Boeing will start test flights under limited circumstances with special safeguards.
WASHINGTON—The US government should reassess its safety approval of the Boeing 787’s lithium ion batteries, America’s top accident investigator said, casting doubt on whether the airliner’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 has received permission to conduct test flights under limited circumstances with special safeguards. The company 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 pre-flight testing and inspections and in-flight monitoring are required, the Federal Aviation Administration said in a statement.
The National Transportation Safety Board is investigating last month’s battery fire in a Japan Airlines 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 government approval, said the board’s chairwoman, Deborah Hersman.
The NTSB investigation shows the fire started with multiple short-circuits in one of the battery’s eight cells, creating an uncontrolled chemical reaction known as “thermal runaway,” which is characterized by progressively hotter temperatures. That spread the short-circuiting to the rest of the cells and caused the fire, she said.
The findings are at odds with what Boeing told the FAA when that agency was working to certify the company’s newest and most technologically advanced plane for flight, Hersman said. 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, she told reporters at a news conference.
Boeing’s testing also showed the batteries were likely to cause smoke in only 1 in 10 million flight hours, she said. But the Boston fire was followed nine days later by a smoking battery in an All Nippon Airways plane that made an emergency landing in Japan. The 787 fleet has recorded less than 100,000 flight hours.
The plane that caught fire in Boston was delivered to Japan Airlines 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.”
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 FAA’s safety certification of the 787’s batteries and whether Boeing can remedy the problems with the addition of a few quick safeguards. The FAA typically delegates testing of new aircraft designs to the manufacturer, while overseeing that the tests meet the agency’s requirements. The agency also relies to some degree on the expertise of the manufacturer’s engineers, especially in the case of a cutting-edge plane like the 787.
Following the fire at Boston’s Logan International Airport, Transportation Secretary Ray LaHood and FAA Administrator Michael Huerta ordered a review of the 787’s design, certification, manufacture and assembly. That review is still under way.
But John Goglia, a former NTSB board member and aviation safety expert, said NTSB’s findings mean the government will likely require Boeing to re-certify the batteries.
“Certifications aren’t exactly painless and quick,” he said. “It could be a big, drawn-out thing.”
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.
Switching to another type of battery, such as lead-acid or nickel-cadmium battery, is another possibility, but that would involve changing the charging system as well, they said. 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.
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 GS Yuasa of Japan. 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, Hersman said. 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.”
©The Associated Press