Publication of the emergency AD comes in the wake of Lycoming mandatory service bulletin SB 632 released last month that outlines the procedures for completing the engine inspections. The FAA says 778 airplanes on the U.S. registry will be impacted by the AD, which carries an estimated total cost to U.S. engine owners of $1.1 million, or about $1,425 per engine, if no replacements are required.