"We have not ruled anything out as a potential factor in the battery fire; there are still many questions to be answered,"said NTSB Chairman Deborah A.P. Hersman during a press conference.
Noting that there was a B-787 battery incident in Japan on Jan. 16, 2013, which is being investigated by the Japan Transport Safety Board, Hersman said, "One of these events alone is serious; two of them in close proximity, especially in an airplane model with only about 100,000 flight hours, underscores the importance of getting to the root cause of these incidents."
The investigation revealed that the battery in the B-787 fire in Boston showed signs of short circuiting, and had indications of thermal runaway, a situation in which a significant temperature increase can initiate a destructive chain reaction.
Hersman also expressed concerns about the adequacy of the systems to prevent such a fire from occurring. "The investigation will include an evaluation of how a fault that resulted in a battery fire could have defeated the safeguards in place to guard against that," said Hersman. "As we learn more in this investigation, we will make recommendations for needed improvements to prevent a recurrence."
The batteries were manufactured by GS Yuasa for the Thales electrical installation and are unique to the Boeing 787. The same battery model is used for the main airplane battery and for the battery that is used to start the auxiliary power unit, which is the one that caught fire in Boston.
Radiographic examinations of the incident battery and an exemplar battery were conducted at an independent test facility. The digital radiographs, or computed tomography (CT) scans, generated from these examinations allowed NTSB investigators to document the internal condition of the battery prior to disassembling it.
Ongoing lab work includes an examination of the battery elements with a scanning-electron microscope and energy-dispersive spectroscopy to analyze the elemental constituents of the electrodes to identify contaminants or defects.
Boeing responded to the NTSB's preliminary findings with a statement saying it welcomed the progress made thus far.
"The regulatory and investigative agencies in the U.S. and Japan have dedicated substantial resources to these investigations, and we appreciate their effort and leadership," the statement said. Boeing continues to assist the NTSB and the other government agencies in the U.S. and Japan responsible for investigating two recent 787 incidents. The company has formed teams consisting of hundreds of engineering and technical experts who are working around the clock with the sole focus of resolving the issue and returning the 787 fleet to flight status.
"In order to ensure the integrity of the process and in adherence to international protocols that govern safety investigations, we are not permitted to comment directly on the ongoing investigations. Boeing is eager to see both investigative groups continue their work and determine the cause of these events, and we support their thorough resolution." |
