What happened
The private pilot was ferrying a Cessna 305A from Glasgow, Montana, to McAllen, Texas. After stopping at Graham, Texas, for refueling and maintenance, the pilot added oil to the engine before departing. Approximately one and a half hours after leaving Graham, the engine failed. The pilot attempted an emergency downwind landing on a farm-to-market road but struck a tree. The aircraft was destroyed, but both the pilot and co-pilot escaped without injury. VFR weather conditions prevailed at the time of the accident, and no flight plan had been filed.
The investigation
A teardown of the engine revealed that the failure was caused by a lack of lubrication. Specifically, the #6 connecting rod failed due to this oil starvation. The pilot alleged that FBO personnel at Graham had not replaced the oil filler cap after adding oil and that he did not check it during his preflight inspection.
Findings
The primary cause of the accident was the failure of the engine's #6 connecting rod resulting from a lack of lubrication. Contributing factors included the pilot's failure to verify that the oil filler cap was properly secured during the preflight inspection and the alleged failure of FBO personnel to replace the cap after servicing the aircraft.