Accident Description
A pilot conducted a preflight inspection of an airplane and checked the engine oil level by removing the dip stick/oil filler cap. After approximately 10 to 15 minutes of flight, the pilot observed a decrease in torque indication and engine oil pressure. The pilot decided to return to Dillingham. En route, the engine lost further oil pressure, coughed twice, and the pilot feathered the propeller before executing a landing on the tundra. During the landing, the airplane nosed over.
Findings
An on-site inspection revealed that the left, lower side of the fuselage was covered with oil. The oil dip stick/filler cap was not installed in the filler neck; it was found resting on the inside of the upper cowling, which was accessible only because the airplane was inverted. A review of records indicated that the pilot's certificate was listed in the computer database as an Airline Transport Pilot (ATP) certificate, because the database program does not accept a Commercial Pilot rating when a scheduled 14 CFR 135 passenger/cargo operation is shown. However, the pilot actually holds only a Commercial Pilot certificate.