Accident Details
On June 22, 2018, at approximately 1730 Alaska daylight time, a tailwheel-equipped Cessna 180, registration N3125D, sustained substantial damage during an off-airport landing at Upper St George Creek, about 50 miles south of Fairbanks, Alaska. The aircraft was operated by the pilot as a personal flight under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The flight had departed Fairbanks International Airport around 1700.
Pilot's Account
According to the pilot, the landing was being performed with a right crosswind. After touchdown, as the airplane decelerated, the pilot applied left brake to maintain directional control. He reported that the left rudder/brake pedal felt "soft" and traveled to its full forward limit, at which point directional control was lost. The airplane weathervaned into the wind and skidded sideways before the left main wheel departed the cleared landing area and entered brush. The left wing and left horizontal stabilizer subsequently impacted terrain, resulting in substantial damage.
Examination Findings
Upon exiting the airplane, the pilot discovered that the brake line had separated at the compression fitting near the brake caliper, at the transition from rigid to flexible line. The brake line tube and fitting hardware were removed and sent to the NTSB Materials Laboratory for evaluation. The interior surface of the failed end exhibited circumferential marks up to 0.136 inch from the end, consistent with formation of a flared end using a flaring tool. The sleeve was trapped within the nut from the failed end, and deposits of gray metal, consistent with deformed brake tube material, were observed on the internal threads of the nut up to three threads from the end of the sleeve.
Federal Aviation Administration Advisory Circular AC 43-13-1B specifies that a double flare is used on soft aluminum tubing with an outside diameter of 3/8 inch or less. No evidence of folded walls consistent with a double flare was found at either end of the submitted brake line tube. No records could be located that indicated the manufacture or assembly date of the fractured brake line components.