Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes. The amendment requires a one-time inspection to detect discrepancies of the center fuel tank wiring and components, and corrective action, if necessary; and a one-time electrical bonding test of the center fuel tank components, and rework, if necessary. For certain airplanes, the amendment requires a one-time insulation resistance test and a one-time inspection to detect discrepancies of the wiring and components of the fuel quantity indication system (FQIS), and corrective actions, if necessary; replacement of certain FQIS probes with certain newer probes; a system adjustment and system operational test; and modification (installation of a flame arrestor) of the inlet line of the scavenge pump of the center fuel tank. This amendment is prompted by design review and testing results obtained in support of an accident investigation. The actions specified by this AD are intended to prevent ignition sources and consequent fire/explosion in the center fuel tank.