Accident Overview
On May 14, 2022, at approximately 1430 Pacific daylight time, a Piper PA-12 airplane, registration N3960M, was substantially damaged during an off-airport landing near Enterprise, Oregon. The pilot, who was the sole occupant, reported no injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Incident Details
The pilot reported that shortly after departing from runway 30 at Enterprise Municipal Airport (8S4), at an altitude of about 700 feet above ground level, the windshield was suddenly sprayed with oil. He immediately turned and entered the downwind leg of the traffic pattern, intending to land back on runway 30. However, during the approach, he realized he was too high and aborted the landing. On a second attempt to land on the same runway, the oil spray worsened. The pilot then flew the airplane directly onto the ground east of the airport. The subsequent impact with terrain caused damage to the fuselage.
Findings
A postaccident examination of the engine identified a loose crankshaft plug within the crankshaft. The pilot recounted that approximately 50 flight hours before the accident, another pilot flying the same airplane experienced a similar oil spray on the windshield shortly after the aircraft had undergone an annual inspection. During that inspection, the crankshaft plug had been removed and reinstalled. The airplane landed safely after the earlier incident, and it was determined that an expansion plug at the end of the crankshaft had separated, allowing oil to escape through the propeller spinner. The mechanic who performed the annual inspection reinstalled the expansion plug, and the airplane accumulated about 39 hours of flight time before the accident flight.
The Federal Aviation Administration (FAA) interviewed the mechanic and concluded that improper tools and technique were used during the reinstallation of the expansion plug. On both occasions—after the annual inspection and after the earlier oil spray incident—no record of reinstalling the expansion plug was added to the aircraft's maintenance records. Lycoming Service Instruction No. 1583, “Front Expansion Plug Replacement,” provides detailed instructions and specifies the required tooling for proper replacement of the front expansion plug.
Probable Cause
The probable cause of this accident was improper tools and technique used when reinstalling the crankshaft expansion plug.