Incident Overview
A Cessna 172M aircraft suffered a loss of engine power and subsequently collided with uneven terrain during the landing phase. The event occurred while the airplane was operating in conditions described as prevalent to fuel vaporization ice within the induction system.
Pilot Report
According to the pilot, the airplane was cruising at approximately 9,500 feet above mean sea level (MSL), which equated to about 1,500 to 2,000 feet above ground level (AGL). The outside air temperature was 40 degrees Fahrenheit. The pilot noted that the carburetor heat control was in the 'off' position when the engine began to run roughly. He then moved the carburetor heat handle to the 'on' position, which caused the engine to run even more roughly. Subsequently, he returned the carburetor heat to the 'off' position, and the engine continued to run roughly before eventually stopping completely.
Weather Conditions
A weather observation facility located 45 nautical miles to the northwest of the accident site reported a temperature-dewpoint spread of 25 degrees Fahrenheit, corresponding to a relative humidity of approximately 40%. These conditions are within the potential range for carburetor ice formation.
Aircraft Manual Guidance
The aircraft flight manual provides a procedure for clearing carburetor ice: apply full throttle, pull the carburetor heat knob fully out until the engine runs smoothly, then remove carburetor heat and readjust the throttle.