# NTSB WPR17LA156: Simmons Gary F Stol CH 701, N422ES, Kenwood, CA, July 15, 2017

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Class 3 · Limited · Final report
- Date: July 15, 2017, 11:40 local (18:40 UTC)
- Place: Kenwood, CA
- Coordinates: 38.414443, -122.54528 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=38.4144&lon=-122.5453&mi=10
- Phase of flight: [Emergency descent](https://openairdocs.org/ntsb-phases/600) (OpenAirDocs' grouping)
- Defining event: [Emergency descent: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed
- Report: Approved by Office Director
- Investigation class: Class 3
- NTSB office: Western Pacific Region
- Parties: Federal Aviation Administration
- NTSB case key (mKey): 95595
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR17LA156
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95595/pdf
- Page: https://openairdocs.org/ntsb/WPR17LA156

## Probable cause

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

## Findings

NTSB's coded findings; those marked are part of the probable cause.

- [Engine (turbine/turboprop)](https://openairdocs.org/ntsb-findings/01057200): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Simmons Gary F STOL CH 701, 1 case](https://openairdocs.org/ntsb-findings/01057200/cases.md?model=05629Z3), [All aircraft, 67 cases](https://openairdocs.org/ntsb-findings/01057200/cases.md)

## Sequence of events

The events NTSB coded, in order, by phase of flight. The defining event best describes what happened.

- [Emergency descent: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Simmons Gary F STOL CH 701, 1 case](https://openairdocs.org/ntsb-events/341/sequence.md?model=05629Z3), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md)
- [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Simmons Gary F STOL CH 701, 1 case](https://openairdocs.org/ntsb-events/440/sequence.md?model=05629Z3), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md)

## 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.

## Factual narrative

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.

## Aircraft

- Registration: [N422ES](https://openairdocs.org/aircraft/N422ES), registered now, S/N 7200 (OpenAirDocs)
- Reported make and model: SIMMONS GARY F STOL CH 701 (NO SERIES)
- Registry model: [Simmons Gary F STOL CH 701](https://openairdocs.org/model/simmons-gary-f-stol-ch-701) (registry code 05629Z3) (OpenAirDocs)
- Registry engine: [Viking 110](https://openairdocs.org/engine/viking-110) (registry code 63700, reciprocating) (OpenAirDocs)
- Category: Airplane, amateur-built
- Serial number: 7200
- Year built: 2010
- Airframe hours: 450
- Engines: VIKING 110 110 horsepower reciprocating
- Damage: Substantial damage
- Flight: Personal, Part 91
- Airworthiness certificate: Special, Experimental (Special)
- Last inspection: Condition, May 20, 2017, 14 hours before
- Departed: O60, CLOVERDALE, CA
- Destination: 0Q9, SONOMA, CA
- Equipment: Electronic flight bag or handheld device, Auto-pilot, Airframe parachute, Onboard weather, Handheld GPS

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 75; injuries: none; sport pilot; airplane ratings: single-engine land; last flight review May 4, 2017; seat: left; restraint: 3-point; flight hours: 1,900 total, 1,520 in this make and model, 1,880 as pilot in command, 20 in the last 90 days, 10 in the last 30 days, 1 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 230° at 4 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 81 °F, dew point 57 °F
- Altimeter: 30.00 inHg
- Observed at: KAPC, 17 nm away

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 20170715009949A](https://openairdocs.org/incident/20170715009949A), Jul 15, 2017: Simmons Gary F STOL CH 701, Glen Ellen, CA, Substantial damage. N422ES, experimental stol ch 701, crash landed in a field due to mechanical issues with the engine. Substantial damage, no injuries.

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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