This was no small fire. It seems to have burned through the hull; the image shows the ribs. No public explanation for the fire has been given yet, but we know from reports that it does not appear to have anything to do with the main batteries. The investigation is being led by the UK’s Air Accident Investigation Branch (AAIB).
The 787 is a complex airplane in electrical terms, as this Boeing chart illustrates. Moreover, it is not commonly known that the 787 uses 30% more power than then much larger A380. The 787 is truly an “all-electric” airplane.
According to the WSJ, there are several electrical parts that are located near the fire location including two remote power-distribution units and three remote data concentrators. In the same article, the vendors for these parts, GE and UTX, were quoted saying that neither had been contacted by the AAIB regarding the fire investigation.
At present it appears, from reports, that an area of focus will be the galley below the burnt area. According to Seatguru.com, the layout of the Ethiopian 787 looks like this. As one can see, the back of the cabin, where the burnt area exists, is above the rear galley.
But, at this stage, the galley can be only one area of attention for the AAIB. The investigation process is going to be deliberate and painstaking. The 787 is going to get more attention than any other airplane because of its record. The investigation may show the 787 has more issues with its electrical systems.
Once the cause is identified the repair phase will start. Boeing has a well-established process to fix the 787 from damage, like “ramp rash”. This fire damage is not quite the same. It is unclear at this stage how much damage there is below the skin – the damage may be more extensive than can be seen. The fire could have been burning for a while before the smoke was seen and the fire extinguished. As intriguing as the cause of this fire has been, so will be the repair process.