At the time of going to press, the 787 fleet has now been grounded for six weeks without a definitive solution in sight to solve the perceived problems with the lithium-ion battery installed on the aircraft type. Boeing and investigators from the US National Transportation Safety Board (NTSB) as well as Japanese investigators have all conducted exhaustive examinations of the lithium-ion battery from the Japan Airlines 787, which caused a fire on the aircraft when it was parked at Boston Logan airport. The latest update from the NTSB on February 7 has determined that the majority of evidence from the flight data recorder and both thermal and mechanical damage pointed to an initiating event in a single cell in the battery, which is comprised of eight individual cells. The NTSB state that cell showed multiple signs of short circuiting, leading to a thermal runaway condition, which then cascaded to other cells.
As investigators work to find the cause of the initiating short circuit, they ruled out both mechanical impact damage to the battery and external short circuiting. It was determined that signs of deformation and electrical arcing on the battery case occurred as a result of the battery malfunction and were not related to its cause.
NTSB Chairman Deborah Hersman said that potential causes of the initiating short circuit currently being evaluated include battery charging, the design and construction of the battery, and the possibility of defects introduced during the manufacturing process.
During the 787 certification process, Boeing studied possible failures that could occur within the battery. Those assessments included the likelihood of particular types of failures occurring, as well as the effects they could have on the battery. In tests to validate these assessments, Boeing found no evidence of cell-to-cell propagation or fire, both of which occurred in the JAL event.
The NTSB learned that as part of the risk assessment Boeing conducted during the certification process, it determined that the likelihood of a smoke emission event from a 787 battery would occur less than once in every 10 million flight hours. Noting that there have been two critical battery events on the 787 fleet with fewer than 100,000 flight hours, Hersman said that "the failure rate was higher than predicted as part of the certification process and the possibility that a short circuit in a single cell could propagate to adjacent cells and result in smoke and fire must be reconsidered".
The investigation will continue and will include testing on some of the batteries that had been replaced after being in service in the 787 fleet.
"The decision to return the fleet to flight will be made by the FAA, which underscores the importance of cooperation and coordination between our agencies," Hersman said.
Meanwhile, the Japan Transport Safety Board (JTSB) has found incorrect wiring to how All Nippon Airways (ANA) 787’s main battery and its auxiliary power unit battery were connected. Although it is unlikely the incorrect wiring caused the overheating of the ANA 787’s main battery, investigators say that it warranted further investigation. Japanese investigators also found a slight swelling in ANA 787 aircraft’s auxiliary power unit (APU) battery but it has not been determined whether the swelling is problematic or normal.
As the investigation continues, 787 operators have rescheduled their network to account for the 787 being grounded until the end of May. The grounding of the fleet is generating substantial losses for these airlines – LOT Polish Airlines has estimated that the grounding of its two 787 aircraft costs $50,000 a day without taking into account the cost of passenger complaints and some other costs.
787 battery investigations continue
