Airworthiness Directives; Boeing Model 737-200, -200C, -300, -400, and -500 Series Airplanes

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing airplane models, that currently requires 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. This amendment requires 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 terminates the existing requirements. For certain airplanes, this amendment also requires replacing certain existing sections of the electrical conduit in the center fuel tank with new conduit. This amendment also adds one additional airplane model to the applicability and removes another. The actions specified by this AD are intended 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. This action is intended to address the identified unsafe condition.