ERA11LA484

According to both pilots, they landed the airplane and felt the right wing drop during the landing roll. They attempted to maintain directional control, but the right wing dropped further and the airplane veered off of the right side of the runway. During a subsequent examination of the wreckage, the right main landing gear shock strut drag arm was found broken. An examination of the broken drag arm revealed that it fractured in the I-beam at the blend radius of an orthogonal arm due to bending fatigue. Given the extent of fatigue crack propagation in the flange of the I-beam, it is likely that the fracture occurred due to high-cycle, low-stress fatigue. Since the depth of the fatigue crack was significant relative to the I-beam flange thickness, the fatigue crack probably developed and propagated over a long time under numerous low-stress cycles. The most recent inspection of the main landing gear was on July 7, 2011, which was in accordance with a conditional inspection. The inspection required a mechanic to verify the condition and security of the main landing gear. It is most likely that the fatigue crack would have been detectable at the time of that inspection.

On September 4, 2011, about 1745 eastern daylight time, a North American TB-25N, N9079Z, was substantially damaged during the landing rollout at Sussex County Airport (GED), Georgetown, Delaware. The two pilots and three passengers on board were not injured. The airplane was registered to a corporation and operated under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and there was no flight plan filed. The flight originated from Patuxent River Naval Air Station (NHK), Patuxent River, Maryland, about 1700. According to both pilots, they landed the airplane and during the landing rollout, they felt the right wing drop and heard a noise like "a blown tire." They attempted to maintain directional control of the airplane, but the right wing dropped further and the airplane veered off of the right side of the runway. The airplane came to rest in the grass beside the runway; the pilots secured the airplane, and then exited without incident. During a subsequent examination of the wreckage, a Federal Aviation Administration (FAA) inspector discovered that the airplane sustained substantial damage to the right engine firewall. Also, the right main landing gear shock strut drag arm was found broken. According to the pilot, he held a commercial pilot certificate for airplane multiengine land, a private pilot certificate for airplane single-engine land, and an instrument airplane rating. He also held a type certificate rating for the North American BE25. His most recent second-class medical certificate was issued on January 12, 2011. He reported 4,633 total hours of flight time, of which, 1,344 hours were in the same make and model as the accident airplane. According to FAA records, the copilot held a flight instructor certificate for airplane single-engine land, airplane multiengine land, and instrument airplane. He also held a type rating for the North American BE25. His most recent second-class medical certificate was issued on March 25, 2011. The copilot reported 10,701 total hours of flight time, of which, 1,120 hours were in the same make and model as the accident airplane. According to FAA records, the airplane was manufactured in 1944, and was registered to a corporation in 1999. It was a multiengine, retractable tricycle gear, monoplane that was equipped with two Curtis Wright R-2600 series radial engines. The most recent maintenance inspection in accordance with a manufacturer approved maintenance schedule was performed on July 7, 2011. At that time, the airplane had 2,220.4 hours of total time in service. The airframe maintenance records indicated that both main landing gear were replaced on December 30, 1988. The right main landing gear shock strut drag arm which fractured during the accident sequence accumulated 1,982.1 total hours of time in service. According to the maintenance records, the main landing gear was inspected on July 7, 2011 in accordance with a conditionalinspection. A part of the conditional inspection stated to, "Inspect landing gear upper trusses and brace strut assembly for condition and security." The airplane was signed off as airworthy on that date. An examination of the right main landing gear shock strut drag arm by the Safety Board Materials Laboratory revealed that a fatigue crack initiated on the exterior surface of the I-beam flange adjacent to a blend radius for an orthogonal arm. The fatigue crack initiated at numerous discrete positions on the outer I-beam surface, forming a diffuse initiation zone. A multitude of ratchet marks are present along this initiation zone. No singular defect was identified in the fatigue initiation region.