Accident Summary
On July 2, 2013, at approximately 1600 Alaska daylight time, a twin-engine Curtiss Wright C-46F, registration N1837M, sustained substantial damage while taxiing to parking at Fairbanks International Airport, Fairbanks, Alaska. The commercial certificated captain and airline transport certificated first officer were not injured. The airplane was registered to and operated by Evert's Air Fuel under 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.
Events Leading to the Incident
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. Following landing, while taxiing to parking, the right main landing gear collapsed, resulting in substantial damage to the right wing and aileron.
Postaccident Examination
A postaccident examination of the landing gear system revealed that both inner and outer tubes of the right landing gear side brace had 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 further examination.
Metallurgical Findings
A senior Safety Board metallurgist reported that a magnified optical examination of the fracture surfaces showed 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.
Operator Recommendations
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 had 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.