Amateur-built STOL CH 701 N422ES accident near Kenwood, California

Probable cause

Failure of the flywheel drive assembly, which resulted in a loss of engine power and subsequent forced landing to uneven terrain.

NTSB analysis

The pilot reported that during cruise flight, a severe vibration came from the engine, and cooling fluid leaked onto the windscreen. About 30 seconds later, the engine lost total power. The pilot made a forced landing on a narrow field, and the airplane slid off the landing area into a ditch, coming to rest nose down substantially damaging the left wing and forward fuselage.

An engine examination revealed that one of the spider pins and some of the material holding the pins, which connect three rubber links that transmit power between the engine and transmission, had broken. The semi-attached broken pin resulted in extreme vibration, it swung out on the other pin by centrifugal force which hit and broke the coolant line causing a loss of coolant and subsequent loss of engine power.

Two days after the accident, the engine manufacturer recalled the flywheel drive assemblies and stated they would be replaced with heavier flywheel drive assemblies.

Text from the NTSB. Open the NTSB docket for WPR17LA156 for the full record.