Accident Narrative
While initiating a hover, the pilot applied full carburetor heat. As he raised the collective for takeoff, the carburetor heat automatically reduced. The pilot then lowered the collective but reported that he "failed to get the carb heat needed to maintain power." Subsequently, the engine began to sputter and then lost power completely. The pilot performed a full autorotation into the lake.
Examination Findings
Post-accident examination of the airplane and engine found no pre-impact mechanical malfunctions. The carburetor heat control knob in the cockpit was observed to be extended approximately 2 inches, indicating it was not fully engaged.
Weather Conditions
The temperature recorded at 1655 at an airfield 25 nautical miles to the southeast was 32°F, with a dew point of 32°F and light snow and mist. A review of an FAA carburetor icing probability chart placed the reported temperature and dew point within the "serious icing at cruise power" area.