Accident Details
A pilot was making an approach for landing at a field site when the helicopter experienced a partial loss of engine power. The pilot lowered the collective and rolled the throttle to the full on position. Subsequently, the helicopter collided with power lines and then the ground.
Investigation Findings
Review of the aircraft log books revealed that the last annual inspection had been completed three months before the accident. The carburetor installed on the helicopter was not approved for use by the Franklin Engine Company. Examination of the carburetor heat control valve revealed an incorrect spring had been installed, which rendered the carburetor heat inoperable from the cockpit.
Weather Conditions
A carburetor icing probability chart indicated the possibility of carburetor icing conditions based on the weather at the time of the accident.
Pilot Actions
Prior to the approach, the pilot had completed the before-landing check without the aid of a checklist, and the carburetor heat was not turned on.