Airworthiness Directives; The Boeing Company Model 737-600, -700, -700C, -800, and -900 Series Airplanes

요약

We propose to supersede an existing airworthiness directive (AD) that applies to the products listed above. The existing AD currently requires replacement of the power control relays in the P91 and P92 power distribution panels for the fuel boost and override pumps with new, improved relays having a ground fault interrupter (GFI) feature, or installation and maintenance of universal fault interrupters (UFIs) using a certain supplemental type certificate. Since we issued that AD, we have determined that we need to clarify which relays may be replaced by installation of UFIs. This proposed AD would continue to require the actions of the existing AD and also specify which relays may be replaced by GFIs or UFIs. We are proposing this AD to prevent pump housing burn-through due to electrical arcing, which could create a potential ignition source inside a fuel tank. This condition, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.