Engineering news
Boeing has released details of the fix for the lithium-ion batteries on board its grounded 787 aircraft and reassured customers that commercial flights would resume "within weeks, not months."
The aerospace firm said it had come up with 80 possible causes for the battery problems and although they had not pinpointed the exact causes, the battery had been redesigned and already completed a third of the required safety tests.
Boeing chief project engineer Michael Sinnett said the new battery design had many layers of safeguards to prevent battery fires and overheating. It also has measures to contain the problem from spreading and to keep the aircraft safe, even if the batteries malfunction again, he said.
The batteries will undergo four additional tests in the month following their manufacture in Japan, including a two-week test during which readings of discharge rates will be taken every hour. Once installed and operating, the batteries will reach a lower maximum charge level and a higher discharge level with the use of a redesigned monitoring unit and charger.
An electrical insulator is being wrapped around each battery cell to electrically isolate cells from each other and from the battery case. Electrical and thermal insulation is being installed above, below and between the cells to help keep the heat of the cells from accumulating.
Wire sleeving and the wiring inside the battery will be upgraded to be more resistant to heat and chafing. New fasteners will attach the metallic bars that connect the eight cells of the battery. These fasteners include a locking mechanism.
The battery case has had holes added at the bottom to allow moisture to drain away from the battery and larger holes on the sides will allow a failed battery to vent. The redesigned enclosure is made of stainless steel to isolate the battery from the rest of the equipment in the electronic equipment bays. It also will ensure there can be no fire inside the enclosure.
Sinnett said: “Our first lines of improvements, the manufacturing tests and operations improvements, significantly reduce the likelihood of a battery failure. The second line of improvements, changes to the battery, helps stop an event and minimize the effect of a failure within the battery if it does occur. And the third line of improvements, the addition of the new enclosure, isolates the battery so that even if all the cells vent, there is no fire in the enclosure and there is no significant impact to the airplane.”
The 787 fleet was grounded worldwide by the US Federal Aviation Administration (FAA), its counterparts in Japan and other nations in January, following a battery fire in a Dreamliner parked in Boston and an overheated battery that led to an emergency landing of another 787 in Japan. About half the 787 jets in use were with Japanese carriers.
The new batteries are in production and could be installed within the next few weeks. New enclosures for 787 batteries also are being built and will be installed in airplanes in the weeks ahead.
Boeing did not rule out further delays to ensure safety and said they were in close contact with the US government authority. Earlier this week the FAA approved Boeing's safety certification plan.
“It's a safe airplane. We have no concerns at all about that,” Sinnett said.