Incident Summary
A commercial helicopter flight ended with the main rotor separating in flight after the aircraft experienced mast bumping, a phenomenon associated with teetering rotor systems. The separation occurred as the aircraft was returning to base following a round-trip passenger flight, after passengers had disembarked. The accident happened during high forward speed in strong but intermittent wind conditions.
Pilot Background
The pilot was properly certificated for the flight. However, due to operator insurance restrictions, all prior commercial flights had required the aircraft's owner/operator to accompany this pilot. Consequently, this flight was the pilot's first commercial operation as the sole pilot in command.
Flight Conditions and Observations
Witnesses observed the aircraft proceeding at high forward speed in strong but intermittent wind conditions. Earlier during the same route, passengers had remarked about turbulence encountered during the flight.
Investigation Findings
Examination revealed that the main rotor separated in flight due to mast bumping. Mast bumping is a condition associated with teetering rotor systems, and the investigation determined that the envelope exceedance induced the event. Specifically, the aircraft exceeded its normal flight envelope, leading to the mast bumping and subsequent rotor separation.