Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 727 airplanes. This proposed AD was prompted by fuel system reviews conducted by the manufacturer. This proposed AD would require modifying the fuel quantity indicating system (FQIS) to prevent development of an ignition source inside the body-mounted auxiliary fuel tanks due to electrical fault conditions. As an alternative to the modification, this proposed AD would allow deactivating the body-mounted auxiliary fuel tanks. We are proposing this AD to prevent ignition sources inside the body-mounted auxiliary fuel tanks, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.