Investigators say crew would have struggled to contain blaze once plane was in mid-air

The fire on board a Boeing 787 Dreamliner at Heathrow last week started in a component carrying lithium batteries, investigators have said, in a blaze that crew would have struggled to contain mid-flight.

Early findings show that the fire, which burned through the fuselage of the plane and filled the cabin with acrid smoke, could not have been easily extinguished, or quickly detected while the plane was airborne.

Britain's Air Accident Investigations Branch (AAIB) has urged American aviation authorities to ensure that the component, an emergency locator transmitter powered by lithium-manganese dioxide batteries, be removed or disconnected.

The transmitter is a homing beacon used in emergencies to locate a missing plane, and removing the part should not affect the Dreamliner. There was no suggestion from the AAIB that the plane should again be taken out of service.

While the batteries are of a slightly different type to those powering Boeing's plane, the findings may further undermine confidence in the 787's pioneering technology. The findings will have implications for other planes as the part, supplied by Honeywell, is fitted in around 6,000 aircraft. The AAIB has recommended a safety review of the lithium-powered transmitters in all planes.

Boeing said: "As a party to the investigation, Boeing supports the two recommendations from the AAIB, 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 co-ordination with our customers, suppliers, and other commercial airplane manufacturers.

"We are confident the 787 is safe and we stand behind its overall integrity."

Emergency services including fire crews with water hoses were needed to put out the fire on the Ethiopian Airlines plane, which was parked at a remote stand at Heathrow.

David Learmount, safety editor at Flight Global, said: "Cabin crew do not have that sort of thing at their disposal. The possibilities are awful. If that had spread the aircraft's structural integrity and systems would have been at severe risk and the cabin would have been full of smoke. It's a potential nightmare scenario."

The Boeing 787 went into service in late 2011, after years of production delays. Airlines have queued up to buy the pioneering "plastic plane", made largely of carbon fibre with more systems running on electric circuits, which is far more fuel-efficient than most other aircraft.

But a spate of incidents involving the main, lithium-powered battery packs – including two fires on planes operated by Boeing's first Dreamliner customer, All Nippon Airways – saw US safety authorities recommend the grounding of the entire worldwide fleet for three months this year.

In the UK, British Airways took delivery of the first of 24 Dreamliners it has ordered two weeks ago, while Thomson Airways has already started flights.