Airworthiness Directives; Boeing Model 747-400 Series Airplanes Equipped With General Electric CF6-80C2 Series Engines

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747-400 series airplanes, that currently requires various inspections and functional tests to detect discrepancies of the thrust reverser control and indication system, and correction of any discrepancy found. This amendment adds an appendix and revises certain actions in the existing AD. This amendment is prompted by a report indicating that completion of the cone brake test of the center drive unit is ineffective for certain airplanes. The actions specified in this AD are intended to ensure the integrity of the fail safe features of the thrust reverser system by preventing possible failure modes in the thrust reverser control system that can result in inadvertent deployment of a thrust reverser during flight.