Incident
A pilot reported that during takeoff and climb through approximately 800 feet, a loud snap was heard accompanied by immediate severe lateral vibrations. An emergency was declared and the pilot landed without further incident.
Investigation Findings
Examination of the helicopter revealed that the inboard trailing ear of the main rotor sleeve/spindle assembly, part number 330A31-002607, for the blue blade had failed. The fracture surface exhibited evidence of fatigue over most of its area, with fretting corrosion found at the origin of the fatigue. Additionally, an area of fretting corrosion was present on the trailing side flange of the hinge pin, on a surface clamped by the torque of the hinge pin nut.
Maintenance records showed that Aerospatiale Service Bulletin 01.35 had been complied with on March 30, 1982, and the hinge pin had been replaced on April 10, 1982, approximately 100 flight hours before the failure.
A spot check of the maintenance facility disclosed that two of three torque wrenches were overdue for calibration. The third wrench, when set for 120 inch-pounds, actually delivered only 54 inch-pounds.