Dillingham, AK, USA
N6908M
CESSNA 207
The pilot reported that, during approach to landing, he became aware that the left rudder pedal was not responsive. He declared an emergency and landed uneventfully. Examination revealed that the left rudder cable fractured due to corrosion and severe cable wear at the left pulley location. Nearly all wires on the cable were worn to a chisel-like point, leaving a small number of wires in the core strand to fracture in ductile overstress during final separation. The cable corrosion and wear were likely accelerated due to sliding contact with the left pulley. Issues with the rudder control system installation were evident on both pulleys. Rubbing damage on the face of the left pulley indicated that the pulley was contacting adjacent structure at the outer diameter. This contact likely interfered with pulley rotation, leading to the accelerated corrosion and wear of the control cable from sliding contact within the pulley groove. Although no rubbing damage was observed on the right pulley, the cable contact pattern was offset from the groove centerline, indicating an alignment problem in the rudder control system at the right pulley. Review of the maintenance logs revealed that the last inspection of the flight controls was completed about 8 months before the accident, and an entry about 3 months later noted a stuck pulley and corrosion of the left rudder cable. The maintenance response to the entry stated, “upon further inspection, determined cable not corroded. . . No defects.” Given the findings of the postaccident examination, it is likely that the accident would have been prevented had maintenance personnel taken more proactive action at that time.
On July 27, 2022, about 1725 Alaska daylight time, a Cessna 207A, N6908M, was substantially damaged when it was involved in an accident near Dillingham, Alaska. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 scheduled flight. The pilot reported that, during approach to landing he became aware that the left rudder pedal was not responsive. The pilot declared an emergency and landed uneventfully. Examination of the airplane by a Federal Aviation Administration inspector revealed that one of the rudder cables had fractured, and rust was visible at the fracture location. Because the failure of the rudder cable adversely affected the performance and flight characteristics of the airplane and required replacement of the cable, the damage to the airplane was substantial. Follow-up examination revealed that the rudder cable was fractured about 94 inches from the turnbuckle terminal end and 152 inches from the center of the attachment holes in the clevis at the other end. The bearings at the centers of the pulleys moved freely in both submitted pulleys; however, examination revealed abrasion of the outer rim of the left pulley and orange deposits consistent with rust in the groove for the left pulley in addition to rubbing around much of the circumference of the groove contact surface. Although no rubbing damage was observed on the right pulley, the cable contact pattern was offset from the groove centerline. The fractured ends of the cable were mostly worn to a tapered end with no discernable fracture features, consistent with ductile overstress fracture. Review of the maintenance logs revealed that the last inspection of the flight controls was completed on November 23, 2021, about 8 months before the accident, at an airplane total time of 40,516.8 hours. An entry on January 5, 2022, and airplane total time 40,536.6 hours, notated that “the left hand rudder stuck pulley at the aft baggage bulkhead” as well as “corrosion of the L/H rudder cable at aft baggage bulkhead.” The mechanic’s response to the entry stated, “upon further inspection, determined cable not corroded. . . No defects.” The airplane had accrued 40,885 total hours at the time of the accident.
Maintenance personnel’s failure to detect and correct improper rudder control system alignment, the resulting interference with the pulley’s rotation, and the accelerated corrosion and wear of the control cable, which ultimately led to its failure in flight.
Source: NTSB Aviation Accident Database
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