Rockwell International 690A N57112 accident near Ellensburg, Washington

Probable cause

The pilot’s failure to avoid a turbulent smoke column, which resulted in an overstress failure of the left aileron control rod.

NTSB analysis

The pilot reported that, while in a right turn at 7,500 feet mean sea level and above a land wildfire, the airplane entered a turbulent, dark, narrow, column of smoke. The pilot leveled the wings and continued flight through the turbulent column. When the airplane exited the column, the pilot noticed that he had to make a significant right flight control input to maintain level flight. He made a precautionary landing without further incident. Postaccident examination of the airplane revealed that the left aileron control rod was separated along the threaded portion of the shaft, about 2.5 inches from the rod end. Subsequent examination of both pieces of the aileron control rod revealed fracture surfaces consistent with overstress, with no indications of previous wear, fatigue, or corrosion. Thus, it is likely that the turbulence encountered while flying through the smoke column was sufficient to overstress the left aileron control rod.

Text from the NTSB. Open the NTSB docket for WPR12LA428 for the full record.