NEW : FAA grounded all U.S. aircraft over battery safety concern . Boeing : ` ` We will be taking every necessary action '' After Japan grounded the aircraft , experts worry most about Dreamliner 's lithium ion batteries .
NEW : FAA grounds all U.S. Dreamliners over battery fire concern . Boeing : `` We will be taking every necessary step '' After Japan grounded the 787 , experts worry most about Dreamliner 's lithium ion batteries .