Airworthiness Directives; Boeing Model 707 Airplanes and Model 720 and 720B Series Airplanes

The FAA is adopting a new airworthiness directive (AD) for all Boeing Model 707 airplanes and Model 720 and 720B series airplanes. This AD requires accomplishing an airplane survey to define the configuration of certain system installations, and repair of any discrepancy found. This AD also requires modifying the fuel system by installing lightning protection for the fuel quantity indication system (FQIS), ground fault relays for the fuel boost pumps, and additional power relays for the center tank fuel pumps and uncommanded on- indication lights at the flight engineer's panel. This AD results from fuel system reviews conducted by the manufacturer. We are issuing this AD to prevent certain failures of the fuel pumps or FQIS, which could result in a potential ignition source inside the fuel tank, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.