What happened
During cruise flight, the pilot of a twin-engine aircraft noticed that the trim wheel had rotated almost 360 degrees from its original position. The wheel then stopped and rotated 180 degrees in the opposite direction, though no changes in pitch attitude were observed. Following this movement, the pilot experienced a strong vibration moving forward and aft through the yoke, accompanied by a clacking sound.
In response to the mechanical issues, the pilot feathered both engines. The flight subsequently resulted in a forced landing following the loss of stabilator trim control.
The investigation
An examination of the stabilator trim tab control rod was conducted. Investigators found evidence of internal corrosion within the rod. Further analysis revealed that this corrosion had reduced the thickness of the load-carrying area of the stabilator trim tab control rod.