AT-6F N164US accident near Fitchburg, Massachusetts

Probable cause

A total loss of engine power due to a cracked carburetor float and resulting carburetor malfunction.

NTSB analysis

The pilot was performing a local, revenue sightseeing flight with a passenger in the aft seat. The flight was recorded on a glareshield-mounted personal video recorder. About 12 minutes into the flight, the pilot commented about an unspecified problem; however, the flight continued. Conversation regarding the airplane’s fuel state indicated that there was adequate fuel on board for the flight. After air work and sightseeing, the flight returned to the local traffic pattern. After turning onto final approach for landing, the engine completely lost power. The pilot was unable to restart the engine, and the airplane crashed short of the runway.

Postaccident examination of the carburetor revealed a visible crack in the soldered seam on one of the metal floats. Although there was some impact damage to the carburetor, the cracked float was located inside a fuel chamber that was undamaged. Further examination of the float fracture revealed that it was the result of a dent in the float. The fracture surface was coated with a lead-based corrosion product that was also on the inside of the float, suggesting that the crack had been open and corroding for an extended time period. It is likely that the crack in the float provided a fuel path that allowed the float to fill with fuel, resulting in a carburetor malfunction. Examination of the airplane’s records did not reveal documentation of recent carburetor maintenance.

Text from the NTSB. Open the NTSB docket for ERA11LA050 for the full record.