ANC06TA009

A commercial certificated pilot in a tundra tire-equipped airplane from a CFR Part 135 operator, 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 of the left gear strut dug into the ground, the airplane swerved 90 degrees to the left and nosed down, receiving structural damage to the left wingtip and the right main landing gear. The main landing gear is a spring steel strut that is shot peened during manufacture, and is bolted to the fuselage at its upper end. Photographs of the point of separation 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 end of the strut, containing the axle and brake assembly, had a rough, crystalline appearance with darkening of the metal surface along the outer edges of the strut. The fractured surface of the upper end of the strut, 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 or 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. 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 reported to the NTSB that the current inspection criteria outlined in the Cessna Maintenance Manual are adequate to detect cracks in the main landing gear struts, and that additional airworthiness action is not warranted. On March 25, 2002, the NTSB responded by stating, in part: "The Safety Board continues to believe that a visual inspection alone will not detect cracks in the Cessna main landing gear spring struts. However, the Safety Board acknowledges that the statistical evidence does not warrant issuance of ADs at this time as called for in the Board's recommendation." 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 area of the report: Recommendation (How Could This Accident Have Been Prevented), the pilot wrote: "Put time life [limit] on gear legs."

On November 5, 2005, about 1030 Alaska Standard time, a tundra tire-equipped Cessna 185 airplane, N771X, sustained substantial damage when the left wheel and axle separated from the left main landing gear strut during the landing roll at a remote airstrip on Hinchingbrook Island, about 20 miles southwest of Cordova, Alaska. Fish and Flying, a CFR Part 135 operator from Cordova, provided the pilot and airplane under contract to the Federal Aviation Administration (FAA). The airplane was being operated by the FAA Airways Facilities Technical Operations, South Alaska System Management Office (SA SMO), Anchorage, Alaska, as a visual flight rules (VFR) cross-country public use flight when the accident occurred. The pilot was transporting two FAA Turnagain System Support Center (TGN SSC) personnel from their Cordova office to perform maintenance at a navigational facility on the island. The commercial certificated pilot and one passenger were not injured; one passenger received minor injuries. Visual meteorological conditions prevailed, and VFR company flight following procedures were in effect. The flight originated at the Merle K. (Mudhole) Smith Airport, Cordova, about 1010.

During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on November 7, the pilot reported that she was landing toward the east on a dirt surface runway on the island. 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 onto the strut. The left wheel and axle were initially attached to the airplane by the hydraulic brake hose, but then separated. The fractured end of the left gear strut dug into the ground, and the airplane swerved 90 degrees to the left and nosed down. The pilot said that the airplane received structural damage to the left wingtip, the right main landing gear, and the propeller.

After the airplane was recovered, a Federal Aviation Administration (FAA) air safety inspector, Flight Standards District Office, Anchorage, Alaska, examined the airplane and provided photographs of the broken strut. The photographs revealed the point of separation was 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 end of the strut, containing the axle and brake assembly, had a rough, crystalline appearance with darkening of the metal surface along the outer edges of the strut. The fractured surface of the upper end of the strut, where it dug into the ground, had a smooth polished appearance.

The landing gear on the accident airplane is a spring steel strut that is shot peened during manufacture, and is bolted to the fuselage at its upper end. It is braced by a fuselage support bracket at the outer edge of the fuselage. Visual inspection of the landing gear strut is required at prescribed intervals by 14 CFR Part 43. Removal of the gear for visual inspection, or the use of nondestructive inspection techniques (NDT), is not required. Neither the manufacturer nor the FAA, have established a life limit (hours or cycles) for the main landing gear strut.

The Safety Board issued Safety Recommendations A-01-01 and A-01-02 on March 16, 2001, that recommended the FAA issue airworthiness directives (AD) for initial and repetitive inspection of tailwheel-equipped Cessna 170, 180, 185, 190, and 195 series airplanes main landing gear spring struts. The Safety Board noted that Cessna tailwheel-equipped airplanes and Cessna nose wheel-equipped airplanes have main landing gear spring struts of similar design, but also indicated that there were only 5 reports of nose wheel-equipped main landing gear fatigue failures.

On August 31, 2001, the FAA indicated that there was not enough evidence to support an AD. The FAA indicated that the Cessna Maintenance Manual specified inspections of the landing gear every 50 hours and during annual inspections, and that these inspections were adequate to detect cracks in the main landing gear struts and additional action was not warranted. The FAA also indicated that a General Aviation Alert in Advisory Circular 43-16A (August 2001) was published to reiterate that visual inspections of the spring strut should be performed every 50 hours and during annual inspections as required by the Cessna maintenance manuals.

On March 25, 2002, the NTSB responded to the FAA by stating, in part: "The Safety Board continues to believe that a visual inspection alone will not detect cracks in the Cessna main landing gear spring struts. However, the Safety Board acknowledges that the statistical evidence does not warrant issuance of ADs at this time as called for in the Board's recommendation." The Safety Board subsequently classified Safety Recommendations A-01-01 and A-01-02 as "Closed, Reconsidered."

In the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) submitted by the pilot, the pilot indicated that the landing gear strut, Part number 0741001-5, had accrued about 9,000 hours of service. In the optional area of the report; Recommendation (How Could This Accident Have Been Prevented), the pilot wrote: "Put time life [limit] on gear legs."