The FAA issued a notice of proposed rulemaking to revise an existing airworthiness directive for the AgustaWestland AW139 requiring inspection of the fuselage frame to detect fatigue cracks that could lead to structural failure and subsequent loss of control. Since the AD was issued, AgustaWestland developed a frame reinforcement modification that supports extending the interval for inspecting the fuselage frame for a fatigue crack. The proposed AD requires inspecting the fuselage frame but would reduce the applicability from the existing AD to exclude helicopters modified by the optional frame-reinforcement modification.