Airworthiness Directives; Various Restricted Category Helicopters

We are adopting a new airworthiness directive (AD) for various restricted category Model HH-1K, TH-1F, TH-1L, UH-1A, UH-1B, UH-1E, UH- 1F, UH-1H, UH-1L, and UH-1P helicopters with certain main rotor hub inboard strap fittings (fittings) installed. This AD requires a magnetic particle inspection (MPI) of the fittings for a crack, and if there is a crack, replacing the fitting with an airworthy fitting. This AD is prompted by reports of cracked fittings on Bell model helicopters and the determination that these same part-numbered fittings may be installed on various restricted category helicopters. These actions are intended to detect a crack in a fitting, which may lead to failure of a fitting, loss of a main rotor blade, and subsequent loss of helicopter control.