Incident Overview
During wildlife control operations, a helicopter experienced a catastrophic engine failure at an altitude of 40 feet above ground level. The pilot attempted to regain engine power by performing a technique described as "milking the collective." Subsequently, the helicopter impacted the ground in a level attitude without flaring. Following the initial impact, the helicopter bounced 13 feet forward and rolled onto its right side.
Engine Examination
A detailed examination of the engine revealed that the #3 cylinder connecting rod cap bolts had fractured, resulting in a catastrophic failure of the bearing cap and piston. The safety board conducted a metallurgical examination of the fractured bolts.
Metallurgical Findings
The metallurgical examination indicated that the fracture features at the center of each bolt were the result of overstress separations. However, the fracture features adjacent to the outside diameter of each bolt contained mechanical damage that obliterated the original fracture features.