Accident Narrative
A Cessna 140 was in cruise flight at 5,500 feet when the pilot felt a vibration in the engine that seemed to transmit through the entire airframe. The pilot applied carburetor heat for approximately 20 seconds. After removing carburetor heat because it did not appear to help, the engine began sputtering. The pilot reduced power and initiated a descent while attempting to troubleshoot the issue. The condition worsened, and the pilot attempted to climb but found insufficient power available. All engine gauges indicated readings within the green range, and the pilot could not recall the specific rpm reading.
The pilot and passenger began searching for a suitable landing area. During the forced landing, the airplane collided with a tree in a crevice in the mountain and then struck obstacles and rough terrain.
Meteorological Conditions
The temperature and dew point spread at 4,000 and 5,000 feet mean sea level indicated that moderate carburetor icing conditions existed at cruise power, as determined by comparison with a carburetor icing chart.
Pilot Operating Handbook Guidance
According to the pilot operating handbook for the Cessna 140, "The correct way to use carburetor heat is to first use full heat to remove any ice that is forming."
Post-Accident Examination
A post-accident examination of the engine and airframe did not reveal any mechanical malfunctions that would have resulted in a loss of power.