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| Date: | Tuesday 21 September 1999 |
| Time: | 14:05 LT |
| Type: |  Bell UH-1H Iroquois |
| Owner/operator: | Blue Mountain Helicopters, Inc |
| Registration: | N32800 |
| MSN: | 9048 |
| Total airframe hrs: | 12230 hours |
| Engine model: | Lycoming T53-13 |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Other fatalities: | 0 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Usk, WA -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | External load operation |
| Departure airport: | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The UH-1H helicopter, N32800, sustained substantial damage when it collided with terrain after a loss of control while engaged in external load logging operations near Usk, Washington.
The lower surface of the 90-degree gearbox exhibited fracture surfaces of the six attachment studs. Fretting was observed on the lower surface where the gearbox quill assembly was attached. The fracture surfaces for the six attachment studs each showed one or two relatively flat regions with smooth curving boundaries typical of fatigue. Multiple origin sites were identified on each stud, with observed ratchet marks. All of the origin areas were circumferentially aligned with the center of the gearbox, with origins on both sides of each stud, except for one stud, which had an origin area on only one side. In each case, the larger fatigue region had origins on the counter-clockwise side of the stud (as viewed from above, from the center of the gearbox).
Probable Cause: Fatigue failure of the 90-degree gearbox attachment studs, resulting in separation of the tailrotor and 90-degree gearbox from the vertical fin.
Accident investigation:
 |
|
Sources:
NTSB SEA99LA171
History of this aircraft
ex 66-16854
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 08-Mar-2024 08:05 | ASN Update Bot | Added |
| 08-Mar-2024 08:08 | ASN | Updated [Aircraft type, Cn, Nature, Departure airport, Narrative, ] |
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