What happened
A commercial pilot was transporting Federal Aviation Administration (FAA) personnel to a navigational facility located on a remote island. The aircraft, a Cessna equipped with tundra tires, was performing a landing on a dirt surface runway. During the landing roll, the lower end of the left main landing gear strut fractured at the axle bolt holes where the axle is bolted to the strut. This failure caused the fractured end of the gear strut to dig into the ground, resulting in the aircraft swerving 90 degrees to the left and nosed down. The impact resulted in structural damage to the right main landing gear and the left wingtip. There were no injuries reported.
The investigation
The investigation focused on the fracture of the spring steel landing gear strut, which is bolted to the fuselage at its upper end. Examination of the separation point revealed a vertical fracture oriented 9 and degrees to the span of the gear strut through the upper axle retaining bolt holes. The fractured surface of the lower end of the strut, which contained the axle and brake assembly, exhibited a rough, crystalline appearance with darkening of the metal surface along the outer edges. In contrast, the fractured surface of the upper end of the strut, where it had dug into the ground, presented a smooth, polished appearance. The pilot reported that the landing gear strut (Part number 0741001-5) had accumulated approximately 9,000 hours of service.
Findings
- The aircraft was operating as a public use flight under contract to the FAA.
- Neither the manufacturer nor the FAA had established specific service life limits, such as hours or cycles, for the main landing gear strut.
- Periodic visual inspections are required by 14 CFR Part 43, but neither the manufacturer nor the FAA requires the removal of the gear strut for inspection or the use of nondestructive inspection techniques.
- While the NTSB recommended an airworthiness directive for nondestructive inspections of these struts, the FAA determined that existing maintenance manual criteria were adequate.