CEN10LA315

When the crew retracted the landing gear after takeoff, they heard a loud "bang." When they lowered the gear, all three landing gear annunciator lights indicated SAFE, but the left gear light also indicated IN TRANSIT. After consulting with their maintenance department, the crew landed and, during rollout, the left main gear collapsed. Postaccident examination revealed the drag leg assembly was fractured. When the gear collapsed, a portion of the wing spar was torn out. Metallurgical examination revealed that both lugs that attach to the landing gear actuator and the rig plate were fractured and the drag leg was bent. The right-hand lug contained a fatigue crack that progressed to an overload failure. The other lug fractured completely through overload. The damage was pre-existent to that cracking, and served as a stress concentrator leading to the initiation of a fatigue crack. Spectrographic analysis of the upper drag leg arm showed that it met specified chemical composition requirements. At time of accident the aircraft had operated about 82.9 hours and 95 cycles since a detailed inspection of the landing gear was accomplished on May 28, 2010; no discrepancies related to the lug were noted at that time.

On June 12, 2010, approximately 1625 mountain daylight time, a Beech 1900D, N195GL, registered to and operated by Great Lakes Aviation, Ltd., Cheyenne, Wyoming, was substantially damaged when the left main landing gear collapsed on landing at Denver International Airport (DEN), Denver, Colorado. Visual meteorological conditions (VMC) prevailed at the time of the accident. The positioning flight was being conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91, and an instrument flight rules (IFR) flight plan had been filed. The airline transport certificated captain and commercial certificated first officer, the only occupants aboard, were not injured. The cross-country flight had just originated, and was destined for Cheyenne, Wyoming. When the crew retracted the landing gear after takeoff, they heard a loud "bang." The crew circled the airport. When they lowered the landing gear, all three landing gear annunciator lights indicated SAFE, but the IN TRANSIT annunciator light also illuminated. After consulting with their maintenance department, the crew landed on runway 35R. During rollout, the left main gear collapsed. Post-accident examination revealed the drag leg assembly was fractured. When the gear collapsed, a portion of the wing spar bent. On July 22, 2010, acting on behalf of the National Transportation Safety Board, representatives of the Federal Aviation Administration examined the drag leg assembly at Hawker Beechcraft’s Metallurgical Engineering Laboratory in Wichita, Kansas. Also in attendance were representatives from Great Lakes Aviation. The examination revealed that both lugs that attach to the landing gear actuator were fractured, as was the rig plate. The drag leg was bent. The right hand lug contained a fatigue crack that progressed to an overload failure. The other lug fractured completely through overload. Beach marks associated with the fatigue crack were clearly visible. The fracture surface was damaged by mating crack face abrasion. Striations and mechanical damage was also noted. The damage was pre-existent to the cracking, and served as a stress concentrator leading to the initiation of a fatigue crack. The upper drag leg arm is made of aluminum alloy 7075 in the T6 temper. Spectrographic analysis showed that the material met the chemical composition requirements of that specification. Aerospace Material Specification (AMS) 2658 requires this material in the T6 temper to have a minimum Rockwell hardness of B scale 84 and a conductivity between 30.5 % IACS (International Annealed Copper Standard) and 36 % IACS. The drag leg had a Rockwell hardness of B87.7 and displayed an electrical conductivity of 32% IACS.