Airworthiness Directives; Airbus Model A300 B4-600, B4-600R, and F4-600R (Collectively Called A300-600) Series Airplanes; and Model A310 Series Airplanes; Equipped With Pratt & Whitney JT9D-7R4 or 4000 Series Engines

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Airbus Model A300-600 and A310 series airplanes, that currently requires deactivating both thrust reversers and revising the airplane flight manual (AFM) to ensure safe and appropriate performance during certain takeoff conditions. This amendment requires installing modifications that will add an independent third line of defense on the thrust reversers, which would enhance their redundancy and terminate the requirements of the existing AD. The actions specified by this AD are intended to prevent in-flight deployment of the thrust reversers, which could result in reduced controllability of the airplane. This action is intended to address the identified unsafe condition.