Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires a one-time inspection for chafing between the hose for the passenger oxygen system (hereinafter called the "oxygen hose") and adjacent electrical wire bundles at certain passenger service units, and corrective actions, if necessary. This AD also requires rerouting or reorienting the oxygen hose to ensure sufficient clearance between the hose and electrical wire bundles. This action is necessary to prevent chafing between the oxygen hose and adjacent electrical wire bundles, which could result in arcing of a chafed electrical wire bundle and consequent burn-through of the oxygen hose. If this occurs when the oxygen system is pressurized, such arcing could represent a potential ignition source in an oxygen-enriched environment. This action is intended to address the identified unsafe condition.