Summary
We propose to supersede Airworthiness Directive (AD) 2009-21- 01, which applies to certain Boeing Model 737-300 and 737-400 series airplanes. AD 2009-21-01 currently requires repetitive inspections to detect cracking of the aft fuselage skin, and related investigative and corrective actions if necessary. Since we issued AD 2009-21-01, an evaluation by the design approval holder (DAH) indicates that the aft fuselage skin is subject to widespread fatigue damage (WFD). This proposed AD would add new aft fuselage skin inspections for cracking, inspections to detect missing or loose fasteners and any disbonding or cracking of bonded doublers, permanent repairs of time-limited repairs, related investigative and corrective actions if necessary, and skin panel replacement. The proposed AD also removes Model 737-400 series airplanes from the applicability. We are proposing this AD to detect and correct cracking in the aft fuselage skin along the longitudinal edges of the bonded skin doubler, which could result in possible rapid decompression and reduced structural integrity of the airplane.