WPR12LA428

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.

On September 16, 2012, about 1600 Pacific daylight time, an Aero Commander 690A, N57112, encountered turbulence and an aileron control system failure while maneuvering above a wild land fire near Ellensburg, Washington (ELN). The airline transport pilot (ATP) sustained minor injuries, and the two passengers sustained no injuries. A precautionary landing was made at ELN after the turbulence encounter. The airplane was registered to Skystar, Inc., and operated by Courtney Aviation under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and a company flight plan was filed for the local flight that departed ELN at 1545. The pilot reported that while in a right turn around a wild land fire at 7,500 feet the airplane circled into a dark, narrow, ascending smoke column that was turbulent. The pilot quickly leveled the wings and continued to fly through the turbulent smoke column. After exiting the smoke column, the pilot noticed that the flight controls had a significant deflection to the right to keep the airplane’s wings level. The pilot elected to make a precautionary landing at ELN. After landing, the airplane was inspected, and the left aileron control rod was found separated along the threaded portion of the shaft, about 2.5 inches from the rod end. The two portions of the aileron control rod were removed from the airplane and shipped to the National Transportation Safety Board Materials Laboratory for further examination. The examination revealed no apparent wear marks along the shaft of the rod; the rod ends exhibited dirt and similar contamination. The fracture surfaces of the control rod were rough with a dull, clean luster, which was indicative of overstress. The fracture surfaces displayed no indications of fatigue or corrosion.