US agencies clear Boeing 787 Dreamliner test flights: Report
Hersman said the short-circuit was caused in cell number six of the battery which was the root cause of the fire.
"At this time, we've been able to rule out two possible causes. We have ruled out the mechanical impact damage to the battery. All mechanical damage to the cells and the
battery case occurred after the initiating the short-circuiting in cell number six," she said.
The board, in its probe, has also ruled out external short-circuiting of the cells or battery, she said, adding several potential causes for the short-circuiting in cell
number six are being examined.
"We are looking for evidence of contamination, electro folds, wrinkles and pinches in the assembly of cells and the battery. And because the 787 battery is really a collection of eight individual cells packaged together in a box, we're looking at the total design of the battery", she said.
The NTSB also blamed the FAA certification process for having given approval for the battery
"Because the 787 incorporated a number of what the FAA calls 'novel or unusual design features', the applicable airworthiness regulations at the time did not address those new features."
"So as a result, in 2007, the FAA issued nine special conditions for the 787 with regard to the use of lithium ion batteries. These special conditions contained additional safety requirements that the FAA deemed necessary to ensure an
equivalent level of safety," Hersman said.