Airworthiness Directives; Boeing Model 747 Airplanes

The FAA is superseding an existing airworthiness directive (AD), which applies to certain Boeing Model 747 series airplanes. That AD requires a one-time inspection for discrepancies of the potable water and drain lines in the cargo compartments, and corrective action if necessary. This new AD requires that the inspection be repetitively performed using new service information, until terminating action is done. This AD also removes certain airplanes from the applicability. This AD results from a report of a fire in the aft cargo compartment started by a potable water line heater tape. We are issuing this AD to prevent overheating of the heater tape on potable water fill and drain lines, which could ignite accumulated debris or contaminants on or near the potable water fill and drain lines, resulting in a fire in the airplane.