Airworthiness Directives; Sikorsky Aircraft Model S-76B Helicopters

This amendment supersedes an existing Airworthiness Directive (AD), applicable to Sikorsky Aircraft Model S-76B helicopters, that requires an inspection of the drive shaft for cracks or loose balance weights. This amendment also supersedes a Priority Letter AD that currently requires repetitive inspections for cracks in the driveshaft in helicopters with certain engine drive shaft assemblies (drive shafts) installed. This amendment is prompted by a report of a fatigue crack found in a drive shaft that was caused by fretting of a balance weight rivet washer. The actions specified by this AD are intended to prevent failure of the drive shaft, loss of power to the rotor system, and a subsequent forced landing of the helicopter.