FAA says Boeing can fly Dreamliners to test batteries

• Test flights allowed over unpopulated areas
• NTSB says it knows the origin of one battery problem%2C but not the cause
• The plane has been grounded since Jan. 16

WASHINGTON — Federal transportation officials approved test flights Thursday for Boeing's 787 Dreamliner, as part of the effort to figure out why batteries failed on two of the innovative planes that have been grounded for weeks.

Transportation Secretary Ray LaHood and Michael Huerta, head of the Federal Aviation Administration, jointly announced the approval, saying the flights would be subject to extensive pre-flight testing and would occur over unpopulated areas.

The precautions include inspecting batteries and cables to ensure there is no damage, continuously monitoring batteries during the flights and flying only with essential crew.

"These test flights will be an important part of our efforts to ensure the safety of passengers and return these aircraft to service," the statement said.

Boeing said the test flights would begin "soon" and that the company considers the flights "safe." The company said hundreds of experts are working around the clock to resolve the battery problem and get the plane back in the air.

"We are working this issue tirelessly in cooperation with our customers and the appropriate regulatory and investigative authorities," spokeswoman Kate Bergman said in a statement.

The special permission for test flights came the same day as a special 787 flight from a painting facility in Texas to Washington state.

In addition, safety investigators announced that they found the origin of the short-circuit in the lithium-ion battery that caught fire aboard a Boeing 787 Dreamliner, but not yet the cause.

Deborah Hersman, head of the National Transportation Safety Board, said the Federal Aviation Administration should reconsider the special permission it gave Boeing in 2007 to use the unique battery aboard the plane.

When Boeing certified the plane, it projected from sometimes abusive testing that the batteries were expected to smoke once in every 10 million miles of flying, Hersman said. But after two battery problems in the first 100,000 hours of flying, she says nine special conditions that the FAA set on Boeing to use lithium batteries in the plane need to be reconsidered.

"The assumptions used to certify the battery must be reconsidered," Hersman says. "We know that some of the assumptions that were made to make sure they didn't have a smoke event were not met, much less a fire event."

FAA Administrator Michael Huerta announced a full review of the plane's manufacture and design on Jan. 11, just after the battery fire on a Japan Airlines 787 parked in Boston.

Huerta and Transportation Secretary Ray LaHood issued a joint statement Thursday saying that the agency must complete its comprehensive review of the 787 before deciding what changes or improvements to make.

"The leading experts in this field are working to understand what happened and how we can safely get these aircraft back into service," the statement said. "As the agency said last month, the FAA is focused on the review and activities to understand the root cause. Once the review is complete, the FAA will make any analysis and conclusions public."

Boeing shares traded higher on the news, closing up 1.5% to $77.43.

On Jan. 16, the FAA and other regulators around the world grounded the 50-plane fleet after an All Nippon Airways 787 made an emergency landing in Japan because of a smoldering battery.

In pinpointing the origin of the Boston fire, Hersman said the short-circuit in one of eight cells in the battery led to a chemical reaction called a "thermal runaway" that sparked the fire.

Investigators are now looking at the charge going to the battery, the manufacturing including any possible contamination and the design such as how tightly packed the cells are.

"A short-circuit did occur, it resulted in cell-to-cell propagation in a cascading manner and a fire," Hersman said.

Hersman said the safety board will issue a factual report in 30 days but that it might not reach conclusions about what caused the fire.

"I don't expect that to be reaching a conclusion for the investigation," Hersman said.

She couldn't yet draw any comparisons between the batteries that failed in Boston and Japan, or whether they failed in the same way.

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The grounding is expected to last weeks longer for passengers. United Airlines, the only U.S. airline to have the Dreamliner, said Wednesday that it has replaced its six 787s with other planes through the end of February.

All Nippon Airways on Wednesday canceled its 787 flights through March 30.

The batteries were used because they are lighter and recharge more quickly than other types of batteries and contribute to the plane being 20% more fuel efficient than its rivals.