ASN Wikibase Occurrence # 40827
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| Date: | Wednesday 21 May 1997 |
| Time: | 10:51 LT |
| Type: |  Hiller UH-12E |
| Owner/operator: | Blue Mountain Aviation |
| Registration: | N3005J |
| MSN: | 5024 |
| Total airframe hrs: | 4196 hours |
| Engine model: | Lycoming VO-540-C2A |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Miltonfreewater, OR -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | Agricultural |
| Departure airport: | Walla Walla, WA |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
A witness reported that as he was watching the helicopter maneuver for the aerial application flight, one of the main rotor blades separated from the helicopter. The helicopter then nosed down and collided with the terrain. Examination of the separated sections of the main rotor blade found that the origin area contained a few crack arrest positions and small ratchet marks, indicating that fatigue cracking initiated from multiple locations. The thickness of the larger spar was measured and found to be slightly below the specified manufacturer's measurements. Scratches or scoring marks, similar to a sanded appearance, were noted on the lower surface where the thickness was reduced. The thickness of the spar wall continued to decrease further outboard of the fracture. Corrosion was also visible. The applicable Airworthiness Directive (AD) requires performance of inspections per the Service Bulletin (SB) to prevent main rotor blade failure due to cracking of the spar or delamination of the trailing edge skin from the spar. The SB specifies the different types of inspections to be accomplished, the intervals for accomplishment of the inspections, and how the inspections are to be performed to detect for cracks or delamination. The SB indicates that a chemical compound is to be used to strip the paint from the surface to accomplish the inspection. Maintenance records indicate that inspections were performed, however, no cracks were detected.
Probable Cause: The main rotor blade separated due to fatigue. Factors were: an Airworthiness Directive was not properly performed, and inadequate inspection of the main rotor blades.
Accident investigation:
 |
|
Sources:
NTSB SEA97LA117
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 15:24 | ASN Update Bot | Updated [Time, Other fatalities, Departure airport, Source, Narrative, Category, Accident report] |
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