The helicopter pilot reported that, after landing, while hover taxiing and turning right onto the taxiway, the helicopter continued the right turn and drifted off the taxiway. He applied full left pedal to no avail, so he closed the throttle to perform an autorotation to decrease the speed of rotation, also to no avail. He added collective to reduce the rate of descent, but the helicopter landed and slid into a drainage ditch, the main rotor blades impacted a berm near the taxiway, and the helicopter came to rest on its side against the berm.

The helicopter sustained substantial damage to the fuselage.

The pilot reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation.

The pilot reported the wind was from 320° at 11 knots, gusting to 16 knots. The pilot landed the helicopter on runway 04 and was turning to the right.