Incident Details
While en route, the pilot observed a decrease in oil pressure and subsequently shut down the engine. The airplane then conducted a forced landing in a field. During the landing flare and touchdown, the main landing gear struck a fence, and the airplane nosed over.
Post-Inspection Findings
An inspection at the accident site revealed oil covering the lower surface of the airplane, from the engine cowling to the empennage. The oil cap was not found. A mechanic who recovered the airplane from the field confirmed that the oil cap was missing and reported no discrepancies or rust on the oil filler neck.
Manufacturer Information
The engine and aircraft manufacturers had no records of a secured oil cap coming off in flight. A representative of the aircraft manufacturer stated that if the tabs inside the filler cap became corroded completely through, they would not retain the cap properly. The manufacturer’s preflight checklist includes the instruction to check the oil level. The operating details state that when replacing the cap, it must be on firmly and turned all the way to the stop at the right to prevent loss of oil through the filler neck.