Redmond, OR, USA
N125MG
PIPER PA-44-180
During the instructional flight, the right main landing gear separated during landing roll following a normal touchdown. The separated right landing gear assembly then struck the rear edge of the wing, which resulted in substantial damage to the wing. Examination revealed that the right landing gear strut piston tube had failed due to two fatigue cracks that had originated from corrosion pits near a drilled hole. Two months before the accident, the manufacturer had issued a service letter applicable to the airplane that called for inspection of the strut piston tube for fatigue cracks. Performance of the inspection called for in the service letter would have discovered the cracks that led to the accident. Although the operator held a Part 141 certificate, they were not required to comply with the service letter.
On February 7, 2021, about 1400 Pacific standard time, a Piper PA-44-180 airplane, N125MG, was substantially damaged when it was involved in an accident at Roberts Field Airport (RDM), Redmond, Oregon. The flight instructor and two pilots receiving instruction were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 141 instructional flight. According to the flight instructor, this was an instructional flight with one of the two pilots receiving instruction flying and the other observing. They had performed multiple takeoffs and landings before the accident. On the accident landing, the pilot receiving instruction flew a stabilized approach to a touchdown followed by a smooth deceleration. While on the rollout, the flight instructor took the controls, felt a pull to the right, and thought it might be a flat tire. He worked to maintain directional control; however, the right wing continued to sink. The right main landing gear separated from the wing and struck the rear of the wing, which resulted in substantial damage to the wing. A postflight inspection by the operator’s maintenance personnel revealed the strut piston tube, a component of the right main landing gear strut assembly, had fractured, which allowed the right main landing gear to separate from the wing. Examination of the components of the landing gear strut assembly at the National Transportation Safety Board’s (NTSB’s) Materials Laboratory revealed two thumbnail-shaped fatigue cracks on the strut piston tube that had originated from corrosion pits near a drilled hole. One crack was 0.21 inch in length, and the other was 0.33 inch in length. Both encompassed maximum widths equivalent to the piston wall thickness of 0.125 inch. The airplane’s most recent annual inspection was completed on November 7, 2020, and it had accumulated 11,614.5 hours at that time. The operator reported that at the time of the accident, the airplane had accumulated 11,769.5 hours and that this was also the time in service of the failed strut piston tube. On December 23, 2020, Piper Aircraft Incorporated published Service Letter 1263, applicable to the PA-44-180 and titled “Main Landing Gear Piston Tube Inspection.” The compliance time section of the service letter stated in part: Initial inspection: For airplanes with main landing gear strut assemblies that have 6,500 hours or more time in service (TIS), and airplanes with an unknown service history of the main landing gear strut assemblies, initial inspection is to occur at the next regularly scheduled maintenance event, but not to exceed the next 100 hours TIS. The purpose section of the service letter stated in part: A review of service history reveals that fatigue cracks can develop in the main landing gear of the affected airplanes; specifically, at the bolt hole in the piston tube common to the fork. Review of the diagrams in the service letter revealed that the fatigue cracks found on the airplane’s piston tube were in the specific area called out for inspection by the service letter. According to the director of maintenance, as the holder of a Part 141 certificate, the operator was not obligated to comply with service letters. He indicated that they did strive to be aware of all service information and did comply with most service directives. Regarding Service Letter 1263, he stated that the information from the manufacturer was new, and they had not incorporated it into their maintenance program before the accident. Following the accident, they did incorporate the repetitive inspection called for in the service letter.
Failure of the landing gear strut piston tube due to fatigue cracking from corrosion pitting.
Source: NTSB Aviation Accident Database
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