Accident Overview
On July 30, 2009, approximately 1530 mountain standard time, a Beech 76, registration N83ER, experienced a left main landing gear collapse while stationary at Glendale Municipal Airport (GEU) in Glendale, Arizona. The flight instructor and private pilot receiving instruction were not injured. The airplane had departed GEU about 1330 for a local instructional flight under visual meteorological conditions, operating under 14 CFR Part 91 without a flight plan.
Landing Gear Failure
According to the flight instructor, after returning from the training flight and preparing to land, the landing gear indicator showed three green lights, confirming all gear were down and locked. Following landing and exiting the runway, the after-landing checklist was completed, and the airplane was taxied to parking. During taxi, the landing gear warning horn activated; the instructor verified the gear handle was down. After the airplane came to a stop, the left main landing gear collapsed, causing substantial damage to the left wing.
Post-Accident Examination
A Federal Aviation Administration inspector examined the landing gear system and found 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 sent to the NTSB Materials Laboratory. An NTSB engineer reported that the down tube had fractured adjacent to its fillet weld. The fracture regions were consistent with stresses from bending moments encountered during gear retraction and extension, as well as takeoff, landing, and taxiing.
Further information from Hawker Beechcraft Corporation indicated that before the enhanced side brace, a weld cluster version was used, which had known fatigue cracking issues near the weld cluster. FAA Airworthiness Directive (AD) 91-14-14 and Hawker Beechcraft Service Bulletin 2361 mandated inspections for fatigue cracks in the older versions. The enhanced part replaced the weld cluster with a machined fitting, and AD 97-06-10 allowed its use without fatigue inspections. The accident airplane's side brace was the enhanced version and was not subject to such inspections. A review of the NTSB Materials Laboratory database showed no other cases of fatigued enhanced side braces with the machined fitting.