What happened
On October 26, 2014, at approximately 0830 Pacific daylight time, a Cessna TU206G, registration N4776U, veered off a gravel runway and collided with a ditch at a private airfield near Monument, Oregon. The flight departed from Monument Municipal Airport about 15 minutes earlier. The pilot, a commercial pilot and the sole occupant, was not injured.
The pilot reported that the aircraft touched down on the gravel runway at a slow groundspeed. Following touchdown, the airplane began to veer toward the right. The pilot attempted to regain directional control using aileron inputs and the brakes, but the aircraft continued off the right side of the runway. The aircraft eventually struck a tree with the right wingtip and collided with a ditch, coming to rest in an inverted position. The aircraft sustained substantial damage to the wings and tail section.
The investigation
Recovery personnel observed that the left tire left a long track in the gravel that angled to the right before dropping off the runway edge. While skid marks in the crushed rock indicated the left brake was functional, the loose and deep nature of the gravel surface prevented effective traction. The nose wheel dug a trough in the surface, while the right wheel appeared to be airborne for much of the landing roll.
An FAA inspector examined the disassembled braking system. The inspection found that both brakes were intact and both tires rotated freely. Although the inspector could not operate the brakes using the pedals, it was impossible to determine if this failure was caused by the accident itself or the subsequent recovery process.