Accident Description
A helicopter was in normal cruise flight when it suddenly descended steeply into a shallow tidal marsh/swamp area.
Witness Accounts
Two witnesses in a boat observed the helicopter flying about 500 feet above the terrain and water. One witness reported seeing the helicopter in normal straight and level flight while over the water. The witness described the engine sound as "tinny." The helicopter suddenly turned toward land, the engine sound became quiet, and it descended rapidly to the ground. The other witness reported that his attention was drawn to the helicopter when he heard a "pop" followed by a grinding noise. He noticed that the rotors were slowing down as the helicopter dropped while in a left-hand turn or rotation.
Mechanical Examination
Examination of the rotor blades revealed evidence of low rotor energy at impact. The engine was removed from the airframe, cleaned, and then installed on an instrumented test cell where it was test run for 50 minutes at various power levels according to a factory acceptance test protocol with no abnormalities detected. Continuity was established throughout the control system, the fuel delivery system, and the drive train to the main and tail rotors.
Pre-Flight Discussion
On the day of the accident, the accident pilot's partner in the helicopter discussed an erratic fuel pressure issue with an aviation maintenance technician (AMT) at the FAA Approved Repair Station where the helicopter was parked and serviced. The discrepancy was not resolved at the time the pilot departed on the accident flight. There is no verified evidence that the pilot was aware of the discrepancy.