|Damaged electrode with sign of internal short circuit from the 787 Li-ion battery. Source: NTSB. Click to enlarge.|
At a briefing on the progress in the investigation of the Li-ion battery fire on-board a JAL Boeing 787 at Logan Airpot in Boston (earlier post), NTSB Chairman Deborah Hersman reported that the investigating team had found signs of electrical short circuiting and thermal runaway in the cells. The NTSB is working to determine the cause.
The next steps in what appears will be a lengthy investigation will be to complete the in-house laboratory examinations; conduct examinations and testing of exemplar batteries; and to synthesize lab examination findings with fire forensics and aviation systems investigation.
|Example of a cell CT scan. Source: NTSB. Click to enlarge.||CT scan of Cell 6. Source: NTSB. Click to enlarge.|
So far, NTSB has performed an exam and teardown of the JAL battery at its Materials Laboratory. Boeing and its various suppliers have also performed component exam and teardowns:
- Securaplane Technologies, Battery Charger Unit and Start Power Unit
- United Technology Aerospace Systems, APU Controller
- Boeing, Two General Purpose Modules
- Kanto Aircraft Instrument, Battery Monitoring Unit
The battery itself comprises 8 GS Yuasa prismatic Li-ion cells each with a nominal capacity of 75 Ah, with a nominal voltage of 3.7 V. So far, NTSB has performed:
- CT scan of the entire assembly.
- Cell 1: CT scan
- Cell 2: disassembly
- Cell 3: CT scan
- Cell 4: CT scan
- Cell 5: CT scan, disassembly, scanning electron microscopy, energy dispersive electroscopy
- Cell 6: CT scan, disassembly
- Cell 7: CT scan, disassembly, SEM
- Cell 8: disassembly
|Source: NTSB. Click to enlarge.|
Boeing issued a statement after the update, welcoming the progress.
In order to ensure the integrity of the process and in adherence to international protocols that govern safety investigations, we are not permitted to comment directly on the ongoing investigations. Boeing is eager to see both investigative groups continue their work and determine the cause of these events, and we support their thorough resolution.—Boeing statement