THE PILOT AND TWO PASSENGERS WERE PATROLLING ALONG THE WEST'SIDE OF A POWER LINE FROM SOUTH TO NORTH. WHILE PATROLLING THE PILOT WAS MAINTAINING AN ALTITUDE OF 75 TO 100 FT AGL AT 20 TO 30 KTS WITH AN 8 TO 10 KT TAIL WIND. HE REPORTED THAT HE WAS DESCENDING DOWN A RIDGE WHEN THE HELICOPTER BEGAN A SLOW YAW TO THE RIGHT. HE STATED THAT FULL LEFT PEDDLE WAS USELESS AND THE HELICOPTER CONTINUED TO YAW TO THE RIGHT. HE REDUCED THE COLLECTIVE TO CONTROL THE RATE OF THE TURN, BUT BEGAN DESCENDING TOWARD THE WIRES. HE THEN INCREASED THE COLLECTIVE AND ADDED RIGHT CYCLIC TO AVOID THE WIRES. AFTER SPINNING 2 OR 3 TIMES, HE REDUCED THE POWER AND COLLECTIVE AND BEGAN AN AUTOROTATIVE LANDING. DURING THE LANDING, THE HELICOPTER TOUCHED DOWN HARD IN A WOODED AREA. A POST IMPACT FIRE DESTROYED THE FUSELAGE FROM STATION 164 FORWARD.