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

This amendment adopts a new airworthiness directive (AD) that is applicable to Hiller Aircraft Corporation (Hiller) Model UH-12A, UH- 12B, UH- [[Page 30185]] 12C, UH-12D, and UH-12E helicopters. This action 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 is prompted by two accidents involving failure of the outboard T-T bar pin on Hiller UH-12E helicopters. 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.