Primary finding
Probable cause
Connecting rod bolt fatigue.
Investigator assessment
Analysis narrative
While the airplane was in cruise flight at 500 feet agl, the engine began to vibrate and shake. The pilot shut the engine down and initiated a forced landing to an open area. During the ground roll, the airplane collided with the rough terrain and ground looped. Post-crash investigation revealed that the number three connecting rod was broken. Metallurgical examination revealed that the breaking and damage of the number three connecting rod was the result of fatigue fracture of one of the connecting rod bolts.
Source record
Factual narrative
On October 7, 1993, at 1200 Pacific daylight time, a Cessna 180K, N61946, lost engine power during cruise flight. The pilot initiated a forced landing to an open area near Garfield, Washington. During the ground roll, the airplane collided with the rough terrain and ground looped. Visual meteorological conditions prevailed at the time and no flight plan was filed. The airplane was substantially damaged and the private pilot and his passenger were not injured. The flight had originated from Spokane, Washington, on October 7, 1993, at 1100 and was en route to Grangeville, Idaho, during a personal flight. The pilot reported during a telephone interview and subsequent written statement, that while in cruise flight at 500 feet above ground level, the engine began to vibrate and shake. The pilot stated that he immediately shut the engine down and initiated a forced landing. During the ground roll on the rough terrain, the airplane ground looped before coming to a stop. During the post-crash investigation, it was found that the number three connecting rod was broken. The connecting rod and related assembly were metallurgically examined by the National Transportation Safety Board Materials Laboratory. The metallurgist reported that "The breaking and damage of the No. 3 connecting rod was the result of fatigue fracture of one of the connecting rod bolts." No metallurgical defects could be found to contribute to the initiation of the fracture. Extensive post- separation damage was noted to nearly all of the connecting rod and assembly. -