On January 14, 2018, about 1445 Alaska standard time, a Cessna 210 airplane, N3607Y, was substantially damaged when it was involved in an accident in Juneau, Alaska. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that, while approaching JNU for landing, he extended the landing gear; the nose gear extended fully, but the left and right main gear only partially extended and the landing gear position indicator light did not illuminate. He attempted to manually extend the gear by use of the emergency hand pump; however, after a few pumps, he felt a loss of pressure feedback in the handle and the landing gear failed to fully extend. He then extended the wing flaps, but no flap movement was evident. During the landing roll, the left and right main landing gear collapsed and the right wing tip and right horizontal stabilizer impacted the runway, resulting in substantial damage. The pilot noted hydraulic fluid leaking from under the airplane as it was subsequently removed from the runway. Examination of the hydraulic system revealed that the right main landing gear hydraulic actuator (P/N 1280501-2, Electrol EA1614-2) was fractured about the barrel section adjacent to the end cap. (see Figure 1.)

Figure 1. Right main landing gear actuator exhibiting fractures. A detailed examination was conducted at the National Transportation Safety Board Materials Laboratory. The actuator was partially disassembled, and a singular, thumbnail-shaped crack was present at the retainer clip groove. The fracture surface exhibited striations consistent with fatigue crack propagation when examined using a scanning electron microscope. Fractured surfaces outside of the fatigue crack area exhibited dimple rupture, consistent with an overstress fracture. The retaining ring groove revealed multiple small corrosion pits. The airplane manufacturer issued a service letter (SE75-21) in 1975 that recommended that Electrol actuators in certain Cessna 210 airplanes be modified with an actuator repair kit during the next annual or 100-hour inspection. The instructions required disassembly, inspection, and replacement of certain internal parts. In 1976, the Federal Aviation Administration issued an airworthiness directive (AD 76-04-01) that mandated the service letter instructions for the actuator. In 2011, the manufacturer also issued a service manual Supplemental Inspection Number 32-10-01 that required visual inspection of the main landing gear actuators for cracks, wear, and corrosion at regular intervals. Due to limited maintenance records available, it could not be determined if the accident airplane had been maintained in accordance with the AD or supplemental inspections.