Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Airbus Model A330 and A340 series airplanes. This proposal would require a one-time inspection to determine the manufacturer's name, part number, and date code of certain circuit breakers; and replacement of any suspect circuit breaker with a new improved circuit breaker. This action is necessary to ensure that proper circuit breakers are installed for the fire extinguishing system or part of the supplemental oxygen supply. A defective circuit breaker, if not corrected, could trip without the cockpit indication light illuminating. If the flightcrew is unaware of this situation while operating the airplane, this latent failure in combination with other failures could present an immediate hazard to the airplane. This action is intended to address the identified unsafe condition.