Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 747 series airplanes. This proposed AD would require replacing the power control relays for the main tank fuel boost pumps and jettison pumps, and the center tank scavenge pump, as applicable, with new relays having a ground fault interrupt (GFI) feature. The proposed AD also would require revising the maintenance program to incorporate Airworthiness Limitations (AWLs) No. 28-AWL-23 (for Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747- 200F, 747-300, 747SP, and 747SR series airplanes), and Nos. 28-AWL-28 and 28-AWL-29 (for Model 747-400, 747-400D, and 747-400F series airplanes). This proposed AD results from fuel system reviews conducted by the manufacturer. We are proposing 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.