Accident Overview
On February 7, 2021, at approximately 1400 Pacific standard time, a Piper PA-44-180 airplane, registration N125MG, was substantially damaged during an instructional flight at Roberts Field Airport (RDM) in Redmond, Oregon. The aircraft was operated under Title 14 Code of Federal Regulations Part 141. The flight instructor and two pilots receiving instruction were not injured.
Sequence of Events
According to the flight instructor, the flight was an instructional sortie with one of the two pilots receiving instruction flying the aircraft while the other observed. Several takeoffs and landings had been completed prior to the accident landing. On the accident landing, the pilot receiving instruction flew a stabilized approach, touched down, and decelerated smoothly. During the rollout, the instructor took control, felt a pull to the right, and suspected a flat tire. He attempted to maintain directional control, but the right wing continued to sink. The right main landing gear then separated from the wing and struck the rear of the wing, resulting in substantial damage.
Post-Accident Examination
A postflight inspection by the operator’s maintenance personnel found that the strut piston tube, a component of the right main landing gear strut assembly, had fractured, allowing the gear to separate. Examination at the National Transportation Safety Board’s Materials Laboratory revealed two thumbnail-shaped fatigue cracks on the strut piston tube. These cracks originated from corrosion pits near a drilled hole. One crack measured 0.21 inch in length; the other measured 0.33 inch. Both cracks extended through the piston wall thickness of 0.125 inch.
Maintenance and Service Information
The airplane’s most recent annual inspection was completed on November 7, 2020, at which time the aircraft had accumulated 11,614.5 hours. At the accident, total time was 11,769.5 hours, which was also the time in service of the failed strut piston tube.
On December 23, 2020, Piper Aircraft Incorporated issued Service Letter 1263, applicable to the PA-44-180, titled “Main Landing Gear Piston Tube Inspection.” The service letter called for an initial inspection of main landing gear strut assemblies with 6,500 hours or more time in service, or with unknown service history, at the next regularly scheduled maintenance event but not to exceed the next 100 hours. The purpose section noted that fatigue cracks can develop at the bolt hole in the piston tube common to the fork. Diagrams indicated that the cracks found on the accident aircraft were in the area specified for inspection.
According to the director of maintenance, as a Part 141 certificate holder, the operator was not obligated to comply with service letters. The operator stated they strived to be aware of service information and complied with most service directives, but had not yet incorporated Service Letter 1263 into their maintenance program before the accident. Following the accident, the operator incorporated the repetitive inspection called for in the service letter.