Image caption No passengers were aboard the plane when it caught fire

Air accident investigators looking into the Boeing 787 Dreamliner fire at Heathrow last week may have identified the cause.

They have asked that all Boeing 787s switch off an electrical component until further notice.

In a statement, the Air Accidents Investigation Branch said a transmitter used to locate aircraft after a crash needed more "airworthiness actions".

Boeing said it "supports the two recommendations from the AAIB".

Last Friday, a fire on the parked Ethiopian Airlines plane closed Heathrow airport for 90 minutes.

The AAIB said the problem might not be confined to the 787 and recommended that regulators conduct a safety review of similar components in other aircraft.

The US airline regulator, the Federal Aviation Administration, said in a statement: "We are currently reviewing the AAIB's report and recommendations to determine the appropriate action."

Boeing reiterated its commitment to the expensive aircraft, saying: "We are confident the 787 is safe and we stand behind its overall integrity."

Later, a Tokyo-bound Dreamliner operated by Japan Airlines turned back after taking off from Boston's Logan International Airport, in what the airline called a "standard precautionary measure" after indicators warned of a mechanical problem.

It is not clear if the incident was related to the transmitter problem.

Different problem

At the start of the year, all 50 Dreamliners in service worldwide were grounded after two separate incidents concerning batteries.

What is an Emergency Locator Transmitter? Used to guide rescue crews to the location of an aeroplane if there is an accident

Resistant to damage in the event of a crash - like a black box

Activated either automatically, by means of a control panel, or manually, by a flight crew member

Can transmit for around 24-48 hours once activated

Not required to be on aeroplanes, but make it easier to locate one in the event of an accident

But the AAIB investigators found the fire damage to Ethiopian's aircraft was not near the batteries.

Instead, they have found that the fire was in the upper rear part of the 787 Dreamliner, where the Emergency Locator Transmitter (ELT) is fitted.

The AAIB statement said: "Detailed examination of the ELT has shown some indications of disruption to the battery cells. 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."

As the ceiling space where the ELT is located does "not typically carry the means of fire detection... 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".

Honeywell International, the company that makes the emergency transmitters, said it backed the proposal to switch them off while investigations continued, but said it was "premature to jump to conclusions".

ELT fires are extremely rare says Todd Curtis, a former Boeing aviation safety engineer and founder of AirSafe.com.

"In my professional experience, this is the first time I've ever heard of an ELT being associated with an aircraft fire," Mr Curtis told the BBC.

"So it's very definitely a high interest item."

Shares higher

Boeing's shares were up by more than 2% on news of the AAIB's findings.

"I think it does alleviate a lot of the fears that its another Boeing battery problem... [but] I don't think Boeing is out of the woods yet," Bloomberg Industries senior airline and aerospace analyst George Ferguson told the BBC.

The Dreamliner programme has been incredibly expensive for Boeing, costing somewhere between $6bn and $10bn.

But some analysts still remain upbeat about the aircraft's future.

"I still think the 787 is going to prove to be one of the most desirable aircraft ever built," said Ray Neidl, senior airline and aerospace analyst at the Maxim Group.

"There are cost efficiencies built into it... and from the customer standpoint it's a very comfortable airplane to travel long distances on."