Boeing today outlined its plans for preventing the 787 Dreamliner's batteries from overheating or igniting, issues that have kept the aircraft's global fleet grounded for nearly two months.
While noting that it had not identified the root cause of the heat issues, the aircraft maker said during a news conference Friday in Tokyo that it had developed additional safety features designed to prevent heat issues with the planes' lithium-ion batteries.
"We've come up with a comprehensive set of solutions that result in a safer battery system," Boeing Chief Project Engineer Mike Stinnett said in a statement. "We have found a number of ways to improve the battery system and we don't let safety improvements go once they are identified."
The Federal Aviation Administration ordered airlines to ground their fleets of the much-hyped Dreamliner in January after an issue with the aircraft's lithium-ion batteries forced the evacuation of an All Nippon Airways flight. A similar incident occurred January 7 when a Japan Air Lines 787 on the ground at Boston's Logan International Airport caught fire.
The batteries will be wrapped in new thermal and electrical insulation materials to prevent heat from one cell from spreading to others. The battery will then be encased in a stainless steel enclosure to isolate it from other electrical equipment. Another modification involves the addition of drain holes to the battery enclosure to allow any moisture to drain away from the battery.
Boeing also said that it will narrow the acceptable level of charge for the battery, and the battery charger will be adapted to soften the charging cycle to put less stress on the battery during charging.
The plan, which won the FAA's approval earlier this week, also involves modified production and operating processes.
Some other details from Boeing's work to date:
During engineering testing, which occurs prior to certification testing, the team demonstrated that the new housing could safely contain a battery failure that included the failure of all eight cells within the battery. 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 pressure and did not fail until the pressure was more than three times the ultimate load.
Through another test, the team demonstrated that fire cannot occur within the new enclosure. Its design eliminates oxygen, making the containment unit self-inerting. Inerting is a step above fire detection and extinguishing as it prevents a fire from ever occurring. The design also vents all vapors by venting directly outside of the airplane rather than into the equipment bay.
During the briefing, Stinnett suggested that reports of fires were overblown and that the battery incidents never posed a threat to aircraft. The problem, he said, was "limited to the function of the battery in the immediate area of the battery, but the airplane was not at risk," according to an account published by The Verge.
"In the factual report you can see that the only report of flame was two small three-inch flames on the front of the battery box on the connector," he said. "There were no flames inside the battery and in the Takamastu event there was no fire at all."
Boeing hopes the new measures will help get its flagship aircraft back in the skies. So far, 50 planes have been delivered to airlines around the world.
"As soon as our testing is complete and we obtain regulatory approvals, we will be positioned to help our customers implement these changes and begin the process of getting their 787s back in the air," Boeing CEO Ray Conner said in a statement. "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."
With the FAA's permission, the Chicago-based aircraft builder began conducting test flights of the Dreamliner early last month to determine the cause of the battery issues. Meanwhile, the National Transportation Safety Board said it had traced the JAL battery fire to short circuit of a single cell that then spread to other cells.
After a long history of delays and production problems, the much-hyped Dreamliner -- a plane that features innovative use of composite materials -- was finally released to its first customer in September 2011, some three years behind schedule. The Dreamliner testing program was temporarily halted in November 2010 after an onboard electrical fire.