US safety officials investigating burned batteries on two Boeing Co’s 787s on Tuesday said they are not certain what caused the incidents, even as aviation regulators approve Boeing’s fix for the problem.
Four days after the US Federal Aviation Administration (FAA) cleared the 787 to return to flight, the US National Transportation Safety Board (NTSB) opened a two-day public hearing to examine how the pioneering lithium-ion battery system was designed and approved for use.
At the end of the first day, National Transportation Safety Board chairwoman Debbie Hersman said they heard new information on the problems.
However, she said they still do not know for certain what caused the battery problems in January which resulted in a fire on one 787 flight and smoke on another.
“We really have not reached a point where it’s appropriate to say we’ve determined cause,” Hersman told journalists.
“We have identified the origin of the event and our teams are still working right now” to find what caused the short-circuit that led to a series of uncontrolled temperature increases in multiple battery cells, she added.
Hersman said it was clear from the hearings that the original testing — in which the FAA relied heavily on Boeing itself — was inadequate.
“We also heard today that their assumptions and the testing that they did were not as conservative as they could have been,” she said. “They acknowledged that the test conditions were not as severe as they saw in service.”
The problems first surfaced publicly when a fire erupted in the battery area of a Japan Airlines 787 parked at a Boston airport on Jan. 7.
Then on Jan. 16, battery fumes forced an emergency landing of an All Nippon Airways 787 in Japan, forcing the grounding of all 50 of the aircraft in service worldwide.
On Friday last week, the FAA approved Boeing’s new design to make the battery safer and flights will be allowed after each aircraft is modified with the fix.
On Tuesday, the European Aviation Safety Agency announced its approval of the Boeing battery system modifications.
Japanese regulators on Tuesday said they would make a final decision on allowing the 787 to fly after this week’s NTSB hearings.