Airworthiness Directives; The Boeing Company Airplanes

We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. This proposed AD was prompted by reports that frame web and frame integral inboard chord cracking is occurring on multiple airplanes in multiple locations below the passenger floor. This proposed AD would require repetitive detailed, general visual, and high frequency eddy current (HFEC) inspections of the section 43 lower lobe frames at certain stations; an inspection to determine if certain repairs are installed; and applicable on-condition actions. We are proposing this AD to address the unsafe condition on these products.