By Antoni Slodkowski and James Topham
TOKYO (Reuters) - A device seen as key to explaining why a Boeing Co
Circuit boards that control and monitor the performance of the plane's lithium-ion battery unit were charred and may be of little use to the teams investigating why the battery effectively melted, forcing safety investigators to scramble for possible clues from other components in the plane's electronics, said the person, who didn't want to be named as the probe is ongoing.
Aviation authorities in Japan face a painstaking reconstruction that may take months before they can unravel what caused one of the batteries to overheat, triggering warnings in the plane's cockpit.
That relatively inexpensive circuit boards may be keeping $10 billion worth of futuristic aircraft idle underscores how dependent the Boeing jet is on advanced electronics rather than more traditional, but less fuel-efficient, parts, experts said.
"The circuit board (system) is badly damaged. We'll see how much we can learn from examining it, but we'll also have to look at other recording devices on the aircraft to try and find out what happened," the person with direct knowledge of the investigation told Reuters.
The circuit boards, known as the battery monitoring unit, are the "brains" of the battery, experts said. About the size of a laptop computer, the boards monitor functions of the lithium-ion battery's eight cells and feed this information to the charger. That effectively makes the boards responsible for preventing a battery from overcharging.
One key question for safety investigators is how the battery's eight individual cells became volatile even though the overall voltage to the battery was steady and didn't exceed the 32-volt capacity, officials have said. That data is not recorded in the Dreamliner's "black box" flight-data recorder.
U.S, Japanese and Boeing representatives have this week been at the Kyoto headquarters of GS Yuasa Corp <6674.T>, which makes batteries for the 787, looking at everything from manufacturing quality to technical standards.
The main battery from the All Nippon Airways <9202.T> flight is still at the GS Yuasa plant, where it is being cleaned and disassembled for further checks. Once they are done, Japanese safety officials plan to take the damaged circuit boards to the manufacturer, Fujisawa-based Kanto Aircraft Instrument, for a detailed inspection.
All 50 of Boeing's Dreamliners in service were grounded last week after the ANA-operated flight's emergency landing on a domestic flight. That followed an auxiliary battery fire in a Japan Airlines Co Ltd <9201.T> 787 parked at Boston Airport.
"There is a possibility that a fire destroyed the elements that caused the problem and if so, it will become difficult to investigate the cause," said Hideaki Horie, project professor at the Institute of Industrial Science at Tokyo University.
Horie said Boeing should re-think the design of the battery safety and data recovery system even while it investigates what caused the recent Dreamliner incidents.
The 787 uses two lithium-ion batteries, which are about twice as large as a car battery. The batteries weigh less than a conventional battery and provide more power. They are Boeing's first step towards hybrid power systems like those used by automakers General Motors Co
(Additional reporting by Maki Shiraki and Mari Saito; Editing by Ian Geoghegan)