Piper PA-12 N3960M accident near Enterprise, Oregon

Probable cause

The inadequate maintenance and inspection of the crankshaft expansion plug, which resulted in the separation of the expansion plug from the crankshaft and the subsequent loss of oil and windshield obstruction during departure.

NTSB analysis

The pilot reported that shortly after departure, about 700 ft above ground level (agl), the windshield was sprayed with oil. He turned and entered the downwind leg of the traffic pattern and attempted to land on the runway. He reported that he was too high during the approach and aborted the landing. On the second attempt to land on runway 30, the oil spray was getting worse, and the pilot made a precautionary landing resulting in substantial damage to the fuselage.

The postaccident examination of the airplane and interview with the mechanic revealed that the expansion plug was improperly installed and had separated from the end of the crankshaft, causing oil to exit through the propeller spinner resulting in the oil spray on the windshield.

Text from the NTSB. Open the NTSB docket for WPR22LA177 for the full record.