AD FAA-2011-1255

We are superseding two existing airworthiness directives (ADs) for certain 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. This new AD requires that the inspection for cracking under the stop fittings be done on additional airplanes; extends the repetitive interval for certain airplanes; adds a one-time inspection to detect missing fasteners; and updates or adds certain inspection and repair instructions. This new AD also requires, for certain airplanes, repetitive inspections of the cargo barrier net fitting for cracking, and repair if necessary. This new AD also adds, for certain airplanes, repetitive inspections for cracking of the stringer S-15L aft intercostal, and repair if necessary. This AD was prompted by 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. We are issuing this AD to detect and correct fatigue cracking of the intercostals on the forward and aft sides of the forward entry door cutout, which could result in loss of the forward entry door and rapid decompression of the airplane.