Helicopter Dutch Rolls and Collides with Power Lines Before Crash (N8674F)

Accident Sequence

A witness reported observing the helicopter at approximately 800 feet above the ground. Initially, the engine sounded normal. Shortly thereafter, the engine speed increased, and the helicopter began a Dutch roll—a side-to-side banking motion—for two cycles. The helicopter then rolled over one and a half times in a nose-first orientation as it descended behind trees. The aircraft subsequently collided with power lines before impacting the ground in a nose-down attitude. A post-crash fire destroyed the helicopter.

Examination Findings

Post-accident examination of the aircraft confirmed continuity of the transmission gearbox and internal rotational damage to the engine. However, there was no significant rotational damage to the main rotor, tail rotor, or the engine-to-transmission driveshaft (short shaft). The driveshaft had separated from its Bendix couplings and was crushed almost flat. No evidence of rotational damage was observed between the separated halves of the shaft. Metallurgical examination revealed that the fuel nozzle was corroded with ferrous fibers.