Aviation safety and battery experts say it is likely that fires on two Boeing 787 Dreamliner planes were caused by overcharging lithium ion batteries.
An All Nippon Airways Dreamliner was forced to make an emergency landing in Japan Wednesday after its pilots smelled something burning in the cockpit.
An investigator said Friday that the battery's burned insides indicate it operated at a voltage above its design limit.
A similar problem was found on a battery in a Japan Airlines Boeing 787 parked in Boston's Logan International Airport, earlier this month.
The Federal Aviation Administration issued an emergency order Wednesday grounding all the Boeing 787 planes operated by U.S. carriers. Japan, India, Europe and Qatar also grounded their Dreamliners until the problem is solved.
U.S. aviation experts arrived in Japan Friday to help determine what caused a battery to overheat and leak on the All Nippon Airways Dreamliner jet Wednesday.