Airworthiness Directives; The Boeing Company Airplanes

We are superseding an existing airworthiness directive (AD) for The Boeing Company Model 787-8 airplanes. That AD currently requires modification of the battery system, or other actions. This AD requires installing main and auxiliary power unit (APU) battery enclosures and environmental control system (ECS) ducts; and replacing the main battery, APU battery, and their respective battery chargers. This AD also requires revising the maintenance program to include an airworthiness limitation. This AD also revises the applicability by removing airplanes on which these changes have been incorporated in production prior to delivery. This AD was prompted by recent incidents involving lithium ion battery failures that resulted in release of flammable electrolytes, heat damage, and smoke on two Model 787-8 airplanes. We are issuing this AD to minimize the occurrence of battery cell failures and propagation of such failures to other cells and to contain any flammable electrolytes, heat, and smoke released during a battery thermal event in order to prevent damage to critical systems and structures and the potential for fire in the electronics equipment bays.