What happened
The pilot was properly certificated for the flight; however, due to operator insurance restrictions, all prior commercial flights had required the owner/operator to accompany this pilot, therefore this was the pilot's first commercial flight as sole pilot. Returning to base after a round-trip passenger flight, having disembarked passengers, the aircraft was observed proceeding at high forward speed in strong but intermittent wind conditions. Also, passengers remarked about turbulence along this same route of flight earlier.
The investigation
Investigation revealed the main rotor separated in flight due to mast bumping, a phenomenon associated with teetering rotor systems, induced by exceeding the normal flight envelope for the aircraft.