Beech 35-C33 N866P accident near St. George, Utah

Probable cause

The total loss of engine power due to the loose mixture control arm.

NTSB analysis

The pilot reported that, while in cruise flight, the engine’s exhaust gas temperature was hotter than normal and that the fuel flow was lower than normal. Suddenly, all engine power was lost and despite multiple attempts, he was unable to restart the engine. During the subsequent forced landing, the pilot landed the airplane gear up on a road. Postaccident examination of the engine revealed that the mixture control arm was loose on the control shaft and the nut that secured the control arm to the shaft was loose. The mixture control arm machined chamfer had formed splines and exhibited deformation and movement of material. The nut and control arm mating surfaces showed corresponding rub marks. It is likely that the loose mixture control arm and the vibration of the engine allowed for the mixture control shaft to rotate to an idle cut-off position, thus resulting in the loss of engine power. No evidence of any additional mechanical malfunctions was found during the engine examination.

Text from the NTSB. Open the NTSB docket for WPR12LA147 for the full record.