The pilot reported that the Cessna 120 was on final approach to the airport in Gonzales, Louisiana, when the engine started to lose power.
He applied carburetor heat and switched fuel tanks, but engine power was not restored, so he made a forced landing to a field near the airport. The pilot was seriously injured.
An examination of the wreckage found that the castellated nut that connects the throttle arm to the carburetor had backed off, which allowed the engine to go to idle, and that the nut’s associated cotter pin was missing.
The pilot reported the carburetor had been replaced the day before the accident flight. The accident is consistent with the throttle arm becoming disengaged from the carburetor as a result of a missing cotter pin and the accompanying nut subsequently backing off.
Probable cause: Maintenance personnel’s improper installation of the carburetor during recent maintenance, including the omission of a required cotter pin, which resulted in a total loss of engine power.
NTSB Identification: CEN16LA033
This November 2015 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.