What happened
On July 27, 2022, at approximately 1725 Alaska daylight time, a Cessna 207A, registration N6908M, was involved in an accident near Dilling and Dillingham, Alaska. The aircraft was operating as a Part 135 scheduled flight. During the approach to landing, the pilot discovered that the left rudder pedal was unresponsive. The pilot declared an emergency and completed the landing without further incident. There were no injuries to the pilot or the two passengers, but the aircraft sustained substantial damage.
The investigation
An inspection by a Federal Aviation Administration inspector found that a rudder cable had fractured, with visible rust at the break. The fracture occurred approximately 94 inches from the turnbuckle terminal end and 152 inches from the clevis attachment holes. While the bearings in both pulleys moved freely, the left pulley showed abrasion on its outer rim and orange deposits consistent with rust in the groove. Additionally, the cable contact pattern on the right pulley was offset from the groove centerline.
Maintenance records showed that the last flight control inspection occurred on November 23, 2021. A logbook entry from January 5, 2022, noted a stuck left-hand rudder pulley and corrosion on the left rudder cable near the aft baggage bulkhead; however, the mechanic's follow-up entry stated that no defects were found after further inspection.
Findings
Investigation revealed that the left rudder cable failed due to corrosion and severe wear at the left pulley. Most wires on the cable had worn down to a chisel-like point, leaving only a few strands in the core to fail via ductile overstress. The wear and corrosion were likely accelerated by sliding contact within the pulley groove. Evidence suggested the left pulley was contacting adjacent structure, which interfered with its rotation. Furthermore, an alignment issue was identified at the right pulley, as indicated by the offset cable contact pattern.