The electrical systems on Boeing 787s need to be shut down and restarted before they reach 248 days of continuous power, the FAA said on Friday, to prevent a “loss of all AC electrical power, which could result in loss of control of the airplane.” The airworthiness directive was issued “straight to final rule,” without a preliminary notice, and is effective immediately. The FAA said it was informed about the problem by Boeing, and the manufacturer is working on a software upgrade that will address the issue. “Once this software is developed, approved, and available, we might consider additional rulemaking,” the FAA said.
According to the AD, the software internal to the generator control units (GCUs) will overflow after 248 days, causing that GCU to go into failsafe mode. “If the four main GCUs (associated with the engine mounted generators) were powered up at the same time, after 248 days of continuous power, all four GCUs will go into failsafe mode at the same time, resulting in a loss of all AC electrical power regardless of flight phase,” the AD says. The reboot procedure can be completed with just one hour of work, the FAA said, and there is no other cost involved.
