Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes

We are adopting a new airworthiness directive (AD) for certain Boeing Model 737-300, -400, and -500 series airplanes. This AD requires repetitive inspections for cracking of the body buttock line (BBL) 0.07 floor beam between body station (BS) 651 and BS 676 and between BS 698 and BS 717, and related investigative and corrective actions if necessary. This AD also provides an optional terminating action for the repetitive inspections. This AD results from reports of cracking in the BBL 0.07 floor beam. We are issuing this AD to prevent failure of the main deck floor beams at certain body stations due to fatigue cracking, which could result in rapid decompression of the airplane.