* Dreamliners grounded earlier this year due battery problems
* Boeing says has people working to understand cause
* Images show damage to plane away from battery locations
* Former investigator cautions against early conclusions
* Boeing shares close 4.7 percent lower
By Rhys Jones
LONDON, July 12 (Reuters) - A Boeing 787 Dreamliner operated by Ethiopian Airlines caught fire at Britain’s Heathrow airport on Friday in a fresh blow for the U.S. planemaker which earlier this year was forced to ground the new planes for three months because of overheating batteries.
Boeing shares closed down 4.7 percent at $101.87. Earlier in the session they tumbled as much as 7 percent, wiping $5.4 billion off its market capitalisation after television footage showed the Dreamliner surrounded by foam used by firefighters at Heathrow.
Heathrow briefly closed both its runways to deal with the fire which broke out while the aircraft was parked at a remote stand. There were no passengers aboard the plane.
Television footage showed an area on the fuselage in front of the tail that appeared to be scorched.
“A Boeing 787 Dreamliner suffered an on board internal fire,” a Heathrow spokeswoman said. “The plane is now parked at a remote parking stand several hundred metres away from any passenger terminals.”
It was not clear if the fire was related to the batteries, which were the cause of the previous incidents that led to the grounding of the Dreamliner in January.
The Dreamliner’s two battery compartments are low down, according to public Boeing diagrams, while the visible damage to the Ethiopian plane appears to be higher up and further towards the rear, according to footage from the scene.
Former U.S. National Transportation Safety Board Chairman Mark Rosenker said the Heathrow incident was extraordinary news, coming so soon after the fleet had returned to service, but he cautioned against jumping to conclusions.
“It’s very early. No one knows where the fire started at this point,” Rosenker told Reuters, adding it could be something as simple as a coffee pot left on in a galley.
Boeing said it was aware of the fire and that had people on the ground working to understand the causes of it. The U.S. Federal Aviation Administration said it was aware of the fire and was in contact with Boeing.
“This is terrible for the Dreamliner, any event involving fire and that airplane is going to be a PR disaster for Boeing,” Christine Negroni, an aviation writer and safety specialist based in New York, said in a telephone interview.
“Because of the battery issue, the public is even more sensitive to events that happen to the Dreamliner. Even if they are normal, benign teething problems, that subtlety is going to be lost on the public,” she said.
Another Boeing Dreamliner operated by Thomson Airways returned to the United Kingdom due to technical issues as a precaution, TUI Travel said.
Ethiopian Airlines said its aircraft had been parked at Heathrow for more than eight hours before smoke was detected.
Richard Aboulafia, a senior aerospace analyst at the Teal Group in Virginia, said early evidence, including images of the jet, suggest the battery is not the issue because of the location of the fire.
Boeing’s 787 Dreamliner was grounded by regulators in January after batteries overheated on two of the jets within two weeks, including a fire at Boston airport on a parked Japan Airlines plane.
The Dreamliner resumed flying in April, with Ethiopian Airlines being the first carrier to put it back into passenger service.
The new high-tech jet came under intense scrutiny and Boeing redesigned the battery system to add more layers of protection against fire. Boeing began installing reinforced lithium-ion battery systems on the 787 in April.
Teams of engineers were dispatched by Boeing worldwide to install the stronger battery casing and other components designed to prevent a repeat of the meltdowns that led to the first U.S. fleet grounding in 34 years.
The plan approved by the Federal Aviation Administration called for Boeing to encase the lithium-ion batteries in a steel box, install new battery chargers, and add a duct to vent gases directly outside the aircraft in the event of overheating.
The 787 uses a powerful electrical system to drive air conditioning and hydraulic functions that are run from compressed air on traditional aircraft designs. That electrical system experienced fire during its development which also prompted changes in its electrical panels.
The Dreamliner which caught fire at Heathrow on Friday was delivered to Ethiopian Airlines in November last year.
It arrived at Heathrow from Addis Ababa in the early hours of Friday, according to the Flightradar monitoring web site. The plane was due to make the return journey later on Friday.
Asked whether the incident could lead to the renewed grounding of Dreamliner jets, a spokesman for Britain’s Civil Aviation Authority said decisions on the airworthiness of particular models of plane were made by the European Aviation Safety Agency (EASA).
An EASA spokesman said it was too early to say whether the aircraft would be grounded again.
United Continental and Polish airline LOT said they would continue to operate their 787s.
Ethiopian Airlines Dreamliners are powered by General Electric GEnx engines.