Airworthiness Directives; Textron Lycoming AEIO-540, IO-540, LTIO-540, O-540, and TIO-540 Series Reciprocating Engines

This amendment supersedes an emergency airworthiness directive (AD) that was sent previously to all known U.S. owners and operators of Textron Lycoming (T/L) AEIO-540, IO-540, LTIO-540, O-540, and TIO-540 series reciprocating engines. That action requires replacing certain zinc-plated crankshaft gear retaining bolts. This action still requires replacing certain zinc-plated crankshaft gear retaining bolts, but expands the population of affected engines. This amendment is prompted by two recent failures of zinc-plated crankshaft gear retaining bolts, and a reassessment of the extent to which the suspect bolts may still be present in the field. The actions specified by this AD are intended to prevent loss of all engine power and possible forced landing.