is poised to start data-gathering flight tests of the 787 for the battery failure investigation, but certification and safety officials are indicating what the manufacturer and its customers have feared the most: It could be months and not weeks before the aircraft returns to service.
The gloomy prognosis is confirmed by U.S.Deborah Hersman, who says the board has “a lot of work to do” and is still “weeks away” from even pinning down the cause of the first battery fire, on a aircraft in Boston on Jan. 7. The NTSB investigation has pinpointed Cell 6 as the origin of the fire that broke out in the aircraft's eight-cell lithium-ion auxiliary power unit (APU) battery. Just prior to the event, the voltage “unexpectedly dropped from its full charge of 32 volts to about 28 volts,” says the board, which is consistent with the charge voltage of a single cell, Hersman notes.
“We know Cell 6 had multiple short circuits and got into a runaway condition and it propagated into other cells,” she says Hersman. The NTSB is “looking at the state of the cell charge, manufacturing processes and design of the battery. There are a lot of things we are looking at,” she adds. Next steps specifically outlined by the board include an evaluation of the validation methods originally used for certification of the battery as well as more testing of field replacement batteries.
“This investigation has demonstrated that a short circuit in a single cell can propagate to adjacent cells, resulting in smoke and fire,” says Hersman. As a result, “the assumptions used in the certification of the battery must be reconsidered.”
The parallel Japan Transport Safety Board (JTSB) investigation into the Jan. 16 mid-air main battery failure on an787 is moving on to the contactor and battery diode module maker in France, after in-depth analysis of the battery, the monitoring unit and charger were conducted in Japan and the U.S. The JTSB conducted CT scans of the main and APU batteries from the ANA aircraft at a facility as well as a scan of the main cells at the battery maker GS Yuasa in Kyoto.
Like the NTSB, the Japanese investigators report that a thermal runaway condition in which the cells are destroyed in a chain reaction was observed. It also says that adjacent Cells 3 and 6 were particularly damaged while all eight cells showed internal fusing. It also reports that the ground wire of the battery chassis was broken, though there is speculation this may have been caused by the action of the fire fighters responding to the incident.
The only glimmer of good news for Boeing is the's decision to approve the start of test flights to verify the vibration and temperature environment experienced by the batteries in the forward and aft electronic/electrical equipment bays. Clearance to take this first step toward ultimately testing and certifying a modified battery and monitoring system was signaled by the FAA on Feb. 7, the same day as an agency-approved one-off ferry flight of a newly painted 787 from Texas back to Everett.
However, as Boeing comes to grips with the harsh reality of the likely time it will take to recertify a revised battery system, it also faces a range of new questions. Beyond the uncertainty about how long the fix itself will take to develop, looming issues include the logistics of implementing the fix. Among the 50 grounded aircraft belonging to eight operators which, for example, will be modified first? Likewise, how will modifications be implemented on the growing fleet of undeliveredthat continue to stack up at Everett, Wash., where new 787s are rolling off the line at the rate of five per month?
Questions also remain over which of these takes priority and what follow-on disruption the modification program may cause to the already slowing process of change incorporation at the Everett Modification Center (EMC). The 100th 787 is on the assembly line, 50 have been delivered and the balance is made up of the original six development aircraft, 25 earlier production aircraft undergoing or awaiting modification in the EMC and more recently built aircraft awaiting delivery.
Watching events from across the Atlantic,CEO Fabrice Bregier says the company has been studying alternatives to the lithium-ion batteries it plans to use on the . According to Bregier, “nothing prevents us from going back to a classical plan that we have been studying in parallel.” Airbus has a different supplier, French battery specialist Saft, and the batteries are used for fewer functions than on the 787, thus they are less powerful. So far, Bregier sees no need to change the design and technology, though he says it would be possible to adjust the design of the current system while continuing to use lithium-ion-batteries. He expects no delay to the A350's planned entry into service. In case of a full battery replacement, Airbus would “have all the time we need to do this on the A350 before first delivery,” he says.
Bregier also reveals that Airbus redesigned the current battery system about a year ago because of safety concerns. The company declines to elaborate on exactly what change was made and what the alternative system would look like if it were to return to a more conventional solution.