787 Fire Inquiry Focuses on Transmitter British safety investigators are examining whether a malfunction in an emergency locator transmitter or other equipment in the rear of a Boeing 787 Dreamliner caused the plane to catch fire on Friday at Heathrow Airport in London, federal and industry officials said Monday. The transmitter, which would send out the plane's location after a crash, is powered by a small lithium-manganese battery. The officials, who would speak only under the condition of anonymity because they were not authorized to discuss the inquiry publicly, said investigators were focused on whether the transmitter could have caused the fire or helped it spread. Honeywell Aerospace, which supplies the transmitter and the jet's navigation system, said Monday that it had sent technical experts to Heathrow to help the investigators. It said, however, that it was still "premature to speculate on the cause of the fire." The federal and industry officials said it was not clear if the transmitter, which was positioned near the top of the Ethiopian Airlines jet, malfunctioned or if the fire started close to it. The Air Accidents Investigation Branch in Britain has said it might release preliminary findings this week. Any suggestion that the transmitter was to blame would be a relief for Boeing. Honeywell and other companies supply similar devices for many passenger and business jets, and the best case for Boeing would be to have the problem traced to a generic piece of equipment instead of some of the novel systems on the plane. The plane's new electric and battery systems have led to problems in the early stages of the 787"s service even as airlines, attracted by fuel savings of 20 percent, continue to place orders for the aircraft. Still, it remained puzzling how the fire could have started because the empty jet had been parked for eight hours. Honeywell also noted in a statement on Monday that its transmitters had been certified by the Federal Aviation Administration since 2005, and "we've not seen or experienced a single reported issue on this product line." The transmitters have drawn such interest because they were situated directly beneath the searing heat damage that was visible in the crown of the plane's fuselage. They also stand out in their reliance on lithium since fire and smoke emitted from other lithium-ion batteries in January led to a four-month grounding of the 787s around the world. But the battery in the transmitter is much smaller and less flammable than the other lithium batteries, which can supply power when the plane is on the ground and provide backup power for the flight systems when it is in the air. Those batteries include cobalt, which is more volatile than manganese, a substance used in some electric cars and laptops. The larger cobalt batteries are also rechargeable, while the one in the emergency transmitter is not. Industry officials have said that the Ethiopian jet was connected to a ground power source. But the airline has said that the power was not on when the fire started. Hans J. Weber, the president of Tecop International, an aviation consultancy in San Diego, said that if the battery in the transmitter was not rechargeable, it was hard to see how it could have started the fire. "It's a passive device waiting to be activated in an accident," he said. While any battery can fail, he said, "it's an extremely unlikely event." He said the lithium manganese in the battery could have acted as "a hot spot" to accelerate a fire that started elsewhere, but "the fire would have had to have been pretty intense all by itself to set off the lithium in the device." The British investigators said Saturday that they had essentially concluded that the larger lithium-ion batteries played no role in the fire. But they have not yet released any other findings. The Ethiopian jet was parked in a remote part of the airport when the fire broke out on Friday. The fire occurred four and a half hours before the plane was scheduled to depart for Ethiopia. Peter Goelz, a former managing director at the National Transportation Safety Board in Washington, said that if investigators found that the emergency transmitter "was the major player in the fire," the Federal Aviation Administration will issue an airworthiness directive instructing airlines to inspect the devices on all passenger jets. Boeing and its suppliers have invested more than $20 billion in the Dreamliner, which uses lightweight carbon materials and more efficient engines to cut operating costs. The company has delivered 68 of the planes to 13 airlines, and it expects to sell thousands of the planes over the next two decades. Since the latest fire, the airlines with 787s have kept flying them and expressed confidence in the plane's safety. Shares of Boeing, which had risen more than 30 percent this year, dropped 4.7 percent on Friday after the news about the fire. The stock rebounded by $3.79, or 3.72 percent, on Monday, to $105.66.