Amateur-built SH2 N352GL accident near Passadumkeag, Maine

Probable cause

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

NTSB analysis

While in cruise flight, the experimental, amateur-built airplane's engine started to run "rough" and lost partial power. The pilot checked the engine gauges, noted no irregularities, and unsuccessfully attempted to restore engine power by turning the fuel boost pump on. Within about 30 seconds of the initial power loss, the engine lost total power and the propeller stopped. The pilot performed a forced landing to a bog and the airplane came to rest inverted, resulting in substantial damage to the empennage.

Disassembly and examination of the engine revealed that the crankshaft had fractured at the No. 4 cylinder journal. Further examination of the fracture surface revealed fatigue striations consistent with fatigue crack propagation. These striations were finely spaced and exhibited changing or erratic thicknesses on different areas of the fracture surface, consistent with propagation through high-cycle fatigue. The reason for the crack initiation could not be determined.

According to the engine maintenance log, the engine experienced a propeller strike during a landing incident about 5 years and 368 flight hours before the accident. The pilot elected not to have the propeller strike or sudden stoppage inspection performed, since it was not mandatory for non-certificated engines.

Text from the NTSB. Open the NTSB docket for ERA18LA190 for the full record.