Piper PA-31-350 N555GK accident near Franklin, North Carolina

Probable cause

The failure of the left main landing gear brake line during landing due to the loss of hydraulic fluid. Contributing to the accident was a fatigue crack through the brake line that had formed due to contact with a swaged sleeve as a result of exfoliation corrosion.

NTSB analysis

The pilot reported that, during the preflight inspection, he checked both the left and right brake reservoirs for proper servicing, and he found that they were ready for flight. During the landing roll, the pilot applied the left and right brake pedals; however, the left brake did not respond, and the airplane departed the right side of the runway.

Postaccident examination of the airplane revealed that there was a hydraulic fluid leak in the left main landing gear brake line. Further examination revealed that the brake line failed due to a fatigue crack that had propagated through the cross-section of the brake line, which resulted in the hydraulic fluid leak. The fatigue cracking was likely due to the detachment of the swaged compression sleeve and nut from the brake line due to exfoliation corrosion. The exfoliation corrosion likely resulted from or was exacerbated by consistent introduction of water and contact between two the different metals in the aluminum sleeve and the stainless steel brake line.

A review of the airplane's maintenance records revealed that the airplane's last annual inspection occurred about 3 months before the accident. According to the mechanic who performed the inspection, he performed a visual inspection of the brake system for looseness, leakage, and corrosion and physically checked the tightness of the "B" nut at the brake caliper in accordance with the 100-hour phase checklist; however, he did not note any problems with the left brake line.

Text from the NTSB. Open the NTSB docket for ERA14LA022 for the full record.