New Report on the Boeing 787 Dreamliner Battery Problems of 2013

I wrote (March 14, 2013) about the two battery incidents that occurred on the new Boeing 787 aircraft in early 2013 and noted that there was a lot of focus on fixes and not enough on causes of the problem.

At the time, the only cause identified was a short circuit in a cell.  There were some battery production process changes made as well as these design changes:

Boeing modified the 787 battery design and its installation configuration to include (1) additional insulation between the battery cells, (2) vents in the side of the battery case, (3) a stainless steel enclosure for the battery case, and (4) an ECS duct that vents from the interior of the stainless steel enclosure to the exterior of the airplane to prevent smoke from entering the occupiable space of the airplane.

On November 21 2014 the NTSB released an update to the original report:

The report notes the original two incidents, and an additional third incident in January 2014:

On January 14, 2014, an LVP65-8-403 main battery failed on a JAL 787 airplane that
was parked at a gate at NRT. (The airplane was being prepared for scheduled flight.) The Japan Civil Aviation Bureau is investigating this incident with assistance from the JTSB and the NTSB. Maintenance personnel reported seeing smoke outside the cockpit window. Preliminary information indicated that one cell had overheated and vented electrolyte and that the enclosure for the battery case contained the vented electrolyte.

The report is there to read.  Some of my takeaways are:

• For complex assemblies where there are areas of the assembly hidden from observation it is important to do teardown inspections and/or x-ray inspections to look for problems.
• A higher lever corollary to the teardown/x-ray comment above: when launching a new product, do your inspections as though you were doing a problem investigation. In other words, instead of simply confirming your components are "to print", your process is running according to the control plan, that end of line tests (EOL) are passed, and the assembly is to print; dig in and search for anomalies, differences between parts, and internal damage. With the battery, the NTSB really lifted the skirt and probed deep into the battery cells.  
• I am reminded that designs are surprisingly robust and EOL tests are surprisingly weak. Part variation and defects still allow the assembly to work, for a time.  EOL tests fail to catch deviations. Within the battery cells the investigation