Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment corrects and clarifies an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that currently 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 existing AD also 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 corrects an inadvertent omission to reference a specific section of the appropriate service information, and clarifies certain other requirements. This amendment is prompted by a comment received subsequent to issuance of the existing final rule, requesting clarification of certain requirements of the existing AD. The actions specified in this AD are intended to prevent ignition sources and consequent fire/explosion in the center fuel tank.