Airworthiness Directives; Various Transport Category Airplanes

We are superseding an existing airworthiness directive (AD) for certain transport category airplanes. That AD currently requires 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. This new AD requires installing a supplemental oxygen system in affected lavatories, which terminates the requirements of the existing AD. This AD was prompted by reports that the current design of the oxygen generators presents a hazard that could jeopardize flight safety. 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.