Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 757-200, 757-200PF, and 757-300 series airplanes. This proposed AD would require, for certain airplanes, measuring the electrical bond resistance at certain stations and doing any applicable repair; installing support brackets for the hot short protector and new support clamps for the wire bundles; installing the equipment of the hot short protector; and modifying an existing wire bundle and installing a new wire bundle. This proposed AD would also require, for certain other airplanes, measuring the electrical bond resistance at certain stations, measuring the electrical bonding resistance between the hot short protector and rear spar web, and doing any applicable repair. This proposed AD also would require revising the Airworthiness Limitations section of the Instructions for Continued Airworthiness. This proposed AD results from fuel system reviews conducted by the manufacturer. We are proposingthis AD to prevent the center fuel tank densitometer from overheating and becoming a potential ignition source inside the fuel tank, which, in combination with flammable fuel vapors, could result in a center fuel tank explosion and consequent loss of the airplane.