Incident Description
During flight at approximately 500 feet above ground level, the helicopter experienced a loss of engine power. The pilot initiated an autorotative landing and issued a mayday call. The helicopter descended toward a marshy area characterized by grass 4 to 5 feet in height. Upon touchdown, the landing was hard, causing the main rotor blades to flex downward and sever the tail boom.
Investigation Findings
An investigation into the power loss revealed that the splines on the fuel pump drive shaft, part number 102-1416-01, had worn to a degree where they no longer engaged the spline adapter. This disengagement resulted in the fuel pump ceasing to operate, leading to the engine power loss. The investigation further noted that all applicable inspections had been complied with, with the most recent inspection occurring 205 flight hours prior to the accident.
Probable Cause
The probable cause of the engine power loss was the wear of the splines on the fuel pump drive shaft, which prevented engagement with the spline adapter.