Incident Description
During the final approach phase, a tail rotor control cable on an Enstrom F-28C helicopter broke, leading to an abrupt left yaw. The flight instructor reported the loss of directional control and transitioned to a shallow approach, performing a run-on landing that resulted in no additional damage to the aircraft.
Post-Incident Inspection
A subsequent inspection found that the cable connecting the right anti-torque pedal to the tail rotor assembly had failed at a pulley located in the tail boom, immediately forward of bulkhead 5. The opposite cable, connecting the left anti-torque pedal, exhibited signs of wear at the same location. Both cable assemblies were removed and replaced.
Maintenance and Design History
The manufacturer's inspection procedures require review of tail rotor cables for wear and proper tension every 100 flight hours, with replacement based on cable condition. Following this incident, the operator indicated plans to replace the tail rotor control cables every 300 to 400 hours regardless of condition.
The helicopter was originally certified with a fairlead configuration where the cables pass through the aft bulkhead. A production design change later introduced a pulley configuration to address cable wear issues at the fairleads. The incident aircraft was equipped with this pulley configuration. However, no logbook entry or FAA Form 337 (major alteration record) documenting the retrofit was found.
Service Bulletin and Industry Reports
The manufacturer released a service bulletin requiring operators of Enstrom F-28F, 280F, and 280FX models (produced with the pulley configuration) to inspect for accelerated cable wear. Because the incident helicopter was an F-28C, the bulletin was not applicable and thus not performed. Subsequently, Enstrom reissued the service bulletin to include earlier models that had been modified with pulleys. Additionally, several FAA Service Difficulty Reports filed by mechanics noted cable wear requiring replacement at 300- to 400-hour intervals.