A Japan Airlines Boeing 787 suffered "severe fire damage" after a lithium-ion battery for the auxiliary power unit (APU) exploded on 7 January, the National Transportation Safety Board (NTSB) says.
The fire burned for 40min and damaged structure within a roughly 50.8cm (20in) radius of the battery in the 787's aft electrical equipment bay, the NTSB says.
Boston Logan Airport firefighters extinguished the fire near the APU battery box about 40min after being summoned by Japan Airlines maintenance and cleaning staff, who detected the fire, the NTSB says.
The NTSB has expanded its investigation of the incident that occurred shortly after the 787 landed and de-planed after a nearly 12h flight from Tokyo-Narita. Two more investigators, including senior air investigator David Helson, were dispatched to Boston, the NTSB says.
They will study the implications of the fire on the airworthiness of the aircraft and also how the fire and rescue crews responded.
The incident has again raised questions about the reliability and safety of the 787's unique electrical system, which replaces pneumatics and nickel-cadmium batteries as power sources for most of the on-board systems.
The 787 is not the first aircraft to introduce lithium ion batteries as a power supply, but it is the first to use it as a main battery and an APU battery.