By Keith Laing - 02/07/13 10:15 PM EST
"Boeing assessed that the likelihood a smoke emission event from a 787 battery would occur less than once in every 10 million flight hours," Hersman said.
"The 787 fleet has accumulated less than 100,000 flight hours, yet there have now been two battery events, results in smoke, less than two weeks apart, on two different aircrafts," she continued. "The assumptions that were used to certify the battery must be reconsidered."
The 787 was grounded by the FAA after a fire broke out on an airplane that was being operated by Japan Airlines at Boston's Logan International Airport. Other worldwide aviation agencies quickly followed the FAA's lead, resulting in a worldwide grounding of the Dreamliner that has lasted for nearly a month.
Hersman said Thursday that the NTSB's investigation of the battery that was involved has revealed that it experienced a short circuit that led to accelerated temperature increases known as "thermal runaway."
Boeing called the development "a narrowing of the focus of the investigation to short circuiting observed in the battery."
The company added that it "remains committed to working with the NTSB, the U.S. Federal Aviation Administration (FAA) and our customers to maintain the high level of safety the traveling public expects and that the air transport system has delivered.
"We continue to provide support to the investigative groups as they work to further understand these events and as we work to prevent such incidents in the future," Boeing said. "The safety of passengers and crew members who fly aboard Boeing airplanes is our highest priority."