Beech G35 N4401D accident near Surprise, Arizona

Probable cause

The mechanic's failure to properly secure the bolt connecting the throttle cable to the carburetor during the installation of the carburetor, which resulted in a loss of engine power.

NTSB analysis

The flight instructor was asked to complete a maintenance test flight of the airplane following the installation of a repaired carburetor. He elected to use the flight to provide instruction to the private pilot who had requested a checkout in the airplane. The private pilot reported that the flight was initially normal, but then the engine stopped responding to throttle control. According to the private pilot, the engine remained at idle power as the airplane descended and impacted trees in a residential area.

Examination of the wreckage revealed that the carburetor throttle cable was detached from the throttle body linkage. The bolt and castellated nut used to secure the throttle cable to the linkage were found lying separately in the engine cowling; there was no evidence that a cotter pin had been used to secure the nut on the bolt, as required.

It is likely that the loss of engine power resulted from the failure of the mechanic who installed the carburetor to install the cotter pin when he attached the throttle cable to the carburetor. During the maintenance test flight, the castellated nut backed off of the bolt, which resulted in a loss of throttle control.

Text from the NTSB. Open the NTSB docket for WPR16FA102 for the full record.