Incident Overview
A pilot initiated the engine start sequence of a helicopter while one of the main rotor blades was secured with a tie-down. As the engine accelerated, the pilot observed that the main rotor blade was not rotating. In an attempt to abort the start, the pilot took action, but at that moment the helicopter unexpectedly 'jumped into the air and yawed violently,' as described in the investigation report.
Damage and Sequence
The main rotor blade fractured during the event, and the tie-down hook attached to the end of the blade was straightened. The rear cross tube of the landing gear was driven into the lower fuselage, puncturing the fuel tank and causing it to rupture.
Pilot's Statement
The pilot reported being distracted by thoughts about the impending flight prior to the incident.
Findings
The investigation determined that the engine was started while a main rotor blade was still tied down, which prevented the rotor from turning and led to the structural failure and subsequent movement of the helicopter.