AD FAA-2015-3628

We are superseding Airworthiness Directive (AD) 2012-12-04, for certain The Boeing Company Model 737-300, -400, and -500 series airplanes. AD 2012-12-04 required repetitive external detailed inspections and nondestructive 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 requires a preventive modification of the fuselage skin at crown stringers S-1 and S-2R. This new AD also reduces the inspection threshold for certain airplanes. This AD was prompted by a determination that, for certain airplanes, the skin pockets adjacent to the Air Traffic Control (ATC) antenna are susceptible to widespread fatigue damage. 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.