CHI04IA018 · Enstrom F-28C

The helicopter sustained minor damage when a tail rotor control cable broke while on final approach. The flight instructor stated that the helicopter abruptly yawed to the left. He reported that he transitioned to a shallow approach and executed a run-on landing without further damage to the helicopter. A post-incident inspection revealed that the cable connecting the right anti-torque pedal to the tail rotor assembly had failed. The failure point was located in the tail boom at the pulley installed immediately forward of bulkhead 5. The opposite cable, connecting the left anti-torque pedal to the tail rotor assembly, showed signs of wear at the same location. Both cable assemblies were removed and replaced. The manufacturer's inspection procedures required review of the tail rotor cables for wear and proper tension every 100 hours. Replacement was based on cable condition. Due to this incident, the operator has indicated that they plan to replace the tail rotor control cables every 300 - 400 hours regardless of condition. The helicopter was originally certified with a fairlead configuration at the point at which the tail rotor control cables pass through the aft bulkhead. A production design change subsequently revised this to a pulley configuration due to indications of cable wear at the fairleads. This pulley configuration was installed on the incident aircraft. A logbook entry or major alteration record (FAA form 337) denoting retrofit of the pulley configuration on the incident aircraft was not found. The manufacturer released a service bulletin requiring operators of F-28F, 280F and 280FX model Enstrom helicopters, produced and type certified with the pulley configuration, to inspect the tail rotor control cables for signs of accelerated wear. Since the incident helicopter was an F-28C, the inspection outlined in the service bulletin was not applicable and, therefore, was not performed. Enstrom has reissued the service bulletin in order to include earlier model helicopters which have been modified to include the pulleys. Several FAA Service Difficulty Reports related to wear of the tail rotor control cables have been filed by mechanics. Reports indicated replacement of cables at 300 - 400 hour intervals has been required due to wear.

Verbatim NTSB analysis and probable cause from the NTSB dataset