AD FAA-2017-0771

We are superseding Airworthiness Directive (AD) 2015-09-07, which applied to all The Boeing Company Model 787 airplanes. AD 2015- 09-07 required a repetitive maintenance task for electrical power deactivation. This AD requires installing new software for the generator control unit (GCU). This AD also removes certain airplanes from the applicability. This AD was prompted by the determination that a Model 787 airplane that has been powered continuously for 248 days can lose all alternating current (AC) electrical power due to the GCUs simultaneously going into failsafe mode. We are issuing this AD to address the unsafe condition on these products.