Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes Equipped With a Digital Transient Suppression Device (DTSD) Installed in Accordance With Supplemental Type Certificate (STC) ST00127BO

We are adopting a new airworthiness directive (AD) for certain Boeing Model 737-300, -400, and -500 series airplanes. This AD requires revising the maintenance program to include new fuel system limitations for airplanes modified in accordance with STC ST00127BO. This AD also requires inspections and checks of the DTSDs and corrective actions, if necessary. This AD results from fuel system reviews conducted by the manufacturer. We are issuing this AD to prevent a potential of ignition sources inside fuel tanks, which, in combination with flammable fuel vapors, could result in a fuel tank fire or explosion and consequent loss of the airplane.