The US National Transportation Safety Board (NTSB) has raised a number of concerns with the manufacturing and inspection processes followed by GS Yuasa, the Japan-based company that makes the Boeing 787’s lithium-ion batteries.
The board raises its concerns in a report, released today, about the 7 January 2013 battery fire on a Japan Airlines (JAL) Boeing 787 at Boston. One of the aircraft’s lithium-ion batteries caught fire, prompting a three-month grounding by the US Federal Aviation Administration (FAA) of the type.
Though the report says the fire resulted from a general lack of oversight in the design by the FAA and Boeing, it highlights a number of concerns with GS Yuasa.
Those include the manual process GS Yuasa employees use to hand-flatten electrode “windings”, which the NTSB says can create wrinkles in the electrodes.
Those defects, which could lead to short circuiting, are similar to wrinkles found on other 787 batteries, including the battery that caught fire on the JAL aircraft in Boston.
The board also notes that GS Yuasa performs welding, which generates airborne debris, in the same area where it assembles internal cell components.
The debris, which can include small metallic particles, can land on sensitive internal components, says the board.
In addition, NTSB investigators discovered that computed tomography equipment used by the company was not set to a resolution that could identify cell defects, such as wrinkles, folds and creases.
Though GS Yuasa has reported that its inspection processes have resulted in less than 1% of its cells being rejected, the board says the low reject rate may result from inadequate inspections.
“This low rejection rate could be the result of few defects to detect; however, most of the evidence… indicated that GS Yuasa’s inspection process did not adequately screen for defects that developed during the manufacturing process,” says the NTSB.
The report also reveals a lack of oversight by Boeing, which the NTSB says performed no audits of GS Yuasa prior to the 7 January 2013 fire.
Instead, Boeing relied on Thales, the prime battery contractor, to oversee Yuasa.
After the incident, however, Boeing discovered 17 instances in which GS Yuasa or Thales Group, the prime contract, did not conform with its requirements.
Those include failures by GS Yuasa to adhere to written procedures and to properly communicate to Boeing and Thales about proposed battery testing changes, says the NTSB.
Boeing flagged Thales for improper adherence to contract requirements related to procedural changes.
The FAA, which also did not audit GS Yuasa prior to the Boston fire, audited the company in late January 2013.
It found that GS Yuasa failed to properly follow battery component assembly and installation instructions and did not comply with requirements for marking parts, the NTSB says.