Airworthiness Directives; Learjet Model 45 Airplanes

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Learjet Model 45 airplanes. This action requires revising the airplane flight manual (AFM) to prohibit flight into known icing conditions; inspecting the anti-ice manifold assembly for missing material, and performing corrective actions if necessary; replacing the anti-ice manifold assembly with a new assembly, which terminates the AFM revision requirement; and revising the Learjet 45 maintenance program to incorporate additional inspections and maintenance practices for the anti-ice manifold assembly. This action is necessary to prevent metal fragments from breaking off the anti-ice manifold assembly due to fatigue, which could block a duct in the anti- ice system and result in an unannunciated loss of ice protection. This action is intended to address the identified unsafe condition.