WASHINGTON – The U.S. government should reassess its safety approval of Boeing Co.’s 787 lithium-ion batteries, the top U.S. accident investigator said Thursday, casting doubt on whether the Dreamliner’s troubles can be remedied quickly.
Switching to a different type of battery would add weight to the plane — and fuel efficiency is one of the 787′s main selling points.
Boeing received permission Thursday to conduct test flights under limited circumstances with special safeguards — a critical step toward resolving the plane’s technical problems. The global 787 fleet has been grounded for the past three weeks, and Boeing needs to be able to test the batteries under flight conditions before a solution can be approved.
The flights will be conducted over unpopulated areas and extensive preflight testing and inspections and in-flight monitoring are required, the U.S. Federal Aviation Administration said in a statement Thursday.
The U.S. National Transportation Safety Board is investigating last month’s battery fire in a Japan Airlines Corp. 787 Dreamliner while it was parked in Boston. The results so far contradict some of the assumptions that were made about the battery’s safety at the time the system won approval from the federal government, NTSB Chairwoman Deborah Hersman told reporters at a news conference.
The board’s investigation shows the fire started with multiple short-circuits in one of the lithium-ion battery’s eight cells, she said. That created an uncontrolled chemical reaction known as “thermal runaway,” which is characterized by progressively hotter temperatures, spreading the short-circuiting to the rest of the cells and causing the fire, she said.
According to Hersman, the findings are at odds with what Boeing told the FAA when the agency was working to certify the manufacturer’s newest and most technologically advanced plane for flight. Boeing said its testing showed that even when trying to induce short-circuiting, the condition and any fire were contained within a single cell, preventing thermal runaway and fire from spreading.
Boeing’s testing also showed the batteries were likely to cause smoke in only 1 in 10 million flight hours, she said.
But the fire aboard the JAL 787 at Boston’s Logan International Airport was followed nine days later by a smoking battery in an All Nippon Airways Co. Dreamliner that made an emergency landing at Takamatsu Airport in Kagawa Prefecture. The global 787 fleet has recorded less than 100,000 flight hours, Hersman noted.
The plane that caught fire in Boston was delivered to JAL less than three weeks before the fire and had recorded only 169 flight hours over 22 flights.
“There have now been two battery events resulting in smoke less than two weeks apart on two different aircraft,” Hersman said. “This investigation has demonstrated that a short-circuit in a single cell can propagate to adjacent cells and result in smoke and fire. The assumptions used to certify the battery must be reconsidered.”
All 787s have been grounded since Jan. 16. With no end in sight, the halt has become a nightmare for Boeing, which has about 800 orders for the plane from airlines around the world. The company’s customers were already frustrated that the Dreamliner was more than three years late when the first one was delivered toward the end of 2011.
Boeing loses money on each 787 it delivers, and the cash burn grows with each missed delivery, analysts say.
Investigators are still trying to determine why the first battery cell short-circuited, but the board’s findings appear to raise doubts about the thoroughness of the FAA safety certification of the 787′s batteries and whether Boeing can remedy the problems with the addition of a few quick safeguards.
“We must finish (our review) before reaching conclusions about what changes or improvements the FAA should make going forward,” U.S. Transportation Secretary Ray LaHood and FAA Administrator Michael Huerta said in a joint statement Thursday. “The leading experts in this field are working to understand what happened and how we can safely get these aircraft back into service.”
But John Goglia, a former NTSB board member and aviation safety expert, said the board’s findings mean the U.S. government will likely require Boeing to re-certify the batteries, noting: “Certifications aren’t exactly painless and quick. It could be a big, drawn-out thing.”
The significance of the NTSB’s findings “is if this can happen — and the safety analysis assumed that it would not happen — then the safety analysis is no longer valid,” said Jon Hansman, a Massachusetts Institute of Technology aeronautics professor and a member of the FAA’s Research and Development Advisory Committee.
Battery experts said Boeing could try to build more safeguards into the battery by using a greater number of smaller cells and putting more insulation between them. Or, they said, the aircraft maker could switch to a different type of lithium-ion battery already approved for aviation. Some business jets use lithium-ion batteries as their main batteries.
They said switching to another type, such as lead-acid or nickel-cadmium batteries, is another possibility, but that would involve changing the charging system as well. The new batteries — and, presumably, a revised charging system — would need to be designed and tested by Boeing and approved by the FAA before they could be installed.
The same day as the emergency landing at Takamatsu Airport, FAA officials ordered the only U.S. carrier with 787s — United Airlines, which has six of the planes — to ground them. Aviation authorities in other countries swiftly followed suit and in all, 50 planes operated by seven airlines in six countries have been grounded.
The 787 is the first airliner to make extensive use of lithium-ion batteries. Besides being lighter, the batteries recharge faster and can store more energy than other types of batteries of an equivalent size, and can be molded to fit into odd spaces on planes. The Airbus A350, slated for completion in 2014, will also make extensive use of lithium-ion batteries. Manufacturers are also looking to retrofit existing planes, replacing other types of batteries with lithium-ion cells.
But these batteries in general are more likely to short-circuit and start a fire than others if they are damaged, if there is a manufacturing flaw or if they are exposed to excessive heat. In 2007, the FAA issued special conditions that Boeing had to meet in order to use lithium-ion batteries in the 787, because at that time the agency’s safety regulations didn’t include standards for such battery systems.
The 787 relies to a greater extent than any previous airliner on electrical systems, as opposed to hydraulic or mechanical ones. The batteries help run those electrical systems and also are used to start a power-generating engine in the rear of the aircraft.
The batteries are made by Kyoto-based GS Yuasa Corp. Japanese aviation investigators probing the cause of the ANA battery failure have also found there was thermal runaway.
Investigators have ruled out mechanical damage or external short-circuiting as possible causes of the initial, internal battery short-circuiting, according to the NTSB’s Hersman. Investigators and technical experts are now looking for evidence of flaws inside the batteries, like pinches, wrinkles or folds.
“We are looking at a number of scenarios,” Hersman said, including the state of charge of the battery, its manufacturing processes and the design of the batteries. “We haven’t reached any conclusions at this point. We really have a lot of work to do.”