The Air Accidents Investigation Branch also recommended that the U.S. Federal Aviation Administration and other regulators carry out a safety review of lithium-battery powered emergency locator transmitter systems in other types of aircraft.
In a report issued Thursday, the investigators said that the greatest damage to the parked Ethiopian Airlines Dreamliner occurred around the aircraft's Rescu406AFN emergency locator transmitter near the plane's tail.
Investigators said it was not clear if the fire was caused by the transmitter's lithium-manganese dioxide batteries or a short near or around the transmitter, but recommended that the FAA switch off the Honeywell transmitter in all Boeing 787s "until appropriate airworthiness actions" can be carried out.
A spokeswoman for the investigation branch said the easiest way to make the transmitter systems "inert" — as set out in their recommendations — would be to take out their batteries.
The FAA didn't immediately say whether it will follow the recommendations. A spokesman said the agency will have a response later Thursday.
Boeing said it supports the recommendations — which it called "reasonable precautionary measures" — and was working with regulators to take appropriate action in response.
Honeywell said "Temporarily addressing the (transmitters) on Boeing 787s as a precautionary measure is prudent." Honeywell said it doesn't expect any noteworthy financial impact as a result.
U.K. investigators acknowledged that this model of Honeywell transmitter is installed in a wide range of planes, and previously had experienced no similar issues.
However, the investigators noted that large passenger planes don't usually have fire detection or suppression gear in the space above cabin ceilings, "and 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," the report said.
Boeing spokesman Marc Birtel noted that the transmitter isn't required by U.S. federal aviation laws, but is required by some foreign regulators for their airlines or their airspace.
Birtel said the transmitter, which helps with search and rescue operations, takes about an hour to remove from a 787.
When news of the Ethiopian Airlines' blaze at first broke last week, investors in Boeing were worried that the lithium ion battery problem that had grounded the whole 787 fleet in January for almost four months had not been fixed. However, the AAIB said early on there was no evidence that was the case in the Heathrow incident.
"We are confident the 787 is safe and we stand behind its overall integrity," Boeing said on Thursday.
Boeing Co. shares rose $1.83, or 1.8 per cent, to $106.62 in afternoon trading on Wall Street. Honeywell International Inc. shares rose 38 cents to $82.82.
Freed reported from Minneapolis. AP Business Writer Sarah Skidmore in Portland, Ore. contributed to this report.