Airworthiness Directives; Siam Hiller Holdings, Inc. Model UH-12, UH-12A, UH-12B, UH-12C, UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters

This amendment adopts a new airworthiness directive (AD), for Siam Hiller Holdings, Inc. (Hiller), formerly Rogerson Hiller Corporation, Model UH-12, UH-12A, UH-12B, UH-12C, UH-12D, UH-12E, UH- 12E-L, UH-12L, and UH-12L4 helicopters, that requires replacing all undrilled-shank bolts at pivoting joints in the control system linkage with drilled-shank bolts and installing castellated nuts and cotter pins. This amendment is prompted by an accident caused by separation of the control system linkage of a Model UH-12E helicopter. The actions specified by this AD are intended to prevent separation of the control system attachments at pivoting points and subsequent loss of control of the helicopter.