Summary
This document revises an earlier proposed airworthiness directive (AD), applicable to certain Boeing airplane models, that would have superseded an existing AD currently requiring either inspections for discrepancies of the fueling float switch wiring in the center fuel tank and follow-on actions, or deactivation of the float switch. The proposed AD would have removed the option to deactivate the float switch and would have required repetitive inspections for discrepancies of the float switch wiring and various other actions. This new action would require replacing the float switches in the center and wing fuel tanks with new, improved parts, installing a conduit liner system in the center fuel tank, and replacing conduit assemblies in the wing fuel tanks with new parts, which would terminate the existing requirements. For certain airplanes, this new action also would require replacing certain existing sections of the electrical conduit in the center fuel tank with new conduit. This new action also would add one additional airplane model to the applicability and remove another. These actions are necessary to prevent contamination of the fueling float switch by moisture or fuel, and chafing of the float switch wiring against the fuel tank conduit, which could present an ignition source inside the fuel tank that could cause a fire or explosion. These actions are intended to address the identified unsafe condition.