But to prevent any new fire and smoke episodes like the ones that have grounded its fleet, Boeing proposed the crudest tool in its considerable technological arsenal: the battery itself will be sealed inside a steel box that would serve as the last safety rampart if everything else fails.

The Federal Aviation Administration approved these changes on Tuesday, and Boeing has since begun a series of 20 certification tests that it expects to wrap up in one to two weeks. Most of the tests will be conducted inside Boeing labs, with only a single test flight planned since the plane’s two batteries are not used while in normal flight.

The 50 787s delivered to airlines so far have all been grounded since mid-January after two planes developed battery problems; one battery ignited while a plane was parked in Boston and another forced an emergency landing in Japan when it began to smoke. With significant commercial and financial stakes in the balance, Boeing is keen to rapidly resume passenger flights, though government officials have been more cautious about the timing.

But the new safety features, made public late Thursday, were an admission that despite its substantial resources, Boeing might never determine what went wrong with the batteries. Still, the changes are intended to reassure regulators and the public that the planes are safe and should be allowed to fly again soon.

“This enclosure keeps us from ever having a fire in the beginning,” Mike Sinnett, the 787’s chief engineer, said during a news conference in Japan along with Ray Conner, the president and chief executive of Boeing’s commercial airplane division. “It eliminates the possibility for fire.”

Mr. Sinnett said that Boeing engineers had identified 80 different ways that the batteries could fail and modified the batteries as a result. But if, for whatever reason, a cell did overheat and combust, the steel casing would contain the smoke and fire, the venting tube would open, and the smoke would be pushed outside the plane instead of venting inside the cabin.

Donald R. Sadoway, a materials chemistry professor at M.I.T., was not persuaded that Boeing’s plan went far enough. He said Friday that the proposals seemed intended to mollify the F.A.A. to lift the grounding of the planes, but the approach seemed to focus more on dealing with a battery failure rather than preventing one. He pointed out that automakers had developed large-format lithium-ion batteries without encountering the problems Boeing has had.

“It doesn’t have the look and feel that they are going to extreme measures to make sure this thing is robust,” he said.

The presence of senior Boeing officials in Japan reflected the central role that Japanese companies have played in financing and manufacturing the planes. Japanese authorities also need to approve Boeing’s new design.

The lithium-ion battery is made in Japan by GS Yuasa, which Mr. Conner called “a tremendous partner.”

During the presentation, Boeing also disputed characterizations made by the National Transportation Safety Board in its investigation of the Boston episode. The safety board has described it as a fire event that was caused when a failure in one cell cascaded to others, in what the board referred to as a thermal runaway. Boeing executives took issue with both assertions, contending there never was a fire inside the battery. They pointed out that the only eyewitness report referred to two three-inch flames on the connectors outside the battery box. The second episode involved only smoke.

In a report last week, the safety board said that firefighters reported “radiant heat waves” along with considerable smoke, but no flames, and one firefighter was burned in the neck when the battery exploded.

In response, a safety board spokeswoman said the board stood by its report and would “release only factual information as we are able to corroborate it.”

Boeing’s stock closed at $86.43 on Friday, up 2.14 percent.

Boeing’s solution, which company officials call comprehensive and permanent, involves using the same battery cells and blue-box aluminum casing. The cells from the existing batteries will be retested and repurposed.

The batteries’ original insulation made of polyvinyl chloride, or PVC, can withstand heat of 300 degrees Fahrenheit. Instead, the cells will be wrapped with another insulating material called phenolic glass laminate, made of thin layers of a fiberglass material and resin, with a resistance of more than 900 degrees.

Boeing is also taking steps to reduce vibrations inside the battery that might have been one of the possible causes of the short circuits.

The changes to the two batteries will add 150 pounds to the weight of the airplane — a small addition to the 350,000 pound jet — but enough to offset the weight advantage from using the lighter lithium-ion batteries in the first place.  

Boeing said it had been testing its new system for the last six weeks and found that the steel casing could withstand three times the pressure generated when a battery suffered a catastrophic failure.

“We think the likelihood of a repeat event is very unlikely,” Ron Hinderberger, a senior Boeing 787 engineer, said on a conference call on Friday.

Article source: http://www.nytimes.com/2013/03/16/business/boeing-details-its-fixes-for-787.html?partner=rss&emc=rss