Airworthiness Directives; The Boeing Company Airplanes

We propose to supersede an existing airworthiness directive (AD) that applies to certain Model 737-300, -400, and -500 series airplanes. The existing AD currently requires repetitive external detailed inspections or non-destructive inspections to detect cracks in the fuselage skin along the chem-mill steps at stringers S-1 and S-2R, between station (STA) 400 and STA 460, and repair if necessary. Since we issued that AD, we have received reports of additional crack findings of the fuselage skin at the chem-mill steps. This proposed AD would add inspections for cracking in additional fuselage skin locations, and repair if necessary. This proposed AD would also reduce the inspection thresholds and repetitive intervals for certain airplanes. We are proposing this AD to detect and correct fatigue cracking of the fuselage skin panels at the chem-mill steps, which could result in sudden fracture and failure of the fuselage skin panels, and consequent rapid decompression of the airplane.