Dreamliner probe results 'weeks away,' NTSB chief says

WASHINGTON (Reuters) - The National Transportation Safety Board is "probably weeks away" from completing its probe into battery problems on the Boeing 787 Dreamliner and will share its latest information about the jet on Thursday, NTSB chairman Deborah Hersman said.

"We will talk about special conditions that were put into effect at the time when the Dreamliner was certified," Hersman told reporters at a Wednesday breakfast briefing hosted by the Christian Science Monitor.

All 50 Dreamliners in service have been grounded since January 16 while the NTSB, U.S. Federal Aviation Administration and other aviation regulators around the world investigate the battery failures that included one fire. No root cause has been identified.

Fire risk on planes has always been a major concern, especially given the amount of fuel they carry and the heat generated by jet engines. U.S. aviation standards require planes to have numerous on-board fire-suppression systems.

The FAA in 2007 granted the Dreamliner special conditions and said its contain-and-vent system was sufficient to control the build-up of explosive or toxic gases, except in situations considered "extremely remote."

That decision has come under scrutiny after the lithium-ion batteries in two 787 planes failed within days of each other, sparking a fire in one jet in Boston and generating warnings and an acrid smell that prompted the pilots of the second plane to make an emergency landing in Japan.

The NTSB is conducting the U.S. probe with help from Boeing, battery maker GS Yuasa Corp of Japan, the FAA and battery experts from other U.S. federal agencies, but none of the agencies have yet identified what caused the battery failures on the 250-passenger airliner.

Boeing this week asked the FAA for permission to conduct test flights of the 787, suggesting it is making progress in finding a solution to the battery problems, but the government agency has not yet announced a decision.

"In essence what happens when an aircraft is certified, it basically gets locked into the standards that are in existence at the time. So the question ... is whether or not as time goes on through the life of the aircraft, do they fly with new standards?" Hersman said.

Hersman declined to comment on a report that she was the White House's top choice to be the next transportation secretary, saying she was focused on her current job.

Hersman said the NTSB has been looking at the risks of lithium-ion batteries for some time and has recommended strategies to reduce potential hazards.

She said that there will always be advances in technology, but the safety side of that is "to make sure you've done the right risk assessment, that you understand what the failure modes are and that you've mitigated any potential risks."

"I would not want to categorically say that these batteries are not safe. Any new technology, any new design, there are going to be some inherent risks. The important thing is to mitigate them," she said.

(Reporting by Doug Palmer; Editing by Doina Chiacu and Philip Barbara)