Boeing faces calls to re-design lithium-ion batteries
The JCAB’s call for a second battery redesign goes beyond the recommendations from two previous investigations about the 2013 battery incidents by the Japan Transportation Safety Board (JTSB) and the US National Transportation Safety Board (NTSB). The JCAB’s latest report calls for more action from Boeing.
Lithium ion batteries used on board 787s have been shown to be responsible for three reported cell venting events since January 2013.
The JCAB is calling for the battery redesign despite finding that two of the three protective layers from a May 2013 battery redesign worked as intended, and the safety of the aircraft was never at risk during the incident on 14 January 2014.
The JCAB report said: “Considering the fact that one cell was overheated/damaged during this event following the Boston and Takamatsu events,it is considered that, for keeping peace of mind for the passengers and the public people [sic] on the safety of B787 fleet, further improvements of the reliability for cells and battery system are necessary”.
The JCAB is requesting that Boeing assess all of the potential causes identified in three 787 incidenets and then “accelerate” making possible design changes, followed by an “early” certification process.
The 787 aircraft uses two lithium ion batteries made by Japan-based GS Yuasa. Both batteries are comprise eight cells delivering 32 V nominally.
Boeing’s battery design differs from the lithium ion batteries installed in the company’s European rival Airbus A350-900. The Airbus battery supplier, Saft, designed a system featuring four batteries, each composed of 14 cells delivering 25 V nominally combined. As a result the A350-900 uses more batteries that demand less power from each cell compares with Boeing’s 787 system.
The first two battery failures on the 787 posed serious safety issues. In both incidents, a single overheating cell vented, causing adjacent cells in the tightly packed battery box to fail and partly melt their aluminium enclosure. Indeed all three of the major investigations into the 787 battery failures have discovered that an internal short circuit occurred within a cell. The investigation reports propose several possible causes such as cold soaking, the formation of dendrites and manufacturing errors.
In response to the initial investigations, Boeing has redesigned how the batteries were installed with more spacing and thermal shielding added between each cell. The eight-cell pack was also enclosed in a stainless steel case.
The JCAB report indicates that two of the three layers of protection, which were designed to prevent a thermal runaway within the battery and minimize damage, worked as Boeing planned. However the JCAB investigators found that in the third cell venting incident the first layer of protection, which was implemented to prevent a cell from overheating in the first place, had failed.
Related articels and links:
www.mlit.go.jp/common/001064275.pdf
News articles:
Lithium battery shortcomings led to Boeing 787 fire
Trial by fire: Boeing should have chosen a safer type of Lithium-ion battery chemistry for its 787
FAA review addresses Boeing 787 Dreamliner safety fears
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
