The Federal Aviation Administration on Friday issued a directive mandating "a repetitive maintenance task" for that model of airlines due to issues with its power supply. Specifically, the FAA explained testing revealed that 787s could lose all AC electrical power after being continuously powered for 248 days, a problem that -- if left unchecked -- would leave an aircrew unable to control the plane.
http://www.cnn.com/2015/05/02/us/boeing-787-dreamliner-faa-directive/index.html
http://www.cnn.com/2015/05/02/us/boeing-787-dreamliner-faa-directive/index.html