What happened
The pilot reported that the engine RPM began to drop shortly after taking off from an open field. In an effort to regain power, he opened the throttle further, but the engine did not respond. As the helicopter descended, the pilot attempted to land while avoiding power lines and other obstacles. The helicopter subsequently crashed onto a building roof.
The investigation
A post-crash examination revealed that the throttle-cable end-fitting had separated from the throttle cable pushrod at the fuel injector servo. A metallurgical examination of the threads joining the fitting and pushrod showed uneven wear resulting from fretting. Manufacturer Service Notice N-196 requires inspection of the throttle cable for wear every 100 operating hours. Records indicated that this notice was not complied with at the last inspection, which occurred only four flight hours before the accident. According to aircraft maintenance records, the notice had been last complied with approximately 189 hours earlier.
Findings
The failure of the throttle cable connection due to fretting wear was the primary mechanical issue. The lack of compliance with the manufacturer's service notice regarding regular inspections contributed significantly to the incident. Engine power loss occurred because the pilot could not control the engine RPM effectively after the cable separation.