Incident Overview
During cruise flight, the pilot of the helicopter heard a loud bang and subsequently lost tailrotor authority. The pilot maneuvered the aircraft for landing and reduced airspeed in anticipation of touchdown. The helicopter began to rotate. At an altitude of approximately 30 to 50 feet above ground level, the pilot pulled the collective to cushion the landing. The helicopter then impacted the ground and rolled onto its side.
Maintenance History
The helicopter had received an annual inspection 11 months and 23.3 flight hours before the accident. During that inspection, the mechanic documented that Airworthiness Directive (AD) 76-18-01 had been complied with.
Examination Findings
Post-accident examination of the left aft cluster fitting revealed that the tailboom attaching point had separated, severing the tailrotor drive shaft. The fracture surfaces of the cluster fitting were relatively flat with smooth curving boundaries, which were described as features typical of fatigue. Most of the relatively rough area in the lower lug displayed curving arrest lines, features typical of low-cycle fatigue.
Airworthiness Directive and Inspections
AD 76-18-01 required that within 50 flight hours of the effective date, and thereafter at intervals not exceeding 50 flight hours (or until modifications were accomplished), the tailboom support strut aluminum end fittings be visually inspected for deformation or damage, and then checked for cracking using dye penetrant. If cracking or damage was identified, the affected structure would need replacement. The AD mandated that the dye penetrant inspection be conducted in accordance with Service Information Notice N-82.3. That notice additionally required a daily visual inspection, which the pilot stated he performed prior to the flight.