US and Japanese experts on Friday joined forces to investigate an ANA Dreamliner whose emergency landing has provoked the grounding of the world's entire 787 fleet and embroiled Boeing in crisis.
The risk of fire from overheating batteries has emerged as a major concern for Boeing's cutting-edge new planes since the incident on the domestic flight in Japan, prompting airlines to ground all 50 of the world's operational 787s.
The All Nippon Airways Dreamliner has remained on the tarmac at Takamatsu in southwest Japan since its pilots were forced into the dramatic landing on Wednesday because of a smoke alert apparently linked to a lithium-ion battery.
A team from the US National Transportation Safety Board, which includes members from the FAA and Boeing, has arrived in Takamatsu to take part in the Japanese investigation, a spokesman for the Japan Transport Safety Board said.
"We removed the battery yesterday and are today inspecting the plane and its components, alongside the US officials," said the spokesman, Mamoru Takahashi.
The batteries used for the Dreamliner's advanced electronics are made by Japan's GS Yuasa, one of many contractors in a complex global chain that led to three years of delays before Boeing delivered its first 787 to ANA in 2011.
Electrolyte leaks and burn marks were found on the battery's metal casing after Wednesday's emergency landing, ANA says. GS Yuasa -- while defending its reputation for quality -- has warned that the investigation could take weeks.
Japan Transport Safety Board investigator Hideyo Kosugi said one theory being considered was that there may have been insufficient protection offered by the batteries' surrounding electrical system, which would also come under scrutiny.
"I'm sure that too much current or too-high voltage has gone to the battery," Kosugi told reporters.
A prolonged grounding could seriously compound the crisis for Boeing, which had suffered a series of glitches over the week leading up to the ANA incident including another smoke alert on a Japan Airlines Dreamliner at Boston airport.
Hans Weber, an independent security and defence expert, said Boeing had been too optimistic about the benefits of its worldwide outsourcing strategy to build the 787.
"Boeing has admitted that it underestimated the level of management oversight and engineering support it needed to provide to its suppliers to make the highly distributed supply chain work," he told AFP in the United States.
"If Boeing had done a better job at that, it would not have experienced the technical problems it has, in my opinion."
The US firm is banking on strong global demand for an all-new design based on lightweight composite materials that is much more fuel-efficient than older aircraft. It has won orders for nearly 850 more 787s.
All of the 50 Dreamliners already flying -- in Chile, Ethiopia, India, Japan, Poland, Qatar and the United States -- have now been taken out of service after a global alert issued this week by the US Federal Aviation Administration.
Boeing shares lost another 1.0 percent in US trading on Thursday and some suppliers such as GS Yuasa have also been hammered on the markets.
The US company could face demands for compensation from customers who have placed the Dreamliner at the heart of their fleet renewal plans.
Polish flag carrier LOT -- the only European operator of the 787 so far -- said it still expected to take delivery of three more planes before the end of March, provided any defects on the plane are eliminated.
Other airlines that have 787s on the production line spoke out in support of Boeing, backing its contention that there is nothing wrong with the plane beyond teething troubles.
Australia's Qantas said it was cutting its request for Dreamliner planes by one, but noted it had planned to do so before the jets were grounded and that it still had 14 on order.