Aeronca 11AC N86270 accident near Winchester, California

Probable cause

A total loss of engine power due to a fatigue fracture of the crankshaft.

NTSB analysis

The pilot of the tailwheel-equipped airplane reported that, while nearing his intended destination on a cross-country flight, the engine lost partial power followed by a vibration and grinding sound. The pilot attempted to restore engine power by troubleshooting; however, the engine subsequently lost total power and he initiated a forced landing to an open field. When the main wheels touched the soft terrain, the airplane nosed over, which resulted in substantial damage to the left wing.

Postaccident examination of the engine revealed metallic debris in the oil sump. The engine was disassembled by the previous owner, and the crankshaft was found fractured at the forward area of the No. 1 cylinder connecting rod journal. The entire fracture surface exhibited beach marks, consistent with high cycle fatigue over multiple duty cycles. The reason for the fatigue fracture was not determined.

The engine was last overhauled about 60 years before the accident and had accumulated about 1,569 hours of operation since overhaul. The supplied logbook excerpts consisted of 2 entries, and as such, it could not be determined what engine work was accomplished since the overhaul was performed. The engine manufacturer’s recommended time between overhauls is 12 years or 1,800 hours since overhaul.

Text from the NTSB. Open the NTSB docket for WPR24LA261 for the full record.