Incident Overview
On January 8, 2020, at approximately 1339 eastern standard time, a Hughes OH-6A helicopter, registration N6186U, was substantially damaged during an accident near Preston, Georgia. The aircraft was registered to the U.S. Department of Agriculture and operated as a public aerial observation flight. The commercial pilot and one crewmember sustained minor injuries.
Sequence of Events
The flight's purpose was to conduct aerial wildlife damage management operations. The pilot located a feral swine and informed the ground crew of its position via radio. Shortly thereafter, the pilot noted a loss of engine power and rotor rpm. The pilot maneuvered the helicopter away from trees to perform an autorotation into an open, plowed cornfield. During the landing on rough terrain, the helicopter nosed forward, and the main rotor blades contacted the ground. The engine appeared to be running at the time of impact.
Post-Accident Examination
A Federal Aviation Administration inspector examined the wreckage. The tail boom had separated from the helicopter, and three of the four main rotor blades were separated from the hub. The fuselage sustained structural damage. The operator reported that the N2 (power turbine) governor had been changed before the accident flight due to a problem encountered on a previous flight. Examination of the flight control system, drive train, main rotor system, and tail rotor system revealed no evidence of a preexisting mechanical malfunction or anomaly.
Engine and Component Testing
The engine was removed from the airframe and sent to a factory-authorized overhaul facility for further examination. Continuity was established for the N1 (gas producer turbine) and N2 rotors, which moved freely without binding or noise. Control continuity from the collective twist grip to the fuel control unit was confirmed. The control linkage to the power turbine governor was fractured at the engine firewall due to impact forces.
The engine was installed on a test stand and ran satisfactorily at takeoff power for 2 minutes, as well as at two lower power test points over a total test period of about 20 minutes. Subsequent bench testing of the power turbine governor (including the unit replaced before the accident flight), fuel control unit, fuel nozzle, and fuel pump showed all components operated satisfactorily and within manufacturers' specifications. Examination of the fuel system revealed no anomalies, and fuel lines and filters were free of contamination and obstructions. A fuel sample tested in a laboratory yielded normal results.