Boeing’s new battery design includes better protection in case a battery overheats. The F.A.A. could still demand changes if problems develop in the laboratory and flight tests. While Boeing hopes to begin fitting its redesigned batteries in the grounded 787 fleet by mid- to late April and resume commercial flights quickly after that, government officials are not sure the process will move that fast.

Still, the decision to start the tests is a big step in Boeing’s efforts to put the innovative jets back in the air. The 50 787s delivered to airlines have been grounded since mid-January after two planes developed battery problems — one battery ignited while the plane was parked in Boston and another forced an emergency landing in Japan when it began to smoke.

Since then, Boeing engineers have scrambled to insulate the eight cells in each battery, build a sturdier battery case and create a smoke-venting system to quell concerns about the battery’s safety and persuade regulators to lift the grounding order.

Federal and industry officials said the new plan included fiberglass-like insulation between the battery’s cells to keep a short circuit in one cell from cascading to the others. They said the batteries would be enclosed in stainless steel boxes, more resistant to higher temperatures than the earlier aluminum ones. Boeing also plans to create tubes made of titanium to vent any hazardous gases outside the plane.

Adding insulation would space the cells farther apart to keep the plane’s vibrations from bringing them into contact. Boeing would also add systems to monitor the temperature and activity in each cell.

But the new plan, which calls for 20 tests that would place the battery under stress, could also sharpen a debate among some safety experts over how certain Boeing and the F.A.A. can be that the changes will eliminate the risk of smoke or fire in the batteries. Investigators in the United States and Japan have not been able to determine the precise cause of the battery problems.

“This comprehensive series of tests will show us whether the proposed battery improvements will work as designed,” said Ray LaHood, the transportation secretary. “We won’t allow the plane to return to service unless we’re satisfied that the new design ensures the safety of the aircraft and its passengers.”

The National Transportation Safety Board has found that in the Boston episode, a short circuit in one cell caused the battery to overheat and burst into flame on Jan. 7.

But investigators in Japan have raised the possibility that a battery on another 787 nine days later started smoldering because it might have been hit by a surge of electrical current from another part of the plane.

Jay F. Whitacre, an associate professor of materials science and engineering at Carnegie Mellon University, said Boeing’s approach was technically reasonable even if the cause of the battery fire was not known. Boeing’s system, he said, was designed to contain any failure of a single cell and prevent it from spreading to the rest of the plane.

“They are taking a systemic approach, and not a find-the-problem approach,” he said. “They also recognize that figuring out what went wrong is a very complicated question, like a crime scene investigation. Meanwhile, they are focused on getting the planes back in the air.”

But not everyone was comfortable with this approach.

“I think the real issue here is to develop a robust storage system that is immune to fire,” said Donald R. Sadoway, a materials chemistry professor at M.I.T. “I am not hearing anything about how to make that battery fire-resistant.”

The long-awaited announcement by the F.A.A. helped propel Boeing’s stock on Tuesday to $84.16, a five-year high. The confidence of investors was also buoyed by earlier reports of a $15 billion order by Ryanair for 170 single-aisle 737s and Boeing’s decision to move forward with a new version of its best-selling twin-aisle 777.

Article source: http://www.nytimes.com/2013/03/13/business/faa-backs-boeing-plan-for-battery-test.html?partner=rss&emc=rss