ASN Wikibase Occurrence # 39198
Last updated: 24 October 2020
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| Date: | 27-AUG-1997 |
| Time: | 09:15 |
| Type: |  Bell UH-1B |
| Owner/operator: | Horizon Helicopters |
| Registration: | N896W |
| C/n / msn: | 62-4576 |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Other fatalities: | 0 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Skykomish, WA -
 United States of America
|
| Phase: | Unknown |
| Nature: | External load operation |
| Departure airport: | (WA60) |
| Investigating agency: | NTSB |
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. CAUSE: A fatigue fracture in the main rotor mast, which resulted in an inflight separation of the main rotor from the helicopter. A related factor was insufficient FAA airworthiness standards and requirements for the aircraft.
Sources:
NTSB: https://www.ntsb.gov/ntsb/brief.asp?ev_id=20001208X08741
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] |
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