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NTSB: No root cause found in Boeing Dreamliner 787 battery fire

Updated: March 7, 2013 4:35PM

A lithium-ion battery fire that occurred onboard a Boeing Dreamliner 787 airplane in Boston, contributing to the grounding of the full fleet of planes in January, was not easy to put out, taking an hour and 40 minutes before the event was described as “controlled.”

That’s according to an interim report released Thursday by the National Transportation Safety Board right before the agency announced it will hold a hearing and forum in mid-April to provide additional information to advance its investigation of the fire.

The board is still looking for the cause of the fire, which occurred onboard a Japan Airlines 787 while it was on the ground.

The NTSB interim factual report said that during the fire, aircraft rescue and fire fighting personnel repeatedly applied Halotran, a fire extinguishing agent to put it out. A fire captain said the battery was emitting white smoke, creating heavy smoke conditions and the battery was hissing loudly. The fire captain said he received a burn on his neck when the battery in his words “exploded.” Because of the heavy smoke firefighters had to use a thermal imaging camera.

The report said the 787’s avionics cooling function is designed to exhaust smoke overboard through fans in cooling ducts and changing supply valve positions, but that didn’t happen. That’s because during the incident, the electrically-driven supply valves couldn’t function because an Auxiliary Power Unit lost power after the fire started.

Federal Aviation Administration officials, who grounded the planes, are expected to make a decision in the next few days on whether to approve a plan by Boeing to revamp the 787’s lithium-ion batteries to prevent or contain future fire.

Chicago-based Boeing Co. has said it is ready to move quickly to get its 787s fixed and back in the air if it gets federal approval for its proposed fix to the battery problem. It submitted a plan to the FAA on Feb. 22.

The 787 Dreamliner is the first plane to use rechargeable lithium-ion batteries for its main electrical system. Such batteries are prone to overheating and have safeguards that were designed to prevent fires and contain a fire should one occur.

Reuters earlier reported that Boeing has proposed modifications to the design of the lithium-ion batteries and new systems to contain flammable materials after smoke or fire incidents on two aircraft in January. These measures include a stronger, stainless steel battery containment box and a tube to vent fumes and heat outside the airplane, should a fire occur in flight, Reuters has said.

All 50 of the Dreamliner jets in service around the world have been grounded since a lithium-ion battery in a 787 operated by Al Nippon Airways overheated Jan. 16, forcing an emergency landing in western Japan, following the Japan Airlines incident.

Investigators have said the batteries experienced short-circuiting and thermal runaway, a chemical reaction that causes progressively hotter temperatures.

Regarding the upcoming hearing, NTSB Chairman Deborah Hersman said,

“With the grounding of the 787 fleet, concurrent international incident investigations, redesign and re-certification activities taking place simultaneously, it is essential to provide the aviation community, policy makers and the public with the factual information we are developing.

“The information developed though the upcoming forum and the hearing will help the NTSB and the entire transportation community better understand the risks and benefits associated with lithium batteries and illuminate how manufacturers and regulators evaluate the safety of new technology.”

The boards interim report did not include any analysis.

It said records from Boeing showed that the Auxiliary Power Unit battery was disconnected but not removed from the airplane on Dec. 5, 2012, as a precaution while an electrical power panel was inspected for foreign object damage. The battery was reconnected the next day.

The report also detailed hazard assessment steps Boeing initially performed to land approval to use lithium-ion batteries on the new technologically advanced plane. The report stated Boeing identified two hazards associated with the main and APU lithium-ion battery: that the battery would vent smoke with fire, classified as catastrophic, and that the battery would vent and/or smoke without fire, which was classified as hazardous. It stated Boeing determined that overcharging was the only known battery failure mode that could result in battery cell venting with fire and determined that cell venting without fire could be initiated by several different failures including external overheating, external and internal short circuiting, recharging a battery that has been overdischarged among others.

To evaluate the effect of cell venting resulting from an internal short circuit the report said Boeing performed testing that involved puncturing a cell with a nail. That resulted in cell venting with smoke but no fire. Boeing also acquired information from other companies about their experience using similar lithium-ion battery cells, the report said. The results of the assessment and analysis were used by Boeing to incorporate safety features inside and outside the battery.

The NTSB previously reported that Boeing had determined the probability that a battery could vent smoke was one in every 10 million flight hours, but as of Jan. 16, the in-service 787 fleet had accumulated less than 52,000 flight hours and two events of smoke emissions from a 787 battery had been reported.

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