Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 737-600, -700, -800, and -900 series airplanes. This proposed AD would require installation of hot short protector (HSP) support brackets and equipment for the fuel quantity indicating system (FQIS) fuel densitometer and other specified actions as applicable. This proposed AD would also require a revision to the Airworthiness Limitations (AWLs) section of the Instructions for Continued Airworthiness to incorporate AWL No. 28-AWL-07. This proposed AD results from fuel system reviews conducted by the manufacturer. We are proposing this AD to prevent the center tank fuel densitometer from overheating and becoming a potential ignition source inside the center fuel tank, which, in combination with flammable fuel vapors, could result in a center fuel tank explosion and consequent loss of the airplane.