Airworthiness Directives; The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 Series Airplanes

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We propose to supersede two existing airworthiness directives (AD) that apply to Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. The first existing AD currently requires, for certain airplanes, repetitive inspections of the Station (STA) 348.2 frame to detect cracking under the stop fittings and intercostal flanges at stringers S-14L, S-15L, and S-16L, and corrective action if necessary. The second existing AD currently requires repetitive inspections to detect cracking of the intercostal webs, attachment clips, and stringer splice channels, and corrective action if necessary. Since we issued those ADs, we have received reports of cracking of the STA 348.2 frame above the two outboard fasteners attaching the frame inner chord and door stop fittings, and in the outboard chord at stringer S-16L. We have also received reports of missing fasteners in the STA 348.2 frame inner chord. This proposed AD would require additional airplanes to do the inspection for cracking under the stop fittings; extend the repetitive interval for certain airplanes; add a one-time inspection to detect missing fasteners; and update or add certain inspection and repair instructions. This pr