
On July 2, 2013, about 1600 Alaska daylight time, a twin-engine Curtiss Wright, C-46F airplane, N1837M, sustained substantial damage while taxiing to parking at the Fairbanks International Airport, Fairbanks, Alaska. The commercial certificated captain and the airline transport certificated first officer were not injured. The airplane was registered to and operated by Evert's Air Fuel, under the provisions of Title 14 Code of Federal regulations Part 91, as a visual flight rules (VFR) maintenance test flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The operator reported that during the maintenance test flight, the flight crew moved the landing gear handle to the "down" position, but did not observe the three green landing gear down-and-lock lights illuminate. After cycling the landing gear "several" times they observed a gear down-and-locked indication in the cockpit. After landing, while taxiing to parking, the right main landing gear collapsed, and the right wing and aileron sustained substantial damage. A postaccident examination, of the landing gear system revealed that both inner and outer tubes of the right landing gear side brace, separated near the fuselage attach forging. The fractured main landing gear side brace assembly was sent to the NTSB's Materials Laboratory in Washington, D.C. for examination. A senior Safety Board metallurgist reported that a magnified optical examination of the landing gear side brace assembly fracture surfaces revealed ratchet marks, arrest lines, and flat fracture regions consistent with fatigue propagation. No obvious discontinuities such as porosity or undercutting were visually noted in the weld adjacent to the fracture. A complete copy of the NTSB's materials laboratory factual report is included in the public docket for this accident. In the recommendation section of the NTSB Accident/Incident Reporting Form 6120.1, the operator stated that the accident may have been prevented if the flight crew would have shut down the airplane clear of the runway, and had the landing gear inspected before taxiing to parking. They also noted, that three green down-and-lock lights illuminated is the normal indication for a positive lock.
The failure of the right main landing gear side brace due to fatigue, which resulted in a collapse of the right main landing gear.
Source: NTSB Aviation Accident Database
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