Accident Description
A commercial certificated pilot operating a tundra tire-equipped airplane under contract to the Federal Aviation Administration (FAA) as a public use flight was transporting FAA personnel to a navigational facility on a remote island. During the landing roll on a dirt surface runway, the lower end of the left main landing gear strut fractured at the axle bolt holes, where the axle is bolted onto the strut. The fractured end dug into the ground, causing the airplane to swerve 90 degrees to the left and nose down. Structural damage occurred to the left wingtip and the right main landing gear.
Landing Gear and Inspection
The main landing gear is a spring steel strut that is shot peened during manufacture and bolted to the fuselage at its upper end. Photographs of the separation point revealed a vertical fracture oriented 90 degrees to the span of the gear strut, through the upper axle retaining bolt holes. The fractured surface of the lower strut end, containing the axle and brake assembly, had a rough, crystalline appearance with darkening of the metal along the outer edges. The fractured surface of the upper strut end, where it dug into the ground, had a smooth polished appearance.
Periodic visual inspection of the landing gear is required by 14 CFR Part 43. Neither the manufacturer nor the FAA have established service limits (hours or cycles) for the main landing gear strut. Removal of the gear strut for inspection or the use of nondestructive inspection techniques is not required by the manufacturer or the FAA.
Post-Accident Recommendations
In the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1), the pilot indicated that the landing gear strut, Part number 0741001-5, had accrued about 9,000 hours of service. In the optional recommendation area, the pilot wrote: "Put time life [limit] on gear legs."
On March 16, 2001, the NTSB recommended that the FAA issue an airworthiness directive (AD) to require an initial and recurring inspection of Cessna main landing gear spring steel struts using nondestructive inspection techniques. On August 31, 2001, the FAA responded that the current inspection criteria in the Cessna Maintenance Manual are adequate to detect cracks, and that additional airworthiness action was not warranted. On March 25, 2002, the NTSB acknowledged that while visual inspection alone would not detect cracks, statistical evidence did not warrant issuance of ADs at that time.