Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-400 and 747-400D series airplanes. This proposal would require a detailed inspection of the fire extinguishing system tube and clamp for correct installation or a repetitive pressure test of the fire extinguishing system tube for leakage, and corrective action, if necessary. This action is necessary to prevent a chafed hole in the fire extinguishing system tube of the aft cargo compartment, which could result in a lack of fire extinguishing agent and consequent uncontained fire in the aft cargo compartment. This action is intended to address the identified unsafe condition.