Accident Sequence
While on final approach at approximately 300 feet above ground level, the airplane's ailerons became locked, preventing the pilot from returning the aircraft to level flight. The airplane, with landing gear and flaps retracted, entered a left spiral and completed two full 360-degree turns before impacting a wheat field.
Investigation Findings
Examination of the control system revealed that a brass alloy foreign object had entered the interior of the control wheel through an open inspection window located on the back side of the single throwover type control yoke. The foreign object became trapped between the sprocket and the chain, effectively locking the ailerons in a position that caused the spiral descent. The object was not recovered during the investigation.
Aircraft Configuration
At the time of the event, the landing gear and flaps were retracted, as the pilot had configured the aircraft for the descent. The control yoke was of a single throwover type, commonly found in some light aircraft designs.