Safety Board Releases Details of Boeing Battery Fire: WSJ

United States air-safety investigators documented the extensive damage and broken components found inside a Boeing Co. 787 battery after it erupted in flames two months ago, but their report didn't resolve the central mystery of precisely what caused the blaze.

The National Transportation Safety Board's update Thursday provided some new details about how a short-circuit that began in a single cell spread to seven other cells and ended up in a uncontrollable thermal reaction that quickly reached about 500 degrees Fahrenheit, burning through the battery's metal container. The January fire occurred on a Japan Airlines Co. 787 Dreamliner parked at a gate in Boston, without any passengers.

The 38-page report also indicated that investigators basically determined that various electronic components connected to the battery—ranging from a charging unit to a sophisticated surge protector—were intact and didn't exhibit any failures or defects. Tests after the fire showed those components generally worked as expected, according to the report.

The findings are likely to focus more public attention on whether some type of internal battery defect of problem could have prompted the sequence of events that led to the fire. But as it has in the past, the safety board stopped short of indicating whether an external or internal cause was responsible.

The fire and smoke from the event were so intense that firefighters couldn't see even a few inches in front of themselves when they entered the electronics bay containing the burning battery, the report said. A fire captain on the scene told investigators that the battery was "hissing loudly and liquid was flowing down the sides of the battery case" before it "exploded."

As expected, much of the report was devoted to an examination of the Federal Aviation Administration's procedures and its oversight of Boeing tests used to certify the safety of the 787's batteries. The safety board previously challenged the validity of the engineering assumptions and risk analyses the FAA and the Chicago plane maker initially relied on to demonstrate the safety of the batteries manufactured by Japan's GS Yuasa Corp.

Before certification of the 787, Boeing's hazard assessment deemed that a battery fire would be a "catastrophic" event that could cause the loss of an aircraft, according to the report. But the company determined that overcharging was the "only known failure mode" that could result in such an outcome.

The NTSB previously determine that the Japan Airlines battery wasn't overcharged before it caught fire.

In conjunction with the FAA, Boeing years ago determined that redundant safety systems, many of which would be installed specifically to prevent battery overcharging, meant the likelihood of a battery fire was "extremely improbable." Before the FAA approved the plane to carry passengers, the agency agreed with Boeing's conclusion that the chance of a 787 lithium-ion battery fire was less than one in a billion flight hours, Thursday's report said.

The report also said that all of the tests initially to determine the safety of the 787's battery system were conducted by Boeing or its subcontractors and were reviewed by Boeing engineers, along with company employees designated to serve as the FAA's representatives.

The FAA previously said it approved the type of testing that was done, helped determine standards for passing those tests and was kept informed about Boeing's risk assessments.

Before the world-wide fleet of Dreamliners was grounded, the planes had flown in service for about 50,000 flight hours and two of them experienced burning batteries. The second plane to experience a batter incident was a 787 operated by All Nippon Airways Co. that made an emergency landing on a flight in Japan on January 17.

Investigators continue to review manufacturing and quality-control issues related to the batteries, Thursday's report said. The safety board, among other priorities, is paying "particular attention to the coordination of responsibility and authority of the contractors and subcontractors" that worked on the plane's battery system.

With the 787's grounding, resulting in international investigations and recertification efforts under way simultaneously, NTSB Chairman Deborah Hersman said "it is essential to provide the aviation community, policy makers and the public with the factual information we are developing,"

Along with the report, Mr. Hersman announced that the board will convene a pair of public sessions next month to delve deeper into lithium-ion issues. A forum in mid-April is intended to concentrate on lithium-ion battery technology and transportation safety, while a later hearing will focus on the design and FAA approval of the 787's battery system.