What happened
Just prior to lift-off, a significant vibration accompanied by lateral rocking occurred in the helicopter. Although the pilot brought the power to idle immediately, the aircraft had already started to come apart.
The investigation
During the examination of the engine and rotor system, it was determined that ground resonance had occurred. This condition was attributed to the main rotor dampeners being under-torque. Notably, these dampeners had been serviced just 1.5 hours prior to this accident.
Findings
The primary factor contributing to the incident was the improper torque on the main rotor dampeners. The mechanical failure led directly to the structural disintegration of the aircraft during the critical takeoff phase.