Airworthiness Directives; The Boeing Company Model 737-300, -400, and -500 Series Airplanes

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We are superseding an existing airworthiness directive (AD) for certain Model 737-300, -400, and -500 series airplanes. That AD currently requires repetitive inspections for cracking of the 1.04-inch nominal diameter wire penetration hole, and applicable related investigative and corrective actions. This AD reduces the compliance times for those actions. This AD was prompted by reports of cracking in the frame, or in the frame and frame reinforcement, common to the 1.04- inch nominal diameter wire penetration hole intended for wire routing; and recent reports of multiple adjacent frame cracking found before the compliance time required by the existing AD. Such cracking could reduce the structural capability of the frames to sustain limit loads, and result in cracking in the fuselage skin and subsequent rapid depressurization of the airplane. We are issuing this AD to correct the unsafe condition on these products.