During the takeoff, about 20 feet above the hilltop helipad, the pilot "felt a downdraft hit the helicopter." He stated that he corrected with a collective input, but "got low rpm," and responded with collective and cyclic control inputs. The helicopter descended and impacted the down-sloping hillside, and came to rest on its side, which resulted in substantial damage. When asked if there were any mechanical problems with the helicopter prior to the accident, the pilot stated, "No, it was perfect." Review of performance documents in the Pilot's Operating Handbook revealed that the helicopter was loaded 94 pounds above the manufacturer's maximum gross weight and 120 pounds above the maximum allowable gross weight for out of ground effect hover maneuvers for the environmental conditions present at the time of the accident.