Summary
We propose to supersede Airworthiness Directive (AD) 2012-12- 04, which applies to certain The Boeing Company Model 737-300, -400, and -500 series airplanes. AD 2012-12-04 currently requires 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. Since we issued AD 2012-12-04, we have determined that, for certain airplanes, the skin pockets adjacent to the Air Traffic Control (ATC) antenna are susceptible to widespread fatigue damage. This proposed AD would require a preventive modification of the fuselage skin at crown stringers S-1 and S-2R. This proposed AD would reduce 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.