NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The commercial pilot reported that, while in cruise flight, he noticed that the engine oil pressure had dropped. He declared an emergency and was initially given a heading to the closest airport. About 2-3 minutes later, he heard rattling noises from the engine, then the cabin filled with black smoke. He identified an open field and maneuvered for a forced landing. The airplane hit a berm and bounced, hitting several more berms, until it came to rest inverted. On-scene photographs showed that the belly of the airplane was coated with engine oil aft of the engine firewall. An engine examination identified that the air-oil separator return line was not connected to the return port located on a cylinder rocker cover. Maintenance records showed that the pilot had performed an oil change 4.3 hours before the accident. Since the oil filter is located behind the air-oil separator return line, it is likely that the pilot removed the air-oil separator return line to access the oil filter and failed to reconnect the line after replacing the filter. While in flight, oil slowly drained out of the air-oil separator return line and open return port, coating the belly of the airplane, until the engine experienced catastrophic failure due to oil starvation.