It's unclear what caused the small fire Monday aboard a Japan Airlines 787 parked at Boston's airport, renewing concerns about electrical systems on the relatively new Boeing jet.

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A small fire broke out Monday on a Japan Airlines 787 parked at Boston’s Logan International Airport, renewing concerns about electrical systems on the relatively new Boeing jet that uses considerably more electricity than any previous plane.

It’s unclear what caused the fire, which was discovered shortly after passengers disembarked at the end of a 12-hour flight from Tokyo.

But the incident follows a major in-flight fire during a November 2010 test flight and minor issues last month on two flights operated by United and Qatar Airways, each tied to the plane’s electrical systems.

Boeing spokeswoman Lori Gunter said there is no indication that the Logan fire is linked to the previous incidents.

The plane, Japan Airlines’ seventh 787, was delivered Dec. 20.

The Logan fire broke out at about 10:30 a.m. local time, less than a half-hour after Japan Airlines (JAL) Flight JL008 landed in Boston.

All 183 passengers and crew had left the airplane when a mechanic, who had come aboard for routine maintenance checks, saw smoke in the cabin, said Logan spokesman Richard Walsh.

About 40 firefighters and 15 firefighting vehicles quickly extinguished the blaze.

JAL said in a statement that the “smoke was discovered in the rear end of the cabin.”

“The smoke was traced to a fire from the battery used for the auxiliary power unit (APU) which was situated in an electrical room at the back of the aircraft,” JAL said.

JAL canceled Monday’s return flight from Boston to Tokyo and was working to reschedule.

Reports from the scene of the fire were confusing.

Walsh said firefighters, who used infrared equipment to find the fire, described its location as in the “midsection” of the airplane, not the rear.

“When we arrived, it was a heavy smoke, and that was in three minutes, so this was advancing,” Massachusetts Port Authority’s fire chief, Bob Donahue, told The Associated Press.

And Walsh said that while the firefighters were controlling the fire, one of the batteries used to power the APU “exploded,” causing a further flare-up.

“Something caused this battery pack to overheat, ignite,” Donahue said.

The National Transportation Safety Board announced it was sending an investigator to Boston to look into what it called the “Boeing 787 smoke event.”

Because many of the Dreamliner’s systems — from wing de-icing to brakes to engine start — are electrically powered, the jet uses much more electricity than other airliners: about 1.5 megawatts, or enough to power more than 600 homes.

The APU is supplied to Boeing by United Technologies, which also provides the new plane’s extensive power generation and distribution systems.

Used as a source of electrical power while the aircraft is on the ground or as a backup power source during an in-flight emergency, the APU is in the tail of the airplane.

That suggests JAL’s account is accurate: that the battery was in the rear electrical bay in the lower part of the aft fuselage.

That’s also the site of the aircraft’s power electronics cooling system, designed to dissipate all the heat generated by the heavy electrical loads.

The 787’s new electrical system first caught public attention in 2010 when a major fire broke out in flight.

That fire was attributed to a piece of metal that had worked its way into one of five electrical distribution panels and caused the system to short.

Boeing fixed it with a redesign of the panel to keep out foreign debris as well as software changes to enhance protection against electrical faults.

The recent incidents on board airline flights were less serious.

In early December, a United Airlines flight from Houston to Newark, N.J., was diverted to New Orleans after the pilot received cockpit warnings of an electrical generator failure.

“A power-distribution panel caused a nuisance generator-fault indication,” United said later. The panel was replaced and that jet was returned to service.

Later that month, a Qatar Airways 787 on a delivery flight from Everett to Qatar experienced something similar and was temporarily grounded.

Though the root cause of those two incidents has not been established, Gunter said both were traced to an electrical distribution panel in the rear electrical bay.

The 2010 in-flight fire started in the same bay.

“It is premature to discuss today’s event in detail at this stage as the investigation is ongoing,” said Gunter, the Boeing spokeswoman. “However, nothing that we’ve seen with the Boston event indicates a relationship to the December events or to the 2010 fire.”

Dominic Gates: 206-464-2963 or