Airworthiness Directives; Hiller Aircraft Corporation Model UH- 12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters

This amendment supersedes an existing airworthiness directive (AD), applicable to Hiller Aircraft Corporation Model UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E helicopters, that currently requires a dye penetrant inspection of the head of the main rotor outboard tension- torsion (T-T) bar pin for cracks; a visual inspection of the outboard T-T bar pin for proper alignment and an adjustment, if necessary; and, installation of shims at the inboard end of the drag strut. This amendment requires the same actions required by the existing AD, but allows a magnetic particle inspection of the T-T bar pin as an alternative to the currently required dye penetrant inspection, and requires reporting the results of the inspections only if cracks are found, rather than reporting all results of inspections as required by the existing AD. This amendment is prompted by an FAA analysis of a comment to the existing AD, and the fact that no cracks have been reported since the issuance of the existing AD. The actions specified by this AD are intended to prevent cracks in the head area of the outboard T-T bar pin, which could result in loss of in-plane stability of the main rotor blade and subsequent loss of control of the helicopter.