TOKYO (AP) -- U.S. safety officials and Boeing inspectors joined a Japanese investigation Friday into the 787 jet at the center of a worldwide grounding of the technologically advanced aircraft.
Japanese TV footage showed the American investigators -- one each from the Federal Aviation Administration and the National Transportation Safety Board and two from Boeing Co. -- inspecting the All Nippon Airways jet on the tarmac at Takamatsu airport in western Japan.
The investigation is being led by the Japan Transport Safety Board.
The pilot of the ANA plane made an emergency landing Wednesday morning after he smelled something burning and received a cockpit warning of battery problems. All passengers evacuated the plane on emergency slides.
The American inspectors were expected to examine the battery later Friday, said Mamoru Takahashi, a JTSB official. Photos of the battery provided by JSTB show a blackened mass of wires and other components within a distorted blue casing.
In the wake of the incident, nearly all 50 of the 787s in use around the world have been grounded. Aviation authorities in Japan have directed ANA, which owns 17 of the planes, and Japan Airlines, with seven, not to fly the jets until questions over their safety have been resolved.
The 787, known as the Dreamliner, is Boeing's newest jet, and the company is counting heavily on its success. Since its launch after delays of more than three years, the plane has been plagued by a series of problems including a battery fire and fuel leaks.
An initial inspection by Japanese officials of the 787 in Takamatsu found that a flammable battery fluid known as electrolyte had leaked from the plane's main lithium-ion battery beneath the cockpit. It also found burn marks around the battery.
The 787 relies more than any other modern airliner on electrical signals to help power nearly everything the plane does. It's also the first Boeing plane to use rechargeable lithium-ion batteries for its main electrical system.
GS Yuasa Corp., the maker of the lithium-ion batteries used in the 787s, said it was helping with the investigation but that the cause of the problem was unclear.
The FAA has required U.S. carriers to stop flying 787s until the batteries are demonstrated to be safe. United Airlines has six of the jets and is the only U.S. carrier flying the model.
Aviation authorities in other countries usually follow the lead of the country where the manufacturer is based.