WASHINGTON – It’s likely that burning lithium ion batteries on two Boeing 787 Dreamliners were caused by overcharging, aviation safety and battery experts said Friday, pointing to developments in the investigation of the Boeing incidents as well as a battery fire in a business jet more than a year ago.
An investigator in Japan, where a 787 made an emergency landing earlier this week, said the charred insides of the plane’s lithium ion battery show the battery received voltage in excess of its design limits.
The similarity of the burned battery from the All Nippon Airways flight to the burned battery in a Japan Airlines 787 that caught fire Jan. 7 while the jet was parked at Boston’s Logan International Airport suggests a common cause, Japan transport ministry investigator Hideyo Kosugi said.
“If we compare data from the latest case here and that in the U.S., we can pretty much figure out what happened,” Kosugi said.
The Federal Aviation Administration issued an emergency order Wednesday temporarily grounding the six 787s belonging to United Airlines. The Japanese carriers already had grounded their 787s, and airlines and civil aviation authorities in other countries followed suit, shutting down all 50 Dreamliners that Boeing has delivered.
Boeing said Friday it will stop delivering new 787s to customers until the electrical system is fixed. However, production is not stopping. The plane is assembled in Everett and North Charleston, S.C. Boeing has booked orders for more than 800 of the planes from airlines around the world attracted by its increased fuel efficiency.
John Goglia, an aviation safety expert and former National Transportation Safety Board member, said that if the incidents are due to overcharging batteries, that might be good news for Boeing. A flaw in the aircraft’s electronics that permits overcharging would likely be much easier to fix than having to replace the aircraft’s lithium batteries with another kind of battery, he said.
Another possibility is a manufacturing defect in the batteries themselves, said Jay Whitacre, an associate professor of materials science and engineering at Carnegie Mellon University. More than other types of batteries, lithium ion batteries rely on very thin sheets of material internally to separate the negative and positive poles. The slightest flaw can cause a short circuit, overheating the flammable electrolytes.
“It’s a delicate ecosystem that you are creating inside it and you have to manufacture it with perfect integrity,” said Whitacre. “Then you have to keep it in the right voltage range and be very safe with its environmental conditions.”
Jim McNerney, Boeing’s chairman, president and CEO, sent the company’s employees a letter Friday expressing confidence in the 787 and vowing to return the plane to service. “I remain tremendously proud of employees across the company for the decade of effort that has gone into designing, developing, building and delivering the most innovative commercial airplane ever imagined,” he said.