Airworthiness Directives; The Boeing Company Airplanes

We are superseding an existing airworthiness directive (AD) for certain The Boeing Company Model 737-300, -400, and -500 series airplanes. That 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. This new AD adds inspections for cracking in additional fuselage skin locations, and repair if necessary. This new AD also reduces the inspection thresholds and repetitive intervals for certain airplanes. This AD was prompted by reports of additional crack findings of the fuselage skin at the chem-mill steps. We are issuing 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.