ASN Wikibase Occurrence # 39198
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| Date: | Wednesday 27 August 1997 |
| Time: | 09:15 LT |
| Type: |  Bell UH-1B |
| Owner/operator: | Horizon Helicopters |
| Registration: | N896W |
| MSN: | 62-4576 |
| Year of manufacture: | 1963 |
| Total airframe hrs: | 9177 hours |
| Engine model: | Lycoming T53-L13B |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Skykomish, WA -
 United States of America
|
| Phase: | Taxi |
| Nature: | Unknown |
| Departure airport: | (WA60) |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
While performing external load logging operations, the helicopter's main rotor separated from the helicopter and the helicopter crashed. Metallurgical examination of the main rotor mast revealed a fatigue fracture in the upper spirolox groove in the damper support splines. Based on the mast's historical service record, the fractured mast, a Bell part number 204-011-450-001 mast assembly with a part number '204-040-466-9' mast tube (not a valid part number according to Bell), had 4,006.7 hours at the time of the mast separation. An FAA airworthiness directive (AD), AD 97-14-12, applicable to Bell 204B, 205A, 205A-1, 205B, and 212 civil helicopters but not to surplus military UH-1 helicopters, limited the life of part number 204-011-450-001 masts to 6,000 flight hours or a retirement index number (RIN) of 300,000 (the fractured mast had a RIN of 200,335, computed according to the method specified by that AD.) The most recent main rotor mast AD directly applicable to the accident helicopter, AD 89-17-03, limited mast life to 15,000 hours and contained no requirement to establish or track RIN. The 'thin-walled' Bell part number 204-040-366-9 mast tubes installed in part number 204-011-450-001 masts were ordered removed from U.S. Army UH-1 helicopters by a 1984 U.S. Army emergency safety-of-flight message.
Probable Cause: A fatigue fracture in the main rotor mast, which resulted in an in flight separation of the main rotor from the helicopter. Contributing to the accident was insufficient Federal Aviation Administration airworthiness standards and requirements for the aircraft.
Accident investigation:
 |
|
Sources:
NTSB SEA97FA196
History of this aircraft
Other occurrences involving this aircraft
| 28 July 1992 | N89NW | Northwest Helicopters, Inc. | 0 | Hayfork, CA | |
sub |
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 24-Oct-2008 10:30 | ASN archive | Added |
| 21-Dec-2016 19:23 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 08-Apr-2024 13:13 | ASN Update Bot | Updated [Time, Other fatalities, Phase, Nature, Source, Narrative, Category, Accident report] |
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