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

Riepilogo

We are superseding an existing airworthiness directive (AD) for the products listed above. That 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. This new AD continues to require the actions of the existing AD and also specifies which relays may be replaced by GFIs or UFIs. This AD was prompted by a need to clarify which relays may be replaced by installation of UFIs. We are issuing 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.