Ethiopian B787 fire was caused by battery short-circuit claim investigators

The British Air Accident Investigation Branch (AAIB)called for an improvement in certification requirements as a result of the fire which, it said, was probably the result of a botched electrical installation of the aircraft’s emergency locator transmitter (ELT) - the Honeywell Rescu 406AFN .
The investigation suggested that this had led to short-circuiting, causing its battery to overheat and start a process known as thermal runaway, which generates intense heat.
The fire spread in the aircraft’s rear upper fuselage while the aircraft was empty and unattended until the fire crews arrived, causing extensive damage to the 787’s composite materials hull.
In the report the AAIB said: “Significantly, the ELT battery wires were found…crossed and pinched together between the battery cover-plate and the ELT case…the cover plate was noticeably bulged in this location as the wires prevented it from sitting flush against the ELT case.
“The absence of any other aircraft systems in this area containing stored energy capable of initiating a fire, together with evidence from forensic examination of the ELT, led the investigation to conclude that the fire originated within the ELT battery.”
Honeywell has since changed its process to ensure that the wiring problem cannot be repeated
AAIB called on the the FAA to develop enhanced certification requirements for the use of lithium-metal batteries in aviation equipment, and to take account of current industry knowledge on the design, operational characteristics and failure modes of lithium-metal batteries.
The AAIB said inspections across the 787 fleet last year found tripped wires on 28 other ELTs, including one that had short-circuited in a way that did cause a thermal runaway event.