The chairwoman of the National Transportation Safety Board today provided an update into the NTSB’s ongoing investigation into battery problems with the Boeing 787 Dreamliners.

The agency is looking into the cause of an auxiliary power unit battery that burned onboard a Japan Air Lines Boeing 787 on Jan. 7 at Boston’s Logan International Airport. No passngers were on the plane at the time. The entire fleet of 50 Dreamliners has since been grounded by airlines and aviation authorities around the world.

“We do not expect to see fires on aircraft,” NTSB Chairwoman Deborah Hersman said during a news conference in Washington today.

The NTSB has determined the Dreamliner batteries were experiencing problems with thermal runaway and short circuiting, Hersman said.

She said the agency is taking the problmem very seriously and devoting a lot of effort to determining what went wrong with the batteries. “We have all hands on deck,” she said.

Hersman described the grounding of the 787 fleet as an unprecedented event. “This is a very serious air safety concern.”