The fire occurred on a parked Ethiopian Airlines plane Friday at London's Heathrow airport after the plane arrived there from Addis Ababa, Britain's Air Accidents Investigation Branch said in a statement Thursday. No one was on the plane at the time of the fire.
"The circumstances surrounding the occurrence did not fall within the definitions of an accident or serious incident," the statement said. "An investigation was commenced immediately and a team of AAIB Inspectors was deployed."
The investigation found that the fire started in the upper rear part of the aircraft, where the Emergency Locator Transmitter, made by Honeywell, is fitted.
"Detailed examination of the ELT has show some indications of disruption to the battery cells. It is not clear however whether the combustion in the area of the ELT was initiated by a release of energy within the batteries or by an external mechanism such as an electrical short," the statement said.
As the ceiling space where the ELT is located "do not typically carry the means of fire detection ... had this event occurred in flight it could pose a significant safety concern and raise challenges for the cabin crew in tackling the resulting fire."
"It is recommended that the Federal Aviation Administration, in association with other regulatory authorities, conduct a safety review of installations of Lithium-powered Emergency Locator Transmitter systems in other aircraft types and, where appropriate, initiate airworthiness action," the statement said.