The National Transportation Safety Board on Thursday released 547 pages of reports and supporting materials about its investigation of the Boeing 787 battery fire Jan. 7 in Boston.
The documents show firefighters struggling to tame a small but worrisome fire that has left investigators relieved that it happened after a flight and not during one.
Another smoldering battery nine days later in Japan prompted the grounding of 50 787s worldwide. Investigators still don’t know the root cause.
Other than the firefighter’s injury, neither incident hurt anyone. But fire is a major threat to any airplane’s safety.
Before the incidents, Boeing categorized flame from the 787 battery as “catastrophic,” prompting it to build in extra safeguards designed to prevent a battery fire.
It was thought that the only way the battery would burn would be if it was overcharged, according to one NTSB report, which cited Boeing’s earlier testing.
Boeing estimated the likelihood of a smoke incident as one in every 10 million flight hours for the 787 fleet.
In January there were two when the fleet had only 52,000 hours.