WPR09LA383

On July 30, 2009, about 1530 mountain standard time, a Beech 76, N83ER, sustained substantial damage following the collapse of the left main landing gear while standing at the Glendale Municipal Airport (GEU), Glendale, Arizona. The flight instructor and private pilot receiving instruction were not injured. Visual meteorological conditions prevailed for the local instructional flight, which was operated in accordance with 14 Code of Federal Regulations (CFR) Part 91, and a flight plan was not filed. The flight departed GEU about 1330. In a statement submitted to the Safety Board investigator-in-charge (IIC), the flight instructor reported that after returning from a local training flight and preparing to land at GEU, he observed 3 green lights, indicating that all 3 landing gear were down and locked. The flight instructor stated that after landing and exiting the runway, the after landing checklist was completed, followed by the airplane being taxied to parking. The flight instructor revealed that while taxiing the landing gear warning horn went off, at which time he checked to ensure that the landing gear handle was down. The instructor reported that after the airplane came to a stop the left main landing gear collapsed. An examination revealed that the left wing had sustained substantial damage. A post accident examination of the airplane's landing gear system by a Federal Aviation Administration (FAA) inspector revealed that the left main landing gear's "enhanced side brace assembly" (main landing gear "A" frame assembly), part number 105-810023-75, had failed. The component was forwarded to the NTSB Materials Laboratory in Washington, D.C., for further examination. As a result of the examination, an NTSB engineer reported that the components down tube had fractured adjacent to its fillet weld. The examination also revealed that the location of the fracture regions in the down tube were consistent with the stresses developed from the bending moments applied to the down tube when raising and lowering the main landing gear, as well as during takeoff, landing, and taxiing. In conversations between Hawker Beechcraft Corporation and the IIC, it was revealed that prior to the introduction of the enhanced version of the side brace assembly, the weld cluster version was used. This version was known to have fatigue cracking issues in the down tube near the weld cluster. Federal Aviation Administration (FAA) Airworthiness Directive (AD) 91-14-14, as well as Hawker Beechcraft Service Bulletin 2361, required inspections around the weld cluster and the down tube to address fatigue cracks in an all welded or weld cluster version of the side brace assembly. Subsequently, the enhanced version of the side brace assembly was developed, which uses a new machined fitting to replace the weld cluster of the older part. FAA Airworthiness Directive AD 97-06-10 allows the enhanced part to be used without inspection for fatigue. The side brace that was installed onthe accident airplane was the enhanced version and did not require a fatigue inspection. A review of the NTSB Materials Laboratory database did not reveal any other cases of fatigued side braces with the enhanced machined fitting.