US firm Honeywell has been asked to join the investigation into the fire on a Boeing 787 at Heathrow Airport amid reports of a probe into whether the plane's emergency transmitter played a role.
The transmitter sends a signal with the plane's location if it is involved in a crash.
The fire on a parked Ethiopian Airlines 787 on Friday brought back memories of two smouldering lithium-ion batteries in January that caused authorities to ground the 787 worldwide for more than three months. Boeing redesigned the systems that include those large, powerful batteries to win government approval so 787s could fly again.
Honeywell's emergency transmitter uses a lithium-manganese battery - a type of lithium-ion battery but with different chemistry that is considered more stable.
The UK's Air Accidents Investigation Branch said on Saturday that the most recent fire occurred well away from the lithium-ion batteries. Published reports said investigators were examining whether the transmitter could have caused or contributed to the fire.
A spokeswoman declined to say whether the focus had shifted to the emergency locater and warned against speculation on the causes of the incident.
Honeywell would not specify why authorities asked it to participate in the investigation.
"It's far too premature to speculate on the cause, or draw conclusions," spokesman Steve Brecken said. He directed other questions to the US National Transportation Safety Board, which is helping with the investigation.
Mr Brecken said Honeywell's emergency transmitters "have been certified by the FAA (Federal Aviation Administration) since 2005, are used on a number of aircraft models, and we've not seen nor experienced a single reported issue on this product line".