REPORTEDLY, THE PILOT EXPERIENCED A COMPLETE ENGINE FAILURE WHILE PATROLLING UTILITY LINES AT 700 FEET AGL. HE ENTERED AN AUTOROTATIVE GLIDE TO AN OPEN FIELD. THE PILOT STATED THAT HE HAD TO AVOID TREES CLOSE TO THE GROUND, AT WHICH TIME MAIN ROTOR RPM DECAYED. THE PILOT COULD NOT LEVEL THE HELICOPTER BEFORE THE TAIL ROTOR STRUCK THE GROUND. THE HELICOPTER EXAMINATION FAILED TO DISCLOSE ANY MECHANICAL PROBLEM. THE ENGINE AND ATTACHED COMPONENTS WERE EXAMINED, AND NO MATERIAL OR SYSTEM MALFUNCTION WAS DETECTED. HOWEVER, THE HELICOPTER WAS CAPABLE OF AUTOROTATING NORMALLY. THE PILOT ALLOWED THE ROTOR RPM TO DECAY BELOW A POINT WHERE HE COULD NOT RECOVER WITHOUT THE HELICOPTER SUSTAINING DAMAGE. THIS WAS THE SECOND ACCIDENT WHERE THIS PILOT WAS INVOLVED AS PILOT IN COMMAND AND AUTOROTATIVE PROCEDURES WERE IN QUESTION.