Airworthiness Directives; McDonnell Douglas Model DC-9-14, DC-9-15, and DC-9-15F Airplanes; and Model DC-9-20, DC-9-30, DC-9-40, and DC-9-50 Series Airplanes

We are adopting a new airworthiness directive (AD) for certain McDonnell Douglas airplanes listed above. This AD requires installing a dam assembly for the container of the fuel boost pump of the center tank located in the right main tank, and doing the related investigative actions, and corrective actions if necessary. This AD results from fuel system reviews conducted by the manufacturer. We are issuing this AD to prevent the center tank fuel boost pump from operating in a fuel vapor zone and becoming a potential ignition source in the right main tank, potentially resulting in a fuel tank explosion and consequent loss of the airplane.