NEW YORK – The U.S. National Transportation Safety Board said it is examining whether the Boeing 787’s lithium-ion battery problems were due to formation of microscopic structures called dendrites, which can cause overheating.
The battery problems caused all Dreamliners to be grounded last month.
Dendrites are tiny deposits of lithium that can grow inside a battery’s cells. They can cause short circuits, heat or even fire.
On Jan. 16, the 50 Dreamliners in service around the world were grounded after a battery fire on a Japan Airlines plane parked in Boston, and battery smoke on an All Nippon Airways flight forced an emergency landing in Kagawa Prefecture.
“As part of our continuing investigation, we are certainly looking at whether dendrites may or may not have been a factor” in the faulty batteries, NTSB spokeswoman Kelly Nantel said Monday.
She did not say if dendrites had been found, and stressed that investigators were still considering several potential causes for short-circuiting that was observed.
“They include looking at the state of charge of each individual cell and the method and delivery of that charge, looking for evidence of contamination, electrode folds, wrinkles and pinches and the assembly of the cells and battery and looking at the total design of the battery, including the physical separation of the cells, their electrical interconnections, and their thermal isolation from each other,” Nantel said in an email.
The NTSB, which is probing the Boston incident in particular, said last week it had focused on how the fire spread in the battery, rather than on the cause of it.
Boeing declined comment Monday. Boeing conducted a second test flight of a 787 on Monday as it looks for the cause of battery problems that have grounded the planes. It said no more tests are currently planned.
Boeing said the flight lasted one hour and 29 minutes and was uneventful. Flight-tracking service FlightAware showed that the plane flew from Boeing Field in Seattle, east over Washington state, and back.
Boeing won permission from the Federal Aviation Administration last week to conduct test flights under special conditions, including that the planes fly over unpopulated areas.
Boeing said Monday’s flight included two pilots and 11 flight test personnel. The test plane includes special equipment that lets it track the conditions of its two big lithium-ion batteries during the flight. It’s one of Boeing’s fleet of six 787 test planes that were used for flight testing before the plane went into full production.
JAL cancels more flights
Japan Airlines Co. said Tuesday it will cancel 38 flights on two of its international routes from March 1 to 30 due to the global grounding of all Boeing 787s.
An estimated 3,020 passengers are expected to be affected by the cancellations on the routes linking Narita International Airport with Boston and San Diego, JAL said.