ASN Wikibase Occurrence # 285192
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| Date: | Tuesday 6 March 2007 |
| Time: | 11:00 LT |
| Type: |  Enstrom F-28F |
| Owner/operator: | Private |
| Registration: | N785M |
| MSN: | 785 |
| Year of manufacture: | 1991 |
| Total airframe hrs: | 2393 hours |
| Engine model: | Lycoming HIO-360-F1AD |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Monmouth, Oregon -
 United States of America
|
| Phase: | Unknown |
| Nature: | Agricultural |
| Departure airport: | Monmouth, OR |
| Corvalis, OR | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The pilot reported that he was spraying Christmas trees, when the engine experienced an over speed condition and he "lost all power to the transmission." The pilot initiated a forced landing to a field. During the forced landing, the helicopter touched down hard and bent the tail boom. The pilot stated that the engine was producing power, but it wasn't being delivered to the rotor blades. Examination of the helicopter revealed the shaft of the main drive belt tension assembly was fractured, which resulted in the main drive belt disengaging from the transmission. Materials examination of the shaft showed that the shaft fractured due to high cycle, low stress fatigue. The fatigue initiated from multiple origins at the thread root. No material defects specific to the origin were noted, but overall hardness values suggested that the shaft strength was less than typical strength values for the specified material. It remained undetermined whether the strength was above the design minimum since no material specifications for the shaft could be produced by the manufacturer.
Probable Cause: The failure of the main drive belt tension assembly shaft due to high cycle, low stress fatigue.
Accident investigation:
 |
|
Sources:
NTSB LAX07LA106
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 01-Oct-2022 19:03 | ASN Update Bot | Added |
Corrections or additions? ... Edit this accident description
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