N621JM

On April 19, 2019, about 1340 Pacific daylight time, a Nanchang CJ-6 airplane, N621JM, was substantially damaged when it was involved in an accident near Grass Valley, California. The pilot and passenger sustained minor injuries. The airplane was operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that, following an uneventful landing on runway 25, a 4,657 ft long and 75 ft wide asphalt runway, he extended his landing roll due to traffic on one of the taxiways. As the airplane neared the pilot's intended taxiway, he applied left rudder and lightly depressed the brake handle. About 30° into the left turn, the brakes failed, and the airplane exited the asphalt taxiway surface. Due to obstructions ahead and the down sloping terrain, the pilot applied right rudder and engine power to realign the airplane with the runway. Shortly after, the airplane overran the departure end of the runway and traveled downslope while airborne. The airplane then touched down and struck a dirt berm before it collided with a fence, nosed over, and came to rest inverted, resulting in substantial damage to the fuselage and both wings. The wreckage was recovered to a secure location for further examination.

Postaccident examination revealed that the brake cable was separated from the brake handle. The cable thimble, clevis pin, and cotter pin remained attached to the brake control handle. The separated portions of the cable were removed and sent to the NTSB Materials Laboratory for further examination.

Examination of the brake cable revealed that it was constructed of seven strands of seven metal wires (7x7). When comparing the thimble with the cable contour between two fracture locations, the fit was consistent with a thimble-eye termination created by a hand-tucked splice joint, as seen in figure 1.

Figure 1: View of the brake cable components submitted to the NTSB Materials Laboratory.

The fracture surface of the cleaned cable was examined using a scanning electron microscope. Six of the seven strands of wires exhibited relatively flat fracture surfaces normally oriented to the wire axis, consistent with a progressive fracture mechanism, such as a fatigue fracture. Only one strand and a few of the remaining individual wires showed evidence of minor elongation at the fracture location. For further information, see the Materials Laboratory Factual Report within the public docket for this accident.

No specific entries pertaining to the brake cable were found within the airframe logbook.