UK investigators have found no immediate connection between the heat damage on an Ethiopian Airlines Boeing 787-8 and the aircraft's batteries.
The aircraft sustained "extensive heat damage" in the upper aft fuselage, as well as smoke throughout the fuselage, says the Air Accidents Investigation Branch.
But it points out that the main and auxiliary power unit batteries - located in the forward fuselage and just behind the wing - are "remote" from the area of heat damage.
The aircraft (ET-AOP) was parked at a stand adjacent to a fire station at London Heathrow when the incident occurred at 16:50 on 12 July.
The AAIB has yet to determine the source of the damage, and has not used the term "fire" - it simply says the aircraft "suffered an event".
It adds that the aircraft is being examined in a hangar at the airport. The affected upper rear fuselage area is "complex", the AAIB says, and the initial investigation will probably take several days.