By Sylvia HuiLONDON -- A fire on an empty Boeing ( BA) 787 airliner at London's Heathrow Airport does not appear to have been caused by faulty aircraft batteries, a British investigative agency said Saturday. Investors in Boeing, which calls its newest plane a Dreamliner, had feared that Friday's blaze meant that a battery overheating problem that grounded the whole fleet of such planes in January had not been fixed. News of the fire on the Ethiopian Airlines plane sent Boeing shares down 4.7 percent on Friday. But Britain's Air Accidents Investigation Branch said there was "no evidence of a direct causal relationship" between the Dreamliner's batteries and the fire. "There has been extensive heat damage in the upper portion of the rear fuselage, a complex part of the aircraft ... it is clear that this heat damage is remote from the area in which the aircraft main and APU (auxiliary power unit) batteries are located," the agency said in a statement. Ethiopian Airlines said it was continuing to operate its fleet of 787s despite the investigation, which will take at least several more days to be completed. The airline's chief executive, Tewolde Gebremariam, told The Associated Press on Saturday that there is "no flight safety issue" with the 787s and that Ethiopian Airlines, like other operators, hasn't made changes regarding the planes. Friday's fire broke out more than eight hours after the plane landed at Heathrow Airport. The aircraft was parked on a remote parking stand with no one onboard when smoke was detected from it, Ethiopian Airlines said. Although the incident caused no injuries, it forced Heathrow, one of the world's busiest airports, to close its runways for nearly an hour. Arrivals and departures were briefly suspended, delaying hundreds of passengers' journeys. The fire also drew renewed attention to the future of Boeing's most technologically advanced airliner. Boeing, based in Chicago, marketed the 787 as a revolutionary jet which burns 20 percent less fuel than comparable aircraft, thanks to its lightweight design. In another first, the plane relies on rechargeable lithium-ion batteries to start its auxiliary power unit, which provides power on the ground or if the main engines quit. But problems with those batteries led to the grounding earlier this year of the 50 Dreamliners flying at the time.