WASHINGTON (AP) - FAA grounds Boeing 787 Dreamliner pending safety check of plane's lithium batteries .
The move comes after U.S. air safety investigators headed to Japan with representatives of Boeing.
They plan to join Japanese investigators in a probe of problems plaguing Boeing's new 787.
Japan's two biggest carriers, Japan Airlines and All Nippon Airways, have grounded all of their 787s for safety checks, after one was forced to make an emergency landing.
Battery fires and fuel leaks have been among the problems reported.