Boeing has developed a comprehensive set of improvements to the 787 lithium-ion batteries that add several new layers of safety and reliability to the design. These improvements are undergoing extensive certification testing. Once testing is complete and the U.S. Federal Aviation Administration (FAA) and other international regulators grant their final approval, operators will be able to safely resume commercial flights of their 787s.
“We will be positioned to help our customers implement these changes and begin the process of getting their 787s back in the air,” said Boeing Commercial Airplanes President and CEO Ray Conner. “Passengers can be assured that we have completed a thorough review of the battery system and made numerous improvements that we believe will make it a safer, more reliable battery system.”
Improvements include enhanced production and operating processes, improved battery design features and a new sealed battery enclosure.
Battery system enhancements address possible causes of battery failure identified by the Boeing technical team. The technical team’s findings were verified by an independent group of lithium-ion battery experts from industries, universities and national laboratories.
Boeing teamed with Thales, the provider of the integrated power conversion system, and battery maker GS Yuasa to develop and institute enhanced production standards and tests to further reduce any variation in the production of the individual cells as well as the overall battery.
Four new or revised tests have been added to screen cell production, which now includes 10 distinct tests . The batteries have eight cells, each of which will now go through more rigorous testing in the month following its manufacture. This will include a 14-day test during which readings of discharge rates are being taken every hour. The new design, processes and test will ensure that every battery cell meets the highest quality and reliability standards.
To further improve reliability, Boeing, Thales and GS Yuasa will lower the highest charge allowed in the battery monitoring unit and charger and raise the lower level allowed for discharge. The battery charger will also be adapted to soften the charging cycle to put less stress on the battery during charging.
Inside the battery charger, each cell will be better insulated. An electrical insulator is being wrapped around each battery cell to electrically isolate cells from each other and from the battery case, even in the event of a failure. Electrical and thermal insulation installed above, below and between the cells will help keep the heat from the cells from affecting one another. This helps isolate it from the rest of the battery in the unlikely event that a cell fails.
The wire sleeving and the wiring inside the battery will be more resistant to heat and chafing, and the metallic bars that connect the eight cells of the battery will be attached with new fasteners that include a locking mechanism.
Small holes at the bottom of the battery case will allow moisture to drain away from the battery. Larger holes on the sides of the battery will allow a failed battery to vent with less effect on other parts of the battery.
Lastly, the battery will now be enclosed in sealed stainless steel. The enclosure isolates the battery from the rest of the equipment in the electronic equipment bays. It ensures that there can be no fire inside the enclosure, thus adding another layer of protection to the battery system. Any fumes or heat that builds up in the enclosure will be vented outside the airplane. Testing to gain FAA approval of the battery enhancements has already started, with the FAA’s permission.
New Design Ensures Airplane Safety
Before certification testing, during engineering testing, the team demonstrated that the new housing could safely contain the failure of all eight battery cells. The “ultimate” load is the equivalent of 1.5 times the maximum force ever expected to be encountered during a battery failure. The housing easily withstood this load and did not fail until pressure was at more than three times the ultimate load. In another test, the team demonstrated that fire cannot occur within the new enclosure. This means that even in the rare situation a battery does fail, the airplane can continue on safely to its scheduled destination.
“We are following all of the necessary protocols to get our new design fully approved and properly installed so that we can help our customers start flying as soon as possible. We’re simultaneously moving out on an effort to resume deliveries but completing our certification work, and getting the delivered fleet flying again is our first priority,” said Conner. “Our customers and their passengers have been incredibly patient as we have worked through this process, and we thank them very sincerely for their continued support and confidence in the 787.”
Boeing Press Release