The FAA has issued an airworthiness directive for the 787:
SUMMARY: We are adopting a new airworthiness directive (AD) for all The Boeing Company Model 787 airplanes. This AD requires a repetitive maintenance task for electrical power deactivation on Model 787 airplanes. 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 generator control units (GCUs) simultaneously going into failsafe mode. This condition is caused by a software counter internal to the GCUs that will overflow after 248 days of continuous power. We are issuing this AD to prevent loss of all AC electrical power, which could result in loss of control of the airplane.
I'm curious: Are there any circumstances under which a 787 would remain powered continuously for 248 days?
[Edited to add a follow-on question:]
Boeing has said "If there is a definitive record of a powercycle within the last 120 days, no operator action is immediately required." Does that happen? 120 days?
What is the longest period a passenger aircraft might conceivably be continuously powered on?