NTSB press briefing on 787-short circuit came first, then fire
The National Transportation Safety Board held its second full media briefing on the investigation of the Boeing 787 battery fire Jan. 9 aboard a Japan Air Lines aircraft at Boston.
Deborah Hersman is chair of the NTSB. Following our usual format for live coverage, we’re synopsizing and paraphrasing her comments.
- General statement: Safety has been achieved through layers of redundancy and checks.
- Batteries on the 787 are unique to the 787. Have 8 cells of 4 volts each for 32 total volts.
- The event battery starts the APU. If it fails, APU won’t start and if it is running APU will shut down.
- Found thermal runaway, shorts.
- Trying to find original of fire and reviewing certification procedures.
- Have disassembled batteries. FDR shows voltage unexpectedly dropped from 32 volts to 28 volts. Consistent with discharge of a single cell.
- We believe evidence points to single cell initiating event.
- Cells 5-8 (left side of battery) shows greatest damage. Charred with temp exceeding 500F degrees.
- The body of evidence probably suggests event initiated in cell #6, with multiple signs of short-circuiting. Started thermal runaway spread to other cells and this started the fire.
- Now working to determine the cause of short circuiting in #6.
- Ruled out mechanical impact damage to the battery. All damage occurred after fire.
- Also ruled out external short-circuiting from battery. Damage occurred inside battery and after significant damage.
- Still considering: state of charge of each cell and method of delivery of charge; contamination; assembly damage; because battery is really a collection of eight batteries, looking at total design and assembly.
- Reviewing certification of battery design.
- Because 787 had novel designs and technology, existing regs didn’t encompass this. So FAA issued special conditions, including for the battery.
- Special interest to NTSB is how special conditions relate to batteries.
- We found Boeing determined failures could occur in the battery. Assessed likelihood of failure and affect of failures.
- Tests performed on batteries. Boeing indicated tests no evidence of cell-to-cell propagation. But our investigation shows that after short circuit, there is propagation and a fire.
- Boeing assessed that a smoke emission event would occur in less than one in every 10m flight hours. 787 has less than 100,000 flight hours with two battery events and smoke less than two weeks apart.
- This demonstrates a short circuit in a single cell can result in propagation and smoke events.
- NTSB still continuing with testing from batteries removed from 787s. Still reviewing certification and testing procedures.
- Sharing all information with FAA, EASA to get airplanes back into the air. Decision to return 787 to flight will be made by FAA.
- Will issue interim report within 30 days.
- Certification review by FAA initiated before grounding is a very serious event.
- The FAA conducts risk assessments for ferry flights and this was an airplane before delivery to a customer (referring to the Boeing ferry flight underway from Ft. Worth to Everett).
- There are nine special conditions for the battery the FAA issued, based on assumption of no smoke events in 10m hours. We know some assumptions were not met, much less a fire event.
- This was not unusual for Boeing to work with FAA on testing. It is not unusual for operator (Boeing) to conduct testing. Testing also done by Thales, others.
- We do have a long road ahead of us. Challenges. Fires consume evidence. But team has been able to identify failures, origin of event and how it cascades and have been able to rule things out.
- Interim factual report will be comprehensive factual report but no conclusions. Will have additional information. Important to get info out ASAP because the fleet is grounded.
- Haven’t ruled out other possible external contributors. Still looking at design, certification, manufacturing. Still a lot of work to do.
- Still working closely with Japanese counterparts. Their event occurred after our event. Our investigation has a little more time on these issues. Not yet in position to compare investigations.
- The NTSB is working very closely with Boeing, FAA, French and Japanese counterparts. If Boeing is proposing any changes, those will be made to FAA. We don’t determine if 787 returns to flight.
- We have pinpointed origin of the event to cell #6; had multiple short-circuits. It got into thermal runaway condition and propagated to other sees.
- We do know short-circuit came first. This does help us identify as we move forward what happened. Obviously certification is over all of these issues.
- We have not reached conclusions whether it’s OK to continue battery production. As part of investigation, GS Yuasa is part of our investigation.
- We don’t have information specifically where within Cell 6 the short circuit occurred.
- We have left a lot of issues on the table we’re looking at. We have not yet identified the cause of the short circuit. We are looking at the design, the manufacturing, the charging and how charging comes into the battery.