U.S. investigators have identified some of the “symptoms” of the recent fiery battery malfunction in a Japan Airlines Boeing 787 parked in Boston but not the underlying sickness, a top safety official said Thursday.

And that’s not good news for Boeing or its airline customers, according to longtime followers of the troubled Dreamliner program.

“Real simple: They don’t have a clue what happened, they don’t know what the fix is going to be, they don’t know how long it will take to fix it, and the airplane is going to be on the ground for an indefinite period of time,” said Scott Hamilton of Issaquah, Wash.-based aviation consulting firm Leeham Co. “That’s the bottom line.”

At an afternoon press conference broadcast from Washington, National Transportation Safety Board Chairman Deborah Hersman confirmed that there were short circuits and thermal runaway, or an uncontrollable rise in temperature, in the plane’s auxiliary power unit battery. But what caused the Jan. 7 incident is still “a very open question,” she said.

“We are early in our investigation,” Hersman said. “We have a lot of activities to undertake.”

The fire, which occurred just minutes after 173 passengers exited the new, twin-aisle jet, was the first in a series of incidents this month that prompted the Federal Aviation Administration to initiate a comprehensive review of the program.

A somewhat similar incident, a smoky battery that caused an All Nippon Airways 787 to make an emergency landing, prompted those Japanese airlines, then the FAA, then aviation authorities and airlines around the world to ground all Dreamliners.

Hamilton noted U.S. Transportation Secretary Ray LaHood’s statement last week that the planes won’t fly until his department is “1,000 percent” sure they are safe, to support the assumption that the FAA won’t allow the Dreamliners to resume operations until the NTSB has determined a cause.

“He staked out a pretty hard line in the sand,” Hamilton said.

In addition to the regulatory reviews, the U.S. Senate plans to hold hearings to look at the incidents and the FAA’s certification of the plane. Asked about certification Thursday, Hersman said the incidents should not happen.

“Those designs did not work as intended,” she said. “We need to understand why.”

In a statement released Thursday evening, Boeing said it has “formed teams consisting of hundreds of engineering and technical experts who are working around the clock with the sole focus of resolving the issue and returning the 787 fleet to flight status.”

“We are working this issue tirelessly in cooperation with our customers and the appropriate regulatory and investigative authorities,” the company statement said. “The safety of passengers and crew members who fly aboard Boeing airplanes is our highest priority.”

Dreamliner’s problems

Boeing’s 787 boasts a wide variety of technological advances that makes it fuel-efficient and pleasant to fly, but the plane program has been hamstrung for years by glitches.

Parts of the 787 come from all over the world — the batteries in question are special to the 787 and made in Japan — and the jets finally come together in North Charleston and Everett, Wash.

Fifty Dreamliners have been delivered to eight airline customers, including four S.C.-built planes to Air India. All those planes have been grounded, and deliveries have been suspended.

While laying out her agency’s findings to date, Hersman noted the significance of the two battery incidents and called the FAA grounding “unprecedented.”

“We are very concerned,” she said. “We do not expect to see fire events on board aircraft.”

NTSB investigators have performed various tests on the battery, including computed tomography (CT) scans, and will continue to look for irregularities while testing “exemplar” batteries.

While the battery monitoring unit was too badly destroyed to be useful, the NTSB hopes to learn more from the plane’s flight data recorder. Investigators also are looking at the records of the battery manufacturer, GS Yuasa.

Describing the Boston incident, Hersman said the plane’s auxiliary power unit battery “was spewing molten electrolytes.”

Hersman said her team would be evaluating all potential scenarios that would explain what happened and could not say how long it would take for the investigation to run its course.

“We have all hands on deck,” she said.

More questions

A report last week that the batteries simply overcharged gave Boeing fans hope of a simple fix. But asked about that possibility Thursday, Hersman said her agency does not “have any data that shows that the battery was overcharged.”

She could not answer questions about whether one part of the battery could have overheated or short-circuited the whole unit, or whether the thermal runaway preceded the short circuits. She also couldn’t say whether it was just the battery that was the problem or a bad relationship with the rest of the plane’s extensive electrical system.

“We have far, far more questions than we have answers at this point,” Hamilton said.

Meanwhile, the NTSB’s counterpart in Japan is investigating the Jan. 16 in-flight incident there. The U.S. and Japanese agencies are coordinating to an extent, but Hersman said they are at different stages and haven’t been fully compared yet.

While Boeing’s stock ticked up Thursday 1.39 percent to close at $75.32, Carter Leake, who covers the aerospace and defense industries for BB&T Capital Markets and has downgraded Boeing’s stock twice recently, questioned how long Boeing can withstand the turbulence.

“I do sense we are approaching a tipping point here with the NTSB giving no comfort that the root-cause fix is at hand,” Leake said. “I think two weeks from now there’s a possibility that we still don’t have anything, and that would be a problem.”

Reach Brendan Kearney at 937-5906 and follow him on Twitter at @kearney_ brendan.