LONDON (AFP) - The British authorities probing a fire onboard a parked Boeing Dreamliner at London's Heathrow Airport recommended on Thursday that Honeywell distress beacons on all 787 planes be deactivated pending further checks.
The Air Accidents Investigation Branch (AAIB) also urged a review of the lithium-powered emergency locator transmitter (ELT) systems used in other aircraft types.
Detailed analysis of the transmitters, which help localise the plane if it crashes, "has shown some indications of disruption to the battery cells", it said in a report.
"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," it said.
Further investigations will be carried out into the blaze last Friday on an Ethiopian Airlines plane, which was empty at the time.
The incident is a blow to United States plane-maker Boeing, which withdrew from service its entire fleet of Dreamliners earlier this year due to separate concerns that lithium-ion batteries on board could cause fires.
A total of 68 Dreamliners have so far been delivered, and the AAIB recommended to the US aviation authorities that the transmitter systems in all of them be disabled.
"It is recommended that the Federal Aviation Administration initiate action for making inert the Honeywell International RESCU406AFN fixed emergency locator transmitter system in Boeing 787 aircraft until appropriate airworthiness actions can be completed," the report said.
It also recommended that the FAA and 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".
In a statement, Boeing said it supported both the AAIB's recommendations, "which we think are reasonable precautionary measures to take as the investigation proceeds".
"We are working proactively to support the regulatory authorities in taking appropriate action in response to these recommendations, in coordination with our customers, suppliers, and other commercial airplane manufacturers," it said.
"We are confident the 787 is safe and we stand behind its overall integrity."
The AAIB's report does not mean the Dreamliner fleet need be grounded again.
All planes carrying passengers in the US are required to have a distress beacon, and the devices are widely used around the globe.
But under US rules, operators can fly with inoperative transmitters for up to 90 days while they are being replaced or repaired. Similar regulations apply in Europe and other parts of the world.
The AAIB said Honeywell Aerospace has produced about 6,000 transmitters of the type found on the 787, and the Heathrow fire was the only incident of its kind.
The US based company, which sent experts to London following the blaze, said on Monday that they were never made aware "of any problem on this product", certified by the FAA since 2005.
Speaking shortly before the AAIB report was published, Honeywell spokesman Steve Brecken said it had not received any orders to temporarily disable the transmitters.
But "as a safety-first company, we would support an action like this as a precautionary measure if our team, or the AAIB and NTSB (US National Transportation Safety Board), determine it's necessary to do so", he told AFP.
The Dreamliner, which makes extensive use of lighter, carbon-based composite materials that reduce fuel consumption, came into service in September 2011.
Boeing issued a global grounding order in January after lithium-ion batteries overheated on two different jets.
The US aviation giant has not been able to identify the root cause of the problems, much to its embarrassment, but it said its modifications would prevent the problems recurring.
In April, an Ethiopian Airlines Dreamliner - reported to be the same plane that caught fire at Heathrow - flew from Addis Ababa to Nairobi on the first commercial flight since the grounding.
But the planes have been dogged by problems, with a string of flights worldwide cancelled or diverted due to mechanical issues.