Airworthiness Directives; The Boeing Company Model DC-9-14, DC-9-15, and DC-9-15F Airplanes; and DC-9-20, DC-9-30, DC-9-40, and DC-9-50 Series Airplanes

We are adopting a new airworthiness directive (AD) for the products listed above. This AD requires installing new in-line fuses for the fuel level float switch and new in-line fuses for the pressure switch, as applicable, and changing the wiring. The proposed actions would affect the left and right wing forward spars, center wing forward spar, forward auxiliary fuel tank, and aft auxiliary fuel tank, as applicable. This AD was prompted by fuel system reviews conducted by the manufacturer. We are issuing this AD to prevent the potential of ignition sources inside fuel tanks, which, in combination with flammable fuel vapors, could result in fuel tank explosions and consequent loss of the airplane.