Updated Wednesday, January 9, 2013 at 08:43 PM
The fire aboard an empty 787 Dreamliner parked at Boston's airport Monday left the floor of the jet's electronics bay blackened and plastic dripping underneath — and that was after firefighters ripped out and tossed a burning high-energy, lithium-ion battery onto the tarmac, according to a person with inside knowledge of the investigation.
The incident caused "severe fire damage" to the electronics bay, the National Transportation Safety Board (NTSB) said.
It also heightened scrutiny of the plane's innovative electrical systems, particularly after earlier problems with the 787's power-distribution panels, including an incident last summer that has not been previously disclosed.
The battery fire occurred after the 183 passengers and crew on the Japan Airlines flight had disembarked from a 12-hour trans-Pacific flight from Tokyo. But the person with inside knowledge said it can't be ruled out that such a problem could recur in flight — a nightmare scenario for any airline.
"That battery is charged off the normal electrical system in flight," he said. "It pretty well stays charged all the time."
Yet 787 Chief Project Engineer Mike Sinnett in an interview Tuesday steadfastly defended the Dreamliner's safety systems.
Sinnett wouldn't discuss the specifics of the fire at Logan International Airport because of the investigation, but he spoke in detail about the safety of the 787's lithium-ion batteries.
"I'm still very confident that any (battery) failure I would ever expect to see on an airplane in flight can be contained by the system," said Sinnett. "We feel confident it's a robust design."
Sinnett also gave details about the four previous incidents involving electrical failures on 787 passenger flights operated by United, Qatar Airways and another airline.
Although these were unrelated to and less serious than the Logan fire, they were more than the false warnings previous reports had suggested.
Sinnett confirmed that those earlier incidents were traced to faulty circuit boards inside power-distribution panels in the same electronics bay. He said electrical arcing inside the boards damaged their functionality and shut down some of the plane's electrical power.
But he said the sparking inside the circuit boards was tiny — "a low energy arc that lasted milliseconds, very small" — and produced no safety hazard, only a loss of function that was handled by the plane's multiple, redundant power systems.
The Dreamliner — whose electrical systems generate 1.45 megawatts of electricity, enough to power 600 homes and four times as much as a larger 777 jet — carries two large lithium-ion batteries, located in forward and rear electronics bays.
The battery in the rear bay that caught fire is about one and a half times the size of a car battery.
It's used to start the auxiliary power unit (APU), a small turbine engine in the tail that is used to provide electrical power while the plane is on the ground, or as a backup power source during an in-flight emergency.
According to NTSB preliminary findings, airplane maintenance and cleaning personnel were on the airplane with the APU in operation when they observed smoke in the cabin.
Emergency personnel who responded "detected a fire in the electronics and equipment bay near the APU battery box," the NTSB stated. "The fire was extinguished about 40 minutes after arrival of the first rescue and fire personnel."
"One firefighter received minor injuries," the NTSB said.
Aviation analyst Scott Hamilton of Leeham.net said he expects the Federal Aviation Administration (FAA) to soon issue an airworthiness directive mandating some precautionary actions.
"I'd be surprised if the FAA doesn't quickly come out with an inspection order," Hamilton said. "Airlines are going to be doing this anyway."
Monday's fire at Logan follows an in-flight fire during a 2010 Dreamliner test flight, and the four more recent incidents involving faulty electrical panels while the jet was in service.
Sinnett said the first of the electrical-panel problems occurred last summer. He didn't name the airline, but back then only All Nippon Airways and Japan Airlines were flying the Dreamliner. The incident wasn't made public at the time.
He said the issue occurred again in December on a United flight that had to be diverted to New Orleans; a few days later on a Qatar delivery flight from Everett to Doha; and then again on a second United jet.
United in late December reported "sporadic issues with our 787 generators and power distribution panels."
Sinnett said all four incidents were traced to faulty circuit boards from a single manufacturing batch.
The person with knowledge of the problems said the flawed circuit boards are manufactured in Mexico for United Technologies, which supplies the power distribution panels to Boeing.
However, the person said the only impact of the arcing in the circuit boards was to cut off some of the plane's power supply from a generator, but not enough to present any safety issue. None of the planes involved was ever in danger, the person said.
Sinnett said Boeing is still working to fix that problem.
Despite those in-flight incidents, he said, the 787 is "running at a high dispatch reliability, on a par with where we were on the 777 at this point."
Latest more serious
The Logan fire incident is much more serious, however.
In 2007, the FAA noted that the large, high-capacity, rechargeable lithium-ion batteries Boeing is using on the Dreamliner differ significantly from the nickel-cadmium or lead acid batteries used on other jets.
Commercial aviation has "limited experience" with such batteries, the agency said, noting that in other applications "lithium ion batteries are significantly more susceptible to internal failures that can result in self-sustaining increases in temperature."
Also, overcharging of lithium-ion batteries can generate high temperatures so that "the metallic lithium can ignite, resulting in a self-sustaining fire or explosion," the FAA said.
Because of those concerns, the agency attached special safety conditions governing the design and maintenance of the 787 batteries.
It said the jet's batteries must specifically preclude any heat buildup and include monitoring and warning systems in case of any failures.
Sinnett said Boeing has met those design requirements.
He said there are four levels of protection to prevent the most dangerous scenario, that the battery overcharges.
Addressing an online report by The Wall Street Journal Tuesday that when United inspected its Dreamliner batteries after the Logan fire, it found some faulty wiring installed, Sinnett insisted the battery system is designed so that problems with the wiring cannot cause a fire.
He said that although the 787 uses more electric power, it uses correspondingly less hydraulics and less pneumatics.
That means less high-pressure fluid and less hot, high-pressure air moving around the aircraft in titanium ducts.
The total horsepower generated by the 787's engines in cruise flight is actually less than on a conventionally powered aircraft, Sinnett said, and as a result there's "less potential for something bad to happen."
50 in service
Boeing has delivered 50 Dreamliners to airlines. Boeing's marketing vice president, Randy Tinseth, wrote Tuesday on his blog that the plane has flown more than 18,000 flights and logged more than 50,000 hours.
The NTSB now has three safety investigators examining the cause of the Logan fire as well as the fire and airport emergency response to the incident.
The FAA and Boeing are also taking part in the investigation.
The Japan Transport Safety Board has sent a representative and Japan Airlines will assist.
The latest incidents, including a fuel spill from another JAL 787 at Logan on Tuesday, rattled investors.
Boeing shares fell $2, or 2.6 percent, to close at $74.13.
Dominic Gates: 206-464-2963 or email@example.com
NTSB investigator Mike Bauer works inside the 787 under fire investigation at Boston's Logan Airport. The space in front of his hand is where the lithium-ion battery was.