Accident Overview
On August 11, 2010, at 1150 mountain daylight time, a Cessna A185F, registration N4492, operated by the pilot, was substantially damaged during a ground loop upon landing at Four Corners Regional Airport (FMN) in Farmington, New Mexico. The pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed at the time.
Flight Details
The personal cross-country flight originated at Stinson Municipal Airport (SSF) in San Antonio, Texas, at approximately 0802 central daylight time, with a destination of FMN. The flight was conducted under Title 14 Code of Federal Regulations Part 91 without a flight plan.
Landing and Accident Sequence
According to the pilot, only minimal crosswind correction was required for landing on runway 25. After rolling a few hundred feet, the airplane "swerved very strongly to the right." Applying opposite brake and rudder had no effect. The airplane departed the runway and impacted terrain. The left landing gear collapsed, and the left elevator sustained leading edge damage. The outboard portion of the left wing was bent upward at a 20-degree angle across its entire width, starting from the middle of the left aileron.
Post-Accident Examination
FAA inspectors examined the airplane and found that the through-bolt attaching the inboard end of the left gear leg to the airframe hard-point had pre-existing damage. After recovery and transport to Beegles Aircraft Services in Greeley, Colorado, examination of the through-bolt revealed threads from a failed nut embedded in the bolt's threads. Beegles personnel concluded that the nut had failed and stripped off the bolt, leaving the inboard end of the gear leg loose and free to move vertically, which allowed fore-and-aft movement. Chaffing on the longeron inboard of the gear leg attach point indicated that the bolt-nut combination had been loose for an extended period. The bolt was measured, and it was questioned whether it was an AN7-22A rather than the specified AN7-20A, making it 1/4 inch (8/32) too long. If the nut ran to the end of the bolt's threads, insufficient tension would result between the bolt head and attaching block. The FAA could not determine if the bolt was a stretched -20A or a -22A. Beegles also observed indications of looseness on the right gear leg attach bolt after removal.
Examination of the wheels, brakes, and brake pads revealed no anomalies. A review of the logbooks and the work order for the last annual inspection did not indicate whether the left gear leg attaching bolt was checked for correct torque or length. The right side bolt and nut were replaced during that inspection.
Weather Conditions
At the time of the accident, the Automatic Terminal Information Service (ATIS) was reporting the wind as variable from 150 degrees at 3 knots.