Cessna 180 N3125D accident near Fairbanks, Alaska

Probable cause

The failure of the brake line tube due to an improper flare.

NTSB analysis

According to the pilot, he was landing with a right crosswind, and after touchdown, as the airplane began to decelerate, he applied left brake to maintain directional control. He stated that the left brake pedal was "soft" and traveled to its full forward limit. The airplane weathervaned and skidded sideways before the left main wheel went off the landing area and into brush. The left wing and left horizontal stabilizer impacted terrain, which resulted in substantial damage. The pilot noted in a postflight examination that the brake line had separated at the compression fitting near the brake caliper where the brake line transitioned from a rigid line to a flexible line.

A laboratory examination of the brake line and its components revealed that the interior surface of the failed end had circumferential marks consistent with formation of a flared end with a flaring tool. The sleeve was trapped within the nut from the failed end, and deposits of gray metal appearing consistent with deformed brake tube material were observed deposited on internal threads of the nut.

According to Federal Aviation Administration Advisory Circular AC 43-13-1B, "Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair," a double flare is used on soft aluminum tubing having a 3/8-inch outside diameter or less. No evidence of folded walls consistent with a double flare was noted at either end of the brake line tube.

No records could be found that showed the manufacture or assembly date of the fractured brake line components.

Text from the NTSB. Open the NTSB docket for ANC18LA048 for the full record.