Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes. This proposal would require 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 proposal also would require 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.