Airworthiness Directives; Various Transport Category Airplanes

We are revising Airworthiness Directive (AD) 2012-11-09 for certain transport category airplanes. AD 2012-11-09 required either activating all chemical oxygen generators in the lavatories until the generator oxygen supply is expended, or removing the oxygen generator(s); and, for each chemical oxygen generator, after the generator is expended (or removed), removing or restowing the oxygen masks and closing the mask dispenser door. AD 2012-11-09 also required installing a supplemental oxygen system in affected lavatories, which terminated the requirements of AD 2012-11-09. This AD clarifies a certain restriction by providing a broader method of compliance. This AD was prompted by the discovery that the requirement to change the instructions for continued airworthiness under certain conditions may impose an unnecessary burden on operators. We are issuing this AD to eliminate a hazard that could jeopardize flight safety, and to ensure that all lavatories have a supplemental oxygen supply.