ASN Wikibase Occurrence # 45016
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| Date: | Thursday 20 November 2003 |
| Time: | 15:45 |
| Type: | Kaman K-600 |
| Owner/operator: | JC Helicopter Services, LLC. |
| Registration: | N286M |
| MSN: | 60-286 |
| Year of manufacture: | 1962 |
| Total airframe hrs: | 6435 hours |
| Engine model: | Lycoming T-53-L-13 |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Nordman, ID -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | External load operation |
| Departure airport: | Priest Lake, ID |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
While ascending in a hover to take the slack out of a long-line, the Part 137 logging helicopter experienced the complete failure of its right main rotor mast (shaft). An NTSB metallurgical inspection determined that the mast had failed due to the propagation of a fatigue crack that originated on the inside surface of an opening in the shaft wall (L-crank slot). The fatigue crack originated in two shallow corrosion pits (0.0033 and 0.0029 of an inch wide) on the inner surface of the L-crank slot. Although the shaft had been overhauled/inspected approximately 1,000 hours prior to the accident (1,200 hour interval), the Military Technical Order that regulates the overhaul of this mast does not address a specific inspection for corrosion, nor how to address any corrosion that is detected.
Probable Cause: The total failure of the helicopter's right main rotor shaft while in an ascending hover due to the propagation of a fatigue crack that initiated in a corrosion pit on the surface of a slot in the wall of the subject shaft. Factors include accumulation of corrosion on the surface of the shaft.
Accident investigation:
 |
|
Sources:
NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20031212X02029&key=1
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 28-Oct-2008 00:45 | ASN archive | Added |
| 21-Dec-2016 19:24 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 08-Dec-2017 20:21 | ASN Update Bot | Updated [Operator, Nature, Source, Narrative] |
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