Accident Sequence
On June 12, 2019, at approximately 1725 central daylight time, a Beech E90 airplane, registration N176TW, experienced a right main landing gear (MLG) failure during takeoff from Majors Airport (GVT) in Greenville, Texas. The flight was a Title 14 Code of Federal Regulations Part 91 instructional flight operated by Ameristar Jet Charter, Inc., and registered to Sierra American Corporation. Two airline transport pilots and a company check pilot were on board; none were injured. Day visual meteorological conditions prevailed, and a visual flight rules flight plan was filed.
According to the operator, the pilots were conducting an instructional flight involving multiple takeoffs and landings at GVT. During the accident takeoff, the pilots heard a loud noise. With assistance from ground witnesses, they determined that the right MLG wheel assembly had departed the airplane. The separated wheel assembly and fractured components were located near the runway at GVT. The pilots elected to perform an emergency landing at Fort Worth Alliance Airport (AFW) due to its large runways and available emergency personnel and equipment. The airplane landed and came to rest upright on the runway surface.
Examination Findings
Examination of the airplane revealed that the right main wheel and tire, along with the lower shock absorber assembly, had separated from the upper shock absorber assembly. The separated assembly then impacted the right horizontal stabilizer, causing substantial damage. The lower shock absorber assembly was recovered at GVT and retained for further materials examination.
On June 27, 2019, at Textron Aviation in Wichita, Kansas, the right MLG assembly was examined by Textron Aviation engineers under the supervision of a Federal Aviation Administration (FAA) engineer. According to the Textron engineering report, the MLG fractured at the connection between the upper and lower torque knees (part numbers 50-810032-4 and 50-810295-17) and at two other connection points in the upper torque knee. The examination yielded the following findings:
1. The upper torque knee fractured at all three connection points. 2. Fatigue was identified on a fractured piece of the upper torque knee; all other fractures were consistent with overload. 3. Corrosion assisted in crack initiation, and the crack propagated through fatigue until a critical crack length was reached. 4. Material chemistry, tensile properties, conductivity, and microstructure of the upper torque link were consistent with aluminum alloy 2014 in the T6 condition.
The Textron engineering report was reviewed and approved by the National Transportation Safety Board materials laboratory chief engineer.
Maintenance History
According to Textron, due to historical evidence of such occurrences, mandatory service bulletin SB 32-3134 was released in July 1999, requiring non-destructive inspection of the torque knees at reduced intervals. The mandatory inspection was to be accomplished within the next 100 cycles (1 cycle = 1 landing) or at the next scheduled inspection for MLG torque knees with accumulated time in service of 1,000 hours. Recurring inspections were required every 1,000 cycles or 2 years, whichever occurred first. An additional service bulletin, SB 32-3116, was released in October 1999, recommending replacement of the upper and lower torque knees with steel components and removing the 1,000-cycle/2-year inspection requirement from SB 32-3134. On February 22, 2002, the FAA issued airworthiness directive 2002-01-10, which mandated repetitive inspection and/or replacement of the torque knees per the service bulletins.
A review of the aircraft records showed that the upper torque knee underwent fluorescent penetrant inspection on March 25, 2016 (airframe total time: 11,230.4 hours; landings: 10,505) and on February 10, 2017 (time and landings unknown). At the time of the accident, the airframe total time was 11,423.5 hours with 10,715 landings.