NTSB Finds Short Circuit in Dreamliner Battery
The agency's chairman, Deborah A.P. Hersman, said its investigators are focused on the design and certification requirements of the lithium-ion battery.
The international investigation of fires in two Boeing Dreamliner 787s' lithium-ion batteries took a dramatic turn Feb. 7 when the National Transportation Safety Board's chairman announced investigators have identified multiple signs of short circuiting in cell 6, one of eight individual cells in the battery that caught fire Jan. 7 on a Japan Airlines aircraft parked at Boston's Logan Airport. There was a thermal runaway of that cell that cascaded to the other cells, according to the agency, which said an external short circuit and mechanical damage have been ruled out. They're looking at the total design of the battery and checking for contamination, electrode folds or wrinkles, and how the cells and battery are assembled.
Charred battery components indicate the temperature inside the battery case surpassed 500 degrees, NTSB's news release states.
NTSB Chairman Deborah A.P. Hersman said all of the NTSB findings are being shared with Boeing, the FAA, the Japan Transport Safety Board, and France's aviation accident investigative agency, the Bureau d'Enquetes et d'Analyses pour la securite de l'aviation civile (BEA).
"U.S. airlines carry about two million people through the skies safely every day, which has been achieved in large part through design redundancy and layers of defense," said Hersman. "Our task now is to see if enough -- and appropriate -- layers of defense and adequate checks were built into the design, certification, and manufacturing of this battery."
Boeing's tests during certification of the Dreamliner found no evidence of cell-to-cell propagation or fire, according to NTSB.
Saying Boeing had determined the likelihood of a smoke emission event from a 787 battery would occur less than once in every 10 million flight hours, Hersman noted two critical battery events have occurred with fewer than 100,000 flight hours by all Dreamliners that were in service before they were grounded. She said, "the failure rate was higher than predicted as part of the certification process, and the possibility that a short circuit in a single cell could propagate to adjacent cells and result in smoke and fire must be reconsidered."
She said NTSB will release an interim report of its factual findings within 30 days.
Her comments about certification called into question FAA's decisions about the aircraft, and Transportation Secretary Ray LaHood and FAA Administrator Michael Huerta posted a statement in response: "DOT is focused on the safety of the traveling public. From day one, we have said that the comprehensive review of the Boeing 787 and the root cause analysis of the two battery incidents would be a data-driven process. Based on what information our experts find, the FAA will take any action necessary to further ensure safety. We must finish this work before reaching conclusions about what changes or improvements the FAA should make going forward. The leading experts in this field are working to understand what happened and how we can safely get these aircraft back into service. Last month, we announced a comprehensive review of the 787's critical systems including the aircraft's design, manufacture and assembly. Since then, the FAA's team of technical experts has been working around the clock to understand what happened and how best to prevent these issues from recurring. As part of this effort, the FAA is looking at both the certification process and specifically at the required tests and design of the aircraft's lithium ion battery. The FAA invited the NTSB to observe this FAA-led process. The FAA is also lending our technical experts to support the NTSB's investigation into the probable cause of the battery incidents. The agency will also evaluate information from the investigations of these incidents and will take action as appropriate. As the agency said last month, the FAA is focused on the review and activities to understand the root cause. Once the review is complete, the FAA will make any analysis and conclusions public."
Boeing posted a statement in response to the findings saying it "welcomes the progress" made by NTSB in its investigation. "The findings discussed today demonstrated a narrowing of the focus of the investigation to short circuiting observed in the battery, while providing the public with a better understanding of the nature of the investigation," it said. "The company 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. The safety of passengers and crew members who fly aboard Boeing airplanes is our highest priority. The 787 was certified following a rigorous Boeing test program and an extensive certification program conducted by the FAA. We provided testing and analysis in support of the requirements of the FAA special conditions associated with the use of lithium ion batteries. We are working collaboratively to address questions about our testing and compliance with certification standards, and we will not hesitate to make changes that lead to improved testing processes and products."