What happened
During the landing roll, the pilot reported that the aircraft began to veer toward the left. After determining that aileron and rudder controls were ineffective at re-aligning the aircraft's direction of travel, the pilot transitioned to using the nose wheel steering control. While applying corrective input to the far right, the pilot heard a "clink" sound. The aircraft subsequently exited the side of the runway and collided with the terrain.
The investigation
A post-accident inspection of the aircraft revealed that the nose wheel steering cable was broken. The cable was submitted to the National Transportation Safety Board Materials Laboratory for detailed examination.
Laboratory specialists found that the ends of many wires within the cable exhibited fractures on a flat plane perpendicular to the longitudinal axis, which is characteristic of a fatigue crack. Approximately 90 percent of these flat areas extended through the fracture face. Furthermore, the metallurgist determined that approximately 50 percent of the individual wires comprising the cable contained fatigue cracking.