Incident Overview
During the final approach phase of a helicopter flight, the pilot reported erratic engine and rotor rpm accelerations and droop. In response to a high rate of descent, the pilot initiated a cyclic flare at 75 feet above ground level (AGL) and leveled the helicopter prior to touchdown. The helicopter subsequently landed "hard," causing the main rotor blades to flex downward. This action resulted in the separation of the tail boom from the helicopter.
Passenger Perceptions and Weight and Balance
Four passengers aboard the helicopter reported that they believed the helicopter "lost power." The helicopter was confirmed to be within its weight and balance limits for the flight.
Post-Incident Examination
An examination of the engine and fuel system did not reveal any anomalies. Calibrated bench tests of the N1 tachometer and the N2/rotor rpm dual tachometer showed that both instruments were functioning within prescribed limits. The fuel control, fuel pump, and power turbine governor were all found to be within overhaul specifications. Additionally, pneumatic lines were found to be intact.
Probable Cause
The accident investigation source does not provide a statement of probable cause.