What happened
During the cruise phase of flight, the aircraft began an unexplained shallow left turn. The pilot attempted to counteract the movement by moving the yoke both left and right, but these inputs had no effect on the increasing left bank angle. The unintended turn continued for three complete revolutions, with the bank angle becoming progressively steeper. Upon completion of the third turn, the aircraft's pitch transitioned to a vertical nose-down position, leading to an impact with trees and terrain. The accident resulted in fatal injuries.
The investigation
Investigators examined the aileron control cable circuit to determine the cause of the loss of control. They discovered that the inboard end of the right aileron upper cable was missing its eye splice and thimble. The cable exhibited an approximately 90-degree bend at the location where the eye had been, which was consistent with deformation from an eye loop. There was no evidence of kinking or heavy rubbing at the separation point.
Further analysis of the remaining sleeve (nicropress) on the right aileron upper cable revealed that it did not meet the manufacturer's specified crimp dimensions. Additionally, tooling marks on the sleeve were inconsistent with the use of the required installation tool. Testing demonstrated that while a properly installed eye splice should cause the cable to fracture before pulling out of the sleeve, this specific cable failed prematurely. While the specified limit load for these cables was 2,000 pounds, the remaining eye splice on the right aileron upper cable pulled out of its sleeve at only 476 pounds. For comparison, the other five tested eye splices held more than 1,600 pounds before the cables themselves failed.
Findings
A review of the aircraft maintenance logbooks showed no specific records regarding the replacement of aileron control cables. However, due to the inconsistent appearance and characteristics of the various aileron cable sleeves, investigators concluded it was likely that the nonconforming sleeves were not original manufacturer components.