Aeronca 7DC N83391 accident near Ninilchik, Alaska

Probable cause

A total loss of engine power due to a shift of a crankshaft main bearing, which resulted in a lack of lubrication and subsequent overheating and failure of the engine crankshaft.

NTSB analysis

While en route during a scenic flight, the pilot noticed the engine was not making enough power for the set power setting and the oil pressure and oil temperature gauges both indicated zero. He started a climb to clear rising terrain when the engine started to vibrate violently and then the engine lost all power. The pilot made a forced landing on to a road and, after touching down, veered to avoid traffic. The airplane impacted a guardrail and nosed over, sustaining substantial damage to the fuselage and wings.

A postaccident examination of the engine revealed that the crankshaft’s No. 1 main bearing had spun, smearing metal into the crankcase and blocking the oil port. Numerous fragments of bearing material were found inside the engine. Based on the available information, it is likely that the shift of the No. 1 main bearing resulted in a lack of lubrication and subsequent failure of the engine. The reason for the bearing shift was not determined; the owner was not able to provide maintenance records for the engine.

Text from the NTSB. Open the NTSB docket for ANC23LA053 for the full record.