What happened
The pilot was operating the aircraft during the downwind leg of the traffic pattern when he reduced power settings. He stated that he applied carburetor heat prior to this reduction in power. Shortly after applying the heat, the engine RPM decreased significantly. When the pilot attempted to regain RPM by adjusting the throttle, the engine stopped completely.
The pilot reported attempting to restart the engine but was unsuccessful. Consequently, he initiated a forced landing at an area near the airport. During the approach for this forced landing, the aircraft collided with trees. The pilot noted that the engine operated normally after the accident when carburetor heat was toggled on and off.
The investigation
Post-accident inspection revealed that the aircraft sustained substantial damage to the structure during the collision with the trees. No mechanical anomalies were found that would have precluded normal operation of the engine prior to the impact, aside from the carburetor ice issue identified by the pilot's account.
Findings
The investigation determined that the primary factor leading to the accident was the pilot's decision to apply carburetor heat while the engine was at a low power setting. This action resulted in carburetor ice formation, which caused the engine to lose power and eventually stop. The subsequent loss of control during the forced landing led to the collision with trees.
Safety message
Pilots should be aware that applying carburetor heat at low power settings can induce carburetor ice if conditions are conducive, potentially leading to engine failure. Carburetor heat should typically be applied before reducing power or when icing conditions are suspected during normal operation.