Incident Summary
The pilot of a helicopter reported that the accident occurred shortly after lifting off from a refueling truck during an agricultural chemical application mission. While returning to base at low altitude, the pilot observed a split in the engine/rotor tachometer. Subsequently, engine revolutions per minute (rpm) began to increase while main rotor speed began to decay.
Pilot Actions
In response to the tachometer split and the associated rotor speed decay, the pilot attempted to correct the problem through manipulation of the collective and throttle controls. Despite these inputs, the helicopter collided with the ground.
Post-Accident Examination
Following the accident, the helicopter was examined by an FAA airworthiness inspector. The inspection revealed no abnormalities with the engine, transmission, or freewheeling unit. However, heat discoloration and burned oil residue were noted on the clutch.
Conclusion
The accident sequence involved a tachometer split leading to a mismatch between engine and rotor speeds, with the pilot's control inputs unable to prevent ground impact. The cause of the tachometer split remains undetermined, and the significance of the clutch damage is not specified in the available information.