Kenwood, CA, USA
N422ES
SIMMONS GARY F STOL CH 701
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.
On July 15, 2017, about 1140 Pacific daylight time, an experimental, amateur-built STOL CH-701 airplane, N422ES, was substantially damaged when it was involved in an accident near Kenwood, California. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot, who also owned the airplane, reported that he departed from Cloverdale Municipal Airport (O60), Cloverdale, California, and was destined for Sonoma Skypark Airport (0Q9), Sonoma, California. While in cruise flight, he felt a severe vibration from the engine and saw cooling fluid leaking onto the windscreen. About 30 seconds later, the engine lost total power. The pilot conducted a forced landing on a narrow field surrounded by vineyards. During the landing, the airplane slid into a ditch on the side of the field and came to rest nose down substantially damaging the wing and forward fuselage. The pilot reported 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. Two days after the accident, Viking Aircraft Engines, the engine manufacturer, noted the forced landing due to a failed flywheel drive part, recalled the flywheel drive assemblies, and stated they would be replaced with heavier flywheel drive assemblies. About 130 engines were potentially affected.
Failure of the flywheel drive assembly, which resulted in a loss of engine power and subsequent forced landing to uneven terrain.
Source: NTSB Aviation Accident Database
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