The National Transportation Safety Board (NTSB) in the U.S., investigating the cause of a fire on a Boeing Dreamliner 787 parked at Boston Logan Airport in January, transitioned its work from a macroscopic study to a microscopic examination, including chemical and elemental analysis of the areas of internal short circuiting and thermal damage. Soon after launching a microscopic investigation, NTSB officials pinpointed the cause of the fire: a lithium-ion (Li-ion) battery.
Now that other avionics onboard the 787 have been ruled out as the cause of the fire, attentions turn to the entire battery structure. In the course of their investigation into the cause of the initiating short circuit, the NTSB is dissecting the battery and carefully scrutinizing each internal and external component.
NTSB Chairman Deborah A.P. Hersman said that potential causes of the initiating short circuit currently being evaluated include: battery charging, the design and construction of the battery, and the possibility of defects introduced during the manufacturing process.
NTSB personnel first ruled out mechanical impact damage to the battery and external short circuiting as the cause. They also concluded that the deformation of and electrical arcing on the battery case were not related to the cause, but rather occurred as a result of the battery malfunction.
“There were short circuits in cells of the battery and there was a thermal runaway in the battery, multiple cells where we saw uncontrolled chemical chain reaction,” Hersman explains. “Those features are not what we would have expected to see in a brand-new battery in a brand-new airplane.”