Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, and -500 Series Airplanes

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 737-100, -200, -300, -400, and - 500 series airplanes. This action requires removal of the float switch and wiring and inspection of the float switch wiring in the center fuel tank to detect discrepancies, and either reinstallation of existing float switch and wiring, or replacement of the float switch and wiring with a new float switch and wiring. This action also requires installation of Teflon sleeving over the wiring of the float switch. In lieu of the above mentioned requirements, this AD requires deactivation of the float switch, accomplishment of specific fueling procedures, and installation of Caution signs. This amendment is prompted by a report indicating that chafing of the direct current (DC) powered float switch wiring insulation in the center fuel tank has occurred on several airplanes. The actions specified in this AD are intended to detect and correct such chafing and the resultant arcing from the wiring to the in-tank conduit, which could present an ignition source inside the fuel tank and consequent fire/explosion.