Stinson 108-3 N121CM accident near Beaumont, Texas

Probable cause

The lack of a forward clamp on the carburetor heat box rubber boot, which allowed the boot to be ingested into the inlet of the carburetor heat box, restricting the airflow and leading to a subsequent partial loss of engine power.

NTSB analysis

The pilot reported that the airplane's engine lost partial power shortly after takeoff. The airplane was unable to maintain altitude, so he executed a forced landing to a field, and the airplane nosed over. Postaccident examination revealed that the rubber boot between the carburetor heat box and cowl was missing its forward clamp, which was not found in the wreckage The clamp was likely missing because an improper clamp was used or a clamp was not installed properly, which allowed the boot to come loose and to be ingested into the inlet of the carburetor heat box, restricting the airflow and resulting in a rich fuel mixture and the subsequent partial loss of engine power. No other anomalies were found with the engine or its systems.

Text from the NTSB. Open the NTSB docket for CEN13LA305 for the full record.