Ms Hersman said they were now following up two lines of inquiry - the actual cause of the short circuit, and why the certification process failed to pick up the defect in the battery's design.

BBC: Boeing 787 Dreamliner tests 'missed fire risk'

But several other possibilities are being explored, including contamination or defect during manufacturing, flaws in the design or construction of the battery, and problems with battery charging.

CNN: Boeing can conduct Dreamliner test flights