NTSB Factual Report

On October 22, 2003, at 1400 eastern daylight time, an Enstrom F-28C helicopter, N77HX, piloted by a flight instructor and dual student, sustained minor damage when a tail rotor control cable broke while on final approach to the Dupont-Lapeer Airport (D95), Lapeer, Michigan. The local instructional flight was being conducted under 14 CFR Part 91 and was not on a flight plan. Visual meteorological conditions prevailed at the time of the incident. Neither the instructor nor the dual student reported any injuries.

The flight instructor reported that on short final, about 200 feet above ground level, the helicopter unexpectedly yawed to the left. He also reported a "jarring" of the aircraft. He stated he lowered the collective and applied right pedal, but this did not affect the yawing tendency. He noted: "I applied power and realized I had some left pedal and no right pedal" control authority. The instructor reported that he transitioned to a shallow approach and executed a run-on landing. He recalled: " We touched down with approximately 30 [degrees] left yaw. [The] aircraft slid approximately 5 [feet] and came to rest with no damage."

A post-incident inspection revealed that the cable connecting the right anti-torque pedal to the tail rotor assembly had failed (P/N 28-16351-1). The failure occurred at the pulley installed immediately forward of bulkhead 5, located in the tail boom of the helicopter. The opposite cable, connecting the left anti-torque pedal to the tail rotor assembly, showed signs of wear at the corresponding location. Both cable assemblies were removed and replaced. The pulleys were intact and free to rotate. They showed no signs of unusual wear.

The incident aircraft was a 1979 model year F-28C Enstrom helicopter (serial number 4702). An annual inspection was completed on September 9, 2003, at a total airframe time of 3,471.1 hours. At the time of the incident, the aircraft had accumulated an additional 66.4 hours, for a total airframe time of 3,537.5 hours. The operator reported the time in-service of the failed cable as 895 hours.

According to the manufacturer, 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 incident helicopter was originally certified with a fairlead configuration at the point at which the tail rotor control cables pass through the aft bulkhead. According to the manufacturer, this design was revised to a pulley configuration due to indications of accelerated cable wear at the fairleads. This pulley configuration was installed on the incident aircraft as a field modification, reportedly in December 2000.

Review of the airframe logbook of the incident aircraft did not reveal any entry denoting installation of pulleys at the aft bulkhead. No major alteration data (FAA form 337) related to the tail rotor cable and installed pulley configuration were found with the helicopter's maintenance or airworthiness records.

A review of Federal Aviation Administration (FAA) records revealed no applicable Supplemental Type Certificates on file authorizing retrofit to the pulley configuration.

The helicopter manufacturer released Service Directive Bulletin No. 0093 on March 6, 2000, requiring operators of F-28F, 280F and 280FX model Enstrom helicopters to inspect the tail rotor control cables. This inspection was required within 10 flight hours for aircraft with more than 200 hours total time, and at the next 100 hour/annual inspection for aircraft with less than 200 hours total time.

Since the incident helicopter was an F-28C, the inspection outlined in the original service bulletin was not applicable and, therefore, was not performed. Enstrom reissued the service bulletin on December 9, 2003, in order to include earlier model helicopters which have been modified to incorporate the pulley configuration.

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.

FAA regulations define a major airframe alteration as: "Alterations of the following parts and alterations of the following types, when not listed in the aircraft specifications issued by the FAA, are airframe major alterations: . . . (v) Control system." The regulations also require that FAA Form 337, Major Repair and Alteration, be completed and submitted to the aircraft owner and the local FAA Flight Standards District Office within 48 hours of the aircraft's return to service.

NTSB Probable Cause

Complete failure of the right anti-torque cable while on final approach for landing. A factor was the diminished tail rotor control resulting from the broken cable.