Engine Failure Due to Incorrectly Installed Circlips During Overhaul (N7162M)

Incident Narrative

The pilot reported that the helicopter was in cruise flight at an altitude of about 75 feet above trees, having just completed a swath run. At that moment, the engine ceased operation. The pilot initiated a right turn and subsequently entered autorotation. He acknowledged that he did not monitor either the engine rpm or the rotor rpm during this sequence. As the helicopter descended to approximately 30 feet above ground level, the pilot began a deceleration and pulled all collective pitch. The helicopter then made a hard impact with the ground. The impact caused the main rotor blades to collide with the tailboom assembly, resulting in damage.

Engine Examination Findings

Post-accident examination of the engine assembly focused on the components related to the power loss. The investigation revealed that 10 out of 22 circlips had been installed incorrectly during a prior engine overhaul. This incorrect installation directly resulted in the failure of the number 5 connecting rod. The failure of the connecting rod led to a loss of engine power, which precipitated the forced landing and subsequent ground impact. The circlips were intended to secure components within the engine, and their misinstallation prevented proper retention.