ASN Wikibase Occurrence # 45138
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| Date: | Friday 25 July 2003 |
| Time: | 17:03 |
| Type: |  Kaman K-1200 K-Max |
| Owner/operator: | U.S. Department of Interior (Bureau Indian Affairs) |
| Registration: | N314KA |
| MSN: | A940015 |
| Year of manufacture: | 1996 |
| Total airframe hrs: | 4583 hours |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | Keller, WA -
 United States of America
|
| Phase: | En route |
| Nature: | Fire fighting |
| Departure airport: | Keller, WA |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The pilot was returning to pick up a load of water while engaged in firefighting operations. The helicopter was in cruise flight when the pilot radioed "I've got a problem" and "I'm going down." Witnesses observed rotor blades departing from the helicopter. On site examination revealed that all four main rotor blades had departed from their respective rotor hub/blade grip units coming to rest in a circumferential band within several hundred feet of the helicopter's ground impact point. Both main rotor hubs also departed the airframe and were located a short distance north and east of the ground impact site. Post crash examination revealed the presence of extensive corrosion fatigue cracking in the upper half of the blade grip plate associated with blade (s/n) 27B. The crack passed through the 7th blade retention bolt hole from the inboard section of the grip leaving the blade attached at the upper blade grip plate by one bolt inboard of the crack and 5 bolts outboard of the crack. The crack displayed corrosion fatigue striations through most of its surface. The number 7 blade retention bolt bushing was also found to have corrosion fatigue cracking in line with the grip crack. With a crack through the inboard section of the upper blade grip plate occurring, the rigidity of the associated blade (27B) would have been significantly weakened in the vertical axis and dynamic imbalance would have developed leading to successive separation of all four blades.
Probable Cause: Corrosion fatigue within the blade retention bolt bushing(s) of the main rotor blade grip resulting in fatigue, cracking and ultimate separation of the upper grip plate. The separation of the upper blade grip plate led to a dynamic imbalance within the rotor system and the subsequent loss of all four rotor blades in flight.
Accident investigation:
 |
|
Sources:
NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20030730X01223&key=1
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 28-Oct-2008 00:45 | ASN archive | Added |
| 07-Aug-2010 08:35 | Alpine Flight | Updated [Time, Aircraft type, Cn, Other fatalities, Nature, Source] |
| 02-Sep-2014 11:28 | Aerossurance | Updated [Nature, Source, Narrative] |
| 21-Dec-2016 19:24 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 08-Dec-2017 18:55 | ASN Update Bot | Updated [Cn, Nature, Destination airport, Source, Narrative] |
| 12-Nov-2022 02:55 | Ron Averes | Updated [Operator] |
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