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.
The mechanic should have went back to the aircraft after signing off the logs and re-inspect the work that he or she had done. A second look over the work is the best action to do at that time.
Never get in a hurry to leave the job even if you wife or girl friend are standing there waiting on you for the dinner date.
In the manufacturing industry the use of a dedicated inspection department is to assure the adequacy of the work was done.
“In the manufacturing industry the use of a dedicated inspection department is to assure the adequacy of the work was done.” Yep, and significant errors are STILL allowed to slip through. That’s why after an engine change (no matter whether factory new, factory reman, or field overhaul) it’s a REALLY bad idea to launch on a night IMC flight until 10-20 hours are on the engine. Lots of accident reports discuss engine infant mortality. Some engine “SID” events don’t happen until 100 hours or more have elapsed. For example, the OH shop that used blue Permatex gasket material to mate the sides of an engine… contrary to the engine maintenance and assembly instructions. Or more recently, the failures that brought to light Lycoming’s pushrod tube problem which eventually resulted in an emergency AD. There ain’t no silver bullets in maintenance, just silver plated ones.
The pilot joined the 20% club… you know, the select group of GA pilots who crash because of a maintenance error. Bummer. It looks like the pilot attempted to do almost everything right… the carb was factory overhauled, the removal/installation was done by an FAA certified A&P/IA; the work was entered into the aircraft logs; there was a post installation engine run and followup inspection which determined all was happy. The pilot conducted a post maintenance flight the day after the carb was replaced. There isn’t much more the pilot can do in these circumstances except do owner assisted annuals/maintenance (plus be VERY alert for mechanic errors), do a long test flight NEXT to the airport – ALWAYS within gliding distance, and (probably most important of all) be proficient with emergency procedures – especially “system malfunction – power plant” off airport landings. Kudos to the pilot. Unfortunately, his 25 minute post maintenance flight was at low level (900-1000′ AGL) and beyond gliding distance to a good landing site.