The first report of a possible fire came from a cleaning worker just minutes after the passengers and crew had left a Boeing 787 jet that had landed shortly before at Logan International Airport in Boston. A cleaning worker noticed ‘‘an electrical burning smell and smoke’’ in the back of the cabin, according to a report released Thursday by the National Transportation Safety Board.
A mechanic then saw and smelled smoke there before seeing two distinct flames about 3 inches long at the front of the case holding the plane’s lithium-ion battery in the electronics bay.
Other managers reported smoke in the nearly empty passenger cabin that was intense and caustic smelling before summoning firefighters, who found a white glow with radiant heat waves coming from the battery, the report said.
The battery was also hissing loudly and leaking liquids and seemed to be reigniting. Standard fire suppressants had little effect, the report said, and a fire captain’s neck was burned, he said, when the battery exploded.
The new details about the fire were part of a preliminary report that indicates that the board has still not made much progress in figuring out why a battery in the new Boeing 787 jet parked at the airport burst into flame on Jan. 7.
The report echoed statements by Deborah A.P. Hersman, the board’s chairwoman, who told reporters last month that the problems seemed to have originated in the battery, when one of the eight cells had a short circuit.
While the safety board plans to continue its investigation, it said it would also hold a hearing on the hazards of the new lithium-ion batteries next month.
The 48-page report and nearly 500 pages of supporting materials added a few technical details about the condition of the charred battery, even if they did not advance efforts to pinpoint the cause of the fire.
The report said the airplane involved in this incident was delivered to Japan Airlines on Dec. 20. At the time of the fire, it had logged only 169 flight hours and 22 flight cycles.
The airline had flown the jet from Narita, Japan, and it touched down in Boston at 10 a.m.
The flight data recorder showed that at 10:04 a.m. the pilots started the auxiliary power unit, which is energized by one of the plane’s two batteries, to provide power on the ground. All the passengers and crew members had left the plane by 10:20, and the first reports of smoke came shortly after that.
The recorder showed that the battery failed at 10:21 a.m., and the plane’s electronic system automatically shut down the power unit 12 seconds later.
The incident was the first sign of trouble with the volatile new batteries on the 787. The planes were grounded worldwide nine days later after another 787 made an emergency landing in Japan when the pilots smelled smoke.
Over the past two weeks, Boeing has told the US government that it had identified the most likely ways in which the batteries could fail, and it proposed several fixes. Boeing contends that the changes would minimize the odds of incidents and protect the plane and its passengers if a problem did arise. The safety board released its report a day after federal officials said that the Federal Aviation Administration was close to approving tests of Boeing’s approach to fixing the batteries on its 787 jets, and the tests could begin next week.
The FAA could still demand changes in Boeing’s proposed battery design if problems develop in the laboratory and flight tests, which will take several weeks. But the decision to start the tests will be a major step in Boeing’s efforts to get the jets back in the air. They have been grounded since mid-January.
The federal approvals are expected late this week or early next week, though some battery specialists remain concerned that investigators have not found the precise cause of two incidents in which the jetliner’s new lithium-ion batteries emitted smoke or fire.
The plan is still subject to approval by Michael P. Huerta, the head of the FAA, and Ray LaHood, the transportation secretary, who will be briefed within several days.
LaHood said in January that the planes ‘‘won’t fly until we’re 1,000 percent sure they are safe to fly.’’