Boeing says the root cause of the 787 battery failures may never be established, but that it is moving ahead with a solution aimed at getting the aircraft back in the air.
The 787 fleet was grounded on 16 January following two incidents in which their lithium-ion batteries failed after overheating and leaking electrolyte, resulting in significant charring.
In the first incident, an auxiliary power unit battery on a Japan Airlines 787 failed while the aircraft was on the ground at Boston Logan International Airport, while in the second incident, an All Nippon Airways 787 had to be diverted to Takamatsu in Japan after the crew received a cockpit alert saying that the main battery had failed.
Boeing and battery manufacturer GS Yuasa have been working with the Japan Transport Safety Bureau and the US National Transportation Safety Board to investigate the battery incidents, but no definitive cause has been found for the battery faults so far.
"In the events of Logan and Takamatsu, we may never get to a single root cause, but the process we applied to understand the improvements that can be made is the most robust process that we have ever followed," says Boeing's vice-president and chief project engineer, Mike Sinnett.
Boeing has proposed significant changes to the battery system aimed at making it easier to cool the lithium-ion cells, as well as a new containment solution which would prevent overheated battery cells from starting a fire.
It has also reworked the battery charger with reduced maximum charging levels, a higher maximum discharging level and a softened charging sequence.
The US Federal Aviation Administration has approved a certification plan for the modified systems, which will undergo rigorous laboratory testing and a validation flight test before being certified for use on the global 787 fleet.