THE PILOT WAS PERFORMING AN AERIAL RECONNAISSANCE OF THE AREA TO BE FERTILIZER, AT 35 FEET ABOVE THE GROUND AND AN AIRSPEED OF 40 MILES PER HOUR. AT THE COMPLETION OF THE TURN TO DOWNWIND THE ENGINE LOST POWER. THE PILOT LEVELED THE HELICOPTER AND ENTERED AUTOROTATION. THE HELICOPTER LANDED HARD AND THE MAIN ROTOR STRUCK THE TAILBOOM. BOTH FUEL TANKS WERE FOUND INTACT AND A TOTAL OF 20 OUNCES OF USEABLE FUEL WAS DRAINED FROM THE TANKS. THE HELICOPTER FLIGHT MANUAL DEPICTED THE COMBINATION OF 35 FEET AND 40 MPH AS AN AREA TO AVOID CONTINUOUS OPERATIONS IN.