MORE BUMPS: There have been two emergencies in two weeks involving batteries on Boeing Co. 787s. Japan's two big airlines, which fly a combined 24 787s, grounded their 787 fleets on Wednesday for safety checks.

SPARKING CONCERN: The 787 relies on electricity more than other planes, so the problems with its power system go to the heart of the plane's design.

ON THE RADAR: U.S. and Japanese investigators are studying both incidents to figure out what went wrong. They haven't said how long that will take.