Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 737-300, -400, and -500 series airplanes. This proposed AD would require 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 proposed AD results from fuel system reviews conducted by the manufacturer. We are proposing 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.