WASHINGTON — The National Transportation Safety Board indicated Thursday that an investigation into the failure of lithium-ion batteries aboard two Boeing 787 planes is still far from determining a cause.
Deborah A.P. Hersman, chairwoman of the board, said a battery that caught fire in a 787 parked at a gate at Logan International Airport in Boston showed signs of short-circuiting and of a ‘‘thermal runaway,’’ in which a chemical reaction begins to overheat the battery and speeds up as the temperature increases. But Hersman described these as ‘‘symptoms,’’ and pointedly declined to say whether those problems were the cause of the incident, which, combined with a similar event in Japan, has led to the grounding of all 50 of the planes in service.
“These are all symptoms that something’s wrong,’’ she said. ‘‘Understanding what came first and what triggered the next thing, that’s information we are working to identify.’’
While there were no deaths or injuries, she said, ‘‘These events should not happen.’’
“There are multiple systems to prevent against a battery event like this,’’ she said. ‘‘Those systems did not work as intended. We need to understand why.’’
Hersman highlighted the seriousness of the problems more bluntly than other officials have, and her comments made clear that Boeing will not be able to get its planes back in the air anytime soon.
The battery damage was so significant, she said, that investigators are having difficulty retrieving information from the battery control system.
Japanese aviation authorities are leading the investigation into the second battery incident, which occurred earlier this month on a 787 flown by All Nippon Airways. It made an emergency landing in Japan after its pilot reported a burning smell in the cockpit while smoke alarms rang.
Hersman’s briefing, the first by the safety board on the batteries, fleshed out some of the questions facing engineers
With 50 airplanes grounded and Boeing’s marquee new product in limbo, engineers working for Boeing, its suppliers, and government agencies in this country and in Japan are scrambling to determine what happened. But Hersman was not making any promises.
“It is really very hard to tell at this point how long the investigation will take,’’ she said. ‘‘What I can tell you is we have all hands on deck. We are working hard to determine what the failure mode here is and what actions have to be taken.’’