THE PLT REPORTED THAT THE ENGINE RPM BEGAN TO DROP. SHORTLY AFTER HE TOOK OFF FROM AN OPEN FIELD. HE OPENED THE THROTTLE FURTHER IN AN ATTEMPT TO REGAIN RPM BUT THE ENGINE DID NOT RESPOND. THE HELICOPTER SUBSEQUENTLY CRASHED ONTO A BLDG ROOF AS THE PLT ATTEMPTED TO LAND WHILE AVOIDING PWR LINES AND OTHER OBSTACLES. POST-CRASH EXAM REVEALED THAT THE THROTTLE-CABLE END-FITTING HAD SEPARATED FROM THE THROTTLE CABLE PUSHROD AT THE FUEL INJECTOR SERVO. METALLURGICAL EXAM OF THE FITTING AND PUSHROD JOINING THREADS REVEALED UNEVEN WEAR THAT HAD RESULTED FROM FRETTING. SERVICE NOTICE N-196 ISSUED BY THE MFR REQUIRES INSPECTION OF THE THROTTLE CABLE FOR WEAR EVERY 100 OPERATING HRS. THE NOTICE WAS NOT COMPLIED WITH AT THE LAST INSPECTION 4 FLT HOURS BEFORE THE ACCIDENT. ACCORDING TO THE ACFT MAINT RECORDS, THE NOTICE WAS LAST COMPLIED WITH ABOUT 189 HRS EARLIER.