What happened
Following the completion of a banner-towing flight, the pilot attempted to return to a field to release the banner. During the descent toward the field, the pilot reduced power. Just before releasing the banner, the pilot increased the throttle in an attempt to arrest the descent and initiate a climb. However, at this moment, the pilot experienced little or no positive reaction from the engine.
After releasing the banner, the aircraft continued to descend. The pilot prepared for a forced landing in the field, but during the maneuver, the aircraft impacted a tree and caught fire. There were no fatalities reported in the accident.
The investigation
An examination of the engine and the aircraft revealed no mechanical anomalies. Investigators noted that the carburetor heat was in the off position. Weather data from a station approximately 6 miles north of the site recorded a temperature of 34 degrees Celsius and a dew point of 22 degrees Celsius. Based on FAA carburetor icing probability charts, these conditions were identified as being conducive to the formation of carburetor ice at both glide and cruise power settings.
Findings
- The engine failed to respond to throttle increases due to carburetor icing.
- The carburetor heat was not engaged during the period of reduced power.
- According to the FAA Pilot's Handbook of Aeronautical Knowledge, carburetor heat should be moved to the full ON position before closing the throttle and maintained during closed-throttle operations.