What happened
A pilot landed his helicopter on a bluff adjacent to a hexagonal wood frame structure that he had been constructing. While the pilot had landed at this location previously, this was the first instance where the wooden structure was in place. After landing, the pilot walked down to visit a relative, informing them that he would return later. Shortly after the pilot left the aircraft, the relative heard a loud boom followed by the sight of a fire on the bluff.
It could not be determined if the accident occurred before, during, or after a subsequent departure from the site. There were no eyewitnesses to the actual event. A post-crash fire destroyed most of the helicopter and the wooden structure. Investigators found no ground impact marks, and there was no evidence that any part of the aircraft had struck trees or dead snags at the perimeter of the bluff.
The investigation
The weather at the time consisted of light, variable winds and visual meteorological conditions. An examination of the engine, an O-360-J2A, and the remaining flight controls showed no evidence of mechanical malfunction prior to the impact.
During the wreckage inspection, investigators found that one main rotor blade had been released after the blade retention bolt failed due to shear overload. On the opposing blade, the outboard four-foot section separated from the inboard section; the inboard portion remained attached to the rotor mast and showed upward bending. A light impact impression on the top of the main rotor shaft indicated mast bumping, and the elastomeric teeter stop was missing while the opposing stop was crushed.
Findings
- The pilot had a total of 5,192 flight hours, including 772 hours in rotorcraft and 374 hours in the accident aircraft.
- An indeterminate quantity of Quinine was detected in the pilot's blood and liver during toxicological evaluation.