DELTA JUNCTION, AK, USA
N85LC
Cessna 185F
The airline transport certificated pilot was landing a tailwheel equipped airplane on an airstrip near a remote cabin on an on-demand air taxi flight. The airstrip had been used by the pilot in the past. Near the end of the landing roll, the left main landing gear strut fractured above the left wheel axle. The wheel and the lower end of the gear strut separated from the airplane. The upper portion of the gear strut dug into the ground, and the airplane nosed over. The airplane received damage to the right wing, propeller, the vertical stabilizer, and the rudder. The lower end of the gear strut has four holes drilled through the metal to facilitate the installation of the wheel axle and brake assembly. An examination of the landing gear strut found areas of cracking, typical of fatigue, emanating from the inboard edge of the forward, upper bolt hole. One crack developed in an area of two small corrosion pits in the drilled hole. A second crack developed in an area of the fillet between the drilled hole, and the inboard surface of the strut. The cracks from the two areas combined to form one crack laterally across the strut and through the aft, upper bolt hole. The interior surfaces of the forward, upper bolt hole and fillet regions were pitted, consistent with the effects of corrosion. Neither the manufacturer nor the FAA, have established a life limit (hours or cycles) for the main landing gear strut. An annual inspection does not require disassembly of the axle from the gear strut. No inspection procedures, other than a general visual inspection of the landing gear, have been specified by the manufacturer, or the FAA.
On September 14, 1999, about 1630 Alaska daylight time, a wheel equipped Cessna 185 airplane, N85LC, sustained substantial damage during landing at a remote airstrip about 38 miles southwest of Delta Junction, Alaska, at latitude 63 degrees, 52.78 minutes north, and longitude 147 degrees, 08.8 minutes west. The airplane was being operated as a visual flight rules (VFR) on-demand passenger flight under Title 14 CFR Part 135 when the accident occurred. The airplane was operated by Tamarack Air LTD., Fairbanks, Alaska. The airline transport certificated pilot, and one passenger received minor injuries; the remaining passenger was not injured. Visual meteorological conditions prevailed. Company VFR flight following procedures were in effect. The flight originated at the Fairbanks International Airport, Fairbanks, Alaska, about 1550. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on September 14, 1999, the pilot said he was landing at an airstrip near a cabin. The airstrip is oriented in a northeast/southwest direction, and has been used by the pilot in the past. It is about 1,200 feet long, and about 12 feet wide. The pilot said he landed toward the northeast with a headwind of about 10 knots. Near the end of the landing roll, the left main landing gear strut fractured above the left wheel axle. The wheel and the lower end of the landing gear strut separated from the airplane. The upper portion of the gear strut dug into the ground, and the airplane nosed over. The airplane received damage to the right wing, propeller, the vertical stabilizer, and the rudder. The lower end of the landing gear strut has four holes drilled through the metal in a box pattern. The axle assembly, utilized when wheels and tires are installed, is attached to the outboard side of the strut. When wheel ski landing gear is utilized, the wheel ski assembly is bolted to the landing gear strut through the four holes. Examination of the broken left main landing gear strut revealed a fracture through the upper two holes in the gear strut. The fractured pieces of the gear strut were examined at the NTSB Materials Laboratory. The examination found areas of cracking, typical of fatigue, emanating from the inboard edge of the forward, upper bolt hole. One crack developed in an area of two small corrosion pits in the drilled hole. A second crack developed in an area of the fillet between the drilled hole, and the inboard surface of the strut. The cracks from the two areas combined to form one crack laterally across the strut and through the aft, upper bolt hole. The interior surfaces of the forward, upper bolt hole, and fillet regions were pitted, consistent with the effects of corrosion. Neither the manufacturer (Cessna Aircraft), nor the Federal Aviation Administration (FAA), have established a life limit (hours or cycles) for the main landing gear strut. An annual inspection does not require disassembly of the axle from the gear strut. No inspection procedures, other than a general visual inspection of the landing gear, have been specified by the manufacturer, or the FAA.
Corrosion and a fatigue failure of the lower end of the landing gear strut. Factors in the accident were the manufacturer's and the FAA's insufficient standards/requirements for life limits and inspection procedures.
Source: NTSB Aviation Accident Database
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