ASN Wikibase Occurrence # 294345
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| Date: | Sunday 21 November 2004 |
| Time: | 15:30 LT |
| Type: |  Sonex Aircraft Sonex |
| Owner/operator: | |
| Registration: | N478SX |
| MSN: | 478SX |
| Total airframe hrs: | 45 hours |
| Engine model: | Volkswagen 2180 |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Oconomowoc, Wisconsin -
 United States of America
|
| Phase: | Unknown |
| Nature: | Private |
| Departure airport: | Watertown Municipal Airport, WI (KRYV) |
| Watertown Municipal Airport, WI (KRYV) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The amateur-built airplane was damaged during a forced landing following a loss of engine power during cruise flight. The propeller and hub separated in-flight as result of a crankshaft failure. The airplane impacted a small ditch during the forced landing that resulted in the airplane nosing-over. The experimental airplane was powered by a non-certified Volkswagen 2180cc engine that was modified for aircraft use. The engine crankshaft was fractured between the oil-slinger and the retaining snap-ring groves. The fracture initiated at the aft edge of the forward keyway. The fracture features were consistent with a fatigue-type failure. The propeller and hub were not recovered during the investigation. The pilot/builder reported that he had mistakenly installed the number four (aft-most) bearing at the number two position during initial assembly of the engine. He had to remove the shrink-fit propeller hub, drive gears and spacer in order to reinstall the bearings in the correct order. The pilot/builder reported that he did not check the dimensions of the shrink-fit components prior to reassembling the engine, nor did he consult with the engine kit manufacturer on how to disassemble, inspect, and reassemble the engine components. The engine kit manufacturer did not provide the builder with engine disassembly or overhaul instructions with delivery of the engine kit. The engine kit manufacturer did not instruct builders to verify the dimensions of the shrink-fit components prior to their installation. The experimental airframe and engine did not have to comply with federal regulations required for a standard category airplane. The engine and airframe had accumulated 45.3 hours since new.
Probable Cause: The loss of engine power due to a fatigue fracture of the crankshaft. An additional cause to the accident was the pilot/builder's failure to verify the dimensions of the shrink-fit crankshaft components prior reassembling the engine. A factor to the accident was the ditch encountered during the forced landing.
Accident investigation:
 |
|
Sources:
NTSB CHI05CA032
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 11-Oct-2022 15:33 | ASN Update Bot | Added |
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