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National Transportation Safety Board (NTSB) chief Deborah Hersman said Friday an upcoming hearing should reveal “a lot more about the certification and design process” that Boeing and aviation regulators used for the 787 Dreamliner battery system before it went into service.

After that, she said in an interview, “If we believe there are changes that need to be made, we will pursue that.”

Hersman said the NTSB will review Boeing’s design and risk analysis and the Federal Aviation Administration’s certification process in its final investigation report, which should be issued by the end of the year.

She spoke immediately after a two-day public forum in Washington, D.C., in which industry and government experts gave a broad overview of lithium-ion batteries in transportation, highlighting innovative design choices as well as safety issues. The hearing specifically focusing on Boeing’s batteries and the FAA’s certification is scheduled for April 23 and 24.

Hersman said the discussion made clear that while lithium-ion batteries have “tremendous potential” and the industry has made “amazing progress,” the risks must be addressed.

She declined to comment specifically on Boeing’s proposed battery fix. The NTSB is charged with assessing safety and making recommendations, but the FAA sets the rules of aviation, and it’s the agency that grounded the Boeing jets.

“Boeing has to identify and properly mitigate the risks to the FAA’s satisfaction,” Hersman said. Lifting the grounding “really is up to the FAA.”

Friday’s forum revealed that some other users of lithium-ion batteries in transportation equipment have taken different approaches than Boeing.

Speakers included Jeff Dermott, director of new product development at EaglePicher Technologies of Joplin, Mo., which is certifying a new battery design for Cessna’s business jets.

His brief description of that battery, divulged in public for the first time, suggests that while it shares with the new Boeing 787 battery design a heavy-duty outer containment box, it may be more sophisticated internally.

Dermott said the EaglePicher battery uses multiple small cells, each with a heater to promote even charging and boost cold-temperature performance.

The battery has two independent electronic-protection systems. Individual battery cells are never connected to each other and each is charged independently, he said.

Celina Mikolajczak, manager of cell quality and battery technology at Tesla Motors, described the different battery solution the high-end electric carmaker came up with: more than 7,000 small lithium-ion cells connected in parallel in the $87,000 Model S sedan, compared with eight large cells in Boeing’s batteries.

Mikolajczak said Tesla’s design ensures that if one cell overheats and goes into “thermal runaway” — something Tesla assumes will happen — the problem won’t propagate to the other cells and the driver won’t even notice.

“Our approach is to design a pack so it is a nonevent,” Mikolajczak said.

In such an in-service event, the car will communicate wirelessly with a Tesla data center, she said. “Our cars will call us and tell us there’s a problem, that the vehicle needs maintenance.”

Patrick Davis, director of the U. S. Department of Energy’s Vehicle Technologies Office, expressed the consensus among forum panelists when he said safety can be engineered into any lithium-ion battery-powered vehicle, though at some trade-off in cost and weight.

Stephen Summers, of the National Highway Traffic Safety Administration, testified that data from crashes of electric cars indicate “they pose no greater safety risk than traditional internal-combustion engines.”

Yet NTSB’s Hersman in the interview noted a Navy expert’s discussion of how lithium-ion batteries can fail in unpredictable ways.

Kevin Cook, representing the battery-safety office of the U.S. Naval Sea Systems Command, said the Navy has wide experience with advanced lithium-ion systems in manned and unmanned vehicles and weapons.

In 2008 it lost a $350 million prototype of a stealthy mini-sub that burned up in a lithium-ion battery fire during routine maintenance.

“It’s amazing how the failures are subtle and very unplanned,” Cook said. “Systems fail in ways the designers never envisaged.”

The forum on lithium-ion batteries arose out of the NTSB’s investigation of a battery fire aboard a parked 787 at Boston’s Logan Airport in January.

Interviewed Friday, Hersman addressed statements by Boeing Vice President Mike Sinnett that appeared to downplay the severity of the Boston incident and another one a week later, when a battery aboard a 787 in flight in Japan began to smolder.

“In neither event was there a fire inside the blue box of the battery,” Sinnett said in a news conference in Tokyo last month, adding that in both incidents, “the airplane was not at risk.”

Hersman said the NTSB investigation into the Boston incident showed very hot temperatures and extensive blackening inside the battery box.

“When something gets in excess of 600 degrees and you have significant damage from thermal runaway, at that point there’s a significant amount of heat damage,” she said. “Whether there was fire inside of the box or not, there was fire outside the box.”

Hersman acknowledged that it’s a challenge to identify the root cause of the internal short known to have started the Boston battery fire because the battery was severely damaged.

In searching for that cause, her experts are conducting weeks-long tests on other batteries produced by Boeing’s supplier, GS Yuasa of Japan.

“We have to let the investigation play out,” Hersman said.

Dominic Gates: (206) 464-2963 or