NTSB Identification: SEA97LA117.
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Accident occurred Wednesday, May 21, 1997 in MILTONFREEWATER, OR
Probable Cause Approval Date: 04/24/1998
Aircraft: Hiller UH-12E, registration: N3005J
Injuries: 1 Fatal.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
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.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: 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. Full narrative available
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