Battery tests may see 787s take off again
Boeing achieved a breakthrough on Tuesday when the Federal Aviation Administration approved its plan to test fixes for the battery problems that have grounded its 787 Dreamliner jets since January.
The new battery design includes better protection in case a battery overheats.
The FAA could still demand changes if problems develop in the laboratory and flight tests.
Boeing hopes to begin fitting its redesigned batteries in the grounded 787 fleet by next month and resume commercial flights quickly after that, but government officials are not sure the process will move that fast.
But the decision to start the tests is a big step in Boeing's efforts to put the Dreamliner jets back in the air.
The 50 787s delivered to airlines have been grounded since January when two of the aircraft 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.
Boeing engineers have been scrambling to insulate the eight cells in each battery, build a stronger battery case and create a smoke-venting system.
"This comprehensive series of tests will show us whether the proposed battery improvements will work as designed," said US Transportation Secretary Ray LaHood. "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 found that, in the Boston episode, a short circuit in one cell caused the battery to overheat and ignite on January 7.
But investigators in Japan have raised the possibility that a battery on another 787 nine days later started smouldering because it might have been hit by a surge of electrical current from another part of the plane.
Jay Whitacre, an associate professor of materials science 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 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 recognise that figuring out what went wrong is a very complicated question, like a crime scene investigation."
But not everyone was comfortable with this approach.
"The real issue here is to develop a robust storage system that is immune to fire," said Donald Sadoway, a materials chemistry professor at MIT. "I am not hearing anything about how to make that battery fire-resistant."
The FAA said it was continuing a review of the 787's design, production and manufacturing.
Mr LaHood said the planes "won't fly until we're 1000 per cent sure they are safe to fly".
Boeing officials said they thought they had identified the most likely ways the batteries could fail.
They said the changes would virtually eliminate the chances of future troubles and protect the plane and its passengers if a problem did arise.
Some battery experts said they would feel more comfortable if a precise cause was found and the problems that happened on the two flights in January could be replicated in a lab.