AD FAA-2013-0421

We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 737-300, -400, and -500 series airplanes. This AD was prompted by fuel system reviews conducted by the manufacturer. This AD requires, depending on airplane configuration, replacing fuel pump power control relays with new relays having a ground fault interrupter (GFI) feature, installing ground studs and a bonding jumper, doing certain bonding resistance measurements, and changing the GFI relay position. This AD also requires revising the maintenance program to incorporate certain airworthiness limitations. We are issuing this AD to prevent damage to the fuel pumps caused by electrical arcing that could introduce an ignition source in the fuel tank, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.