N93876

On April 12, 2010, about 1130 eastern daylight time, a Univair Aircraft Corporation 415-C, N93876, piloted by a private pilot, exited runway 18 (1,400 feet by 80 feet, dry grass) while landing at private airstrip near Columbiaville, Michigan. The airplane subsequently sustained substantial damage on impact with terrain. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flight was not operating on a flight plan. The pilot was uninjured. The flight originated about 1100 from the Wm 'Tiny' Zehnder Field Airport, near Frankenmuth, Michigan, and was destined for the private airstrip.

The pilot, in his accident report, said he'd set up for a normal approach to runway 18 and landed approximately a third of the way down the runway. He said that as he applied the brakes near the turnabout area at the south end of the runway, he discovered that he couldn't stop. He went off the end of the runway and down an embankment causing considerable damage to the airplane. The pilot said that "later when the FAA [Federal Aviation Administration] inspector arrived, we discovered that the brake pedal had broken ..."

An examination of the brake master cylinder piston rod’s clevis was found separated from its piston rod. The separated clevis was retained by the FAA inspector and forwarded to the National Transportation Safety Board (NTSB) for further examination at the materials laboratory.

A Senior Materials Engineer examined the separated clevis and reported that the fracture surface had rough matte gray fracture features consistent with an overstress fracture. Their report stated that overall fracture features including radial marks and contact faces that were consistent with fracture under bending loads with the upper end bending forward and to the right relative to the lower end. No evidence of any preexisting damage such as fatigue was observed.