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Hot chemicals sprayed out of the battery on the 787 Dreamliner in this week’s emergency landing in Japan, leaving a gooey dark residue and suggesting a different malfunction than last week’s 787 battery fire in Boston, according to two people with knowledge of the situation.

The residue covered the battery and splattered over nearby instruments inside the forward electronics bay. It left a 12-foot-long dark streak from the battery to an outflow valve through which some of the spray vented overboard during the flight.

The people with knowledge of what was found inside the forward electronics bay after the incident said the battery was not blackened and cracked open like the battery in the Japan Airlines 787 fire a week earlier at Logan airport in Boston.

“It’s not as bad as the earlier incident,” one person said, speaking on condition of anonymity. “It looks like there wasn’t a fire. But there was a significant overheating.”

Two further sources confirmed that there was no fire inside the airplane.

The residue may have been from smoke or from hot, vaporized electrolyte, the potentially flammable chemical inside the battery.

But even without a fire, “it’s still a problem” that the electrolytes sprayed out of the battery box, said one person.

Four independent control circuits govern how the battery charges, ensuring that it neither over-charges nor discharges too much.

Boeing believes these circuits may have done their job as designed and stopped the overheating before a fire could start, one person said.

Boeing senior vice president Mike Sinnett, who is responsible for the plane’s electrical systems, said in an interview last week following the Logan fire that those controls, two inside the battery and two external, would prevent any serious battery incident.

He added that Boeing tests showed that any smoke from a less serious battery overheating incident in flight would exit through the outflow valves overboard, ensuring none entered the passenger cabin or the cockpit.

But the Federal Aviation Administration (FAA), announcing its decision Wednesday to ground the 787 fleet, indicated it is not satisfied that these systems worked as designed. It stated that both battery incidents resulted in the “release of flammable electrolytes, heat damage, and smoke.”

ANA said Wednesday that the pilots did smell something that they thought was smoke, and that this smell was also in the passenger cabin.

That, along with warnings of battery trouble on the instrument panel, is what impelled the pilot to make the emergency landing, deploy the emergency exit slides and evacuate all 137 passengers and crew.

Two people with knowledge of what happened said the pilot received three battery warning messages during take-off after an initial status message.

One of those messages warned that the battery was overheating.

The 787 batteries are made by GS Yuasa of Japan. Its manufacturing processes will likely be the immediate focus of attention once investigators learn precisely what went wrong in each of the two incidents.

Dominic Gates: (206) 464-2963 or