Incident Narrative
During preflight, the pilot noted an indication of 9 quarts of oil in the crankcase. The flight departed Roswell (ROW) in night VMC conditions en route to Albuquerque (ABQ). Shortly after leveling off at 6500 feet MSL, the pilot observed the oil pressure gauge fluctuating. The oil pressure then began to drop, prompting the pilot to reverse course back to Roswell. The oil pressure eventually fell to zero. The pilot reported that the engine started making unusual noises and the cockpit filled with smoke. With some power still available, the pilot executed a landing on a highway with the landing gear retracted.
Engine Examination
A post-incident examination of the engine disclosed evidence of detonation. The number 2 piston and rings were found burned, which allowed combustion gases to escape into the crankcase. The high exhaust gas pressure within the crankcase vented oil overboard, leading to oil starvation. The engine had accumulated 2053 hours of operation, with 998 hours since a major overhaul. On the morning of the incident, the engine had received a 100-hour inspection.