The results of a probe into the Boeing 787 Dreamliner will likely not be known for weeks, investigators have said, meaning the fleet will remain grounded for at least that long.

The National Transportation Safety Board’s chair Deborah Hersman declined to provide an update on the Japan Airlines probe findings ahead of an NTSB news conference set for today at 11:00 am (2130 IST).

“We’re probably weeks away from being able to tell people what happened and what needs to be changed,” Hersman told presspersons.

Hersman said investigators were “proceeding with a lot of care” in probing the cause of a January 7 lithium-ion battery fire on a JAL 787 that occurred as the unoccupied plane sat on the tarmac at Boston’s Logan airport.

The most concerning issues uncovered in the probe so far were short circuits and thermal runaway, a chemical reaction that produces uncontrollably rising temperatures.

“These factors are not what we expected to see in a brand-new battery,” Hersman said.

The battery problem on the JAL 787, and another battery incident on an All Nippon Airways 787 on January 16, led to the global grounding last month of all 50 Dreamliners in service until the issue is fixed.

However, a Boeing 787 will conduct a one-time ferry flight today from Texas, where it was being painted, back to the Boeing plant in the northwestern state of Washington today, the Federal Aviation Administration said.

The plane will carry no passengers, only the crew needed to operate the flight, and special attention will be paid to the battery before and during the flight, the FAA said.

The Japan Transport Safety Board, probing the battery failure that forced an emergency landing of the ANA 787 in Japan, said Tuesday there was evidence of thermal runaway but that the cause was still unknown.

The NTSB is working with the FAA and Japanese regulators, the US Defense Department, NASA, Boeing and other suppliers on the investigation.

“This is a priority for the NTSB,” Hersman said.

Hersman noted that the NTSB had been looking at lithium-ion batteries for a long time and had recommended measures to limit their risks.

The fire on the 787 in Boston “shows us there were some risks that were not mitigated, were not addressed,” she said.

Boeing has asked the FAA to allow it to conduct 787 Dreamliner test flights.

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