Top Boeing brass appeared confident Friday in their “comprehensive” solution to the company’s 787 battery problem, and predicted a swift return to flight for the grounded jet.

The company’s commercial aircraft chief and its lead 787 engineer spoke from Japan, the home of the jet’s first two customers and the site of an in-flight battery malfunction that prompted the global grounding. They said the work of hundreds of Boeing engineers had led to a multi-part redesign that meant there would never be another fire, such as the one in January on a plane parked in Boston.

Then, some 14 hours later when morning had reached the American East Coast, another top 787 engineer said Boeing has already passed some of its tests and expects to hand over all of its results to the Federal Aviation Administration “within the next week or two.”

The regulatory agency had announced Tuesday its approval of Boeing’s plan to test its 787 battery.

While variables still loom on the horizon, aviation analyst Richard Aboulafia was among those who sensed that Boeing is aggressively turning the corner on its mysterious and expensive battery problem.

“It still seems like a very ambitious schedule, but on the other hand it looks like the FAA might be coming around,” said Aboulafia, vice president of analysis with Teal Group in Fairfax, Va.

Among the new details of the fix revealed Friday:

A phonelic glass laminate that will insulate the cells within each lithium-ion battery from each other and their container.

A stainless steel airtight containment box that will prevent, through oxygen evacuation, any overheating from igniting.

One-inch titanium tubes that will vent any pre-fire heat from the battery out of the airplane entirely.

“With these changes, we think the likelihood of a repeat event is very unlikely,” said Ron Hinderberger, vice president of 787-8 engineering. “That said, I have no intention whatsoever of sitting here in front of you today and telling you we will never have a battery failure.”

Mike Sinnett, the 787’s chief project engineer, said the fix would add 150 pounds to the airplane, making the lithium-ion battery’s weight savings a “wash.” But he and Hinderberger said the other advantages of the high-tech battery, such as increased power and easier maintenance, still made it the choice over older nickel-cadmium batteries.

Aboulafia said the extensive electric system on the 787 would make such a switch, which Boeing’s rival Airbus is making on its answer to the Dreamliner, the A350, difficult. As for the safety modifications Boeing chose instead, Aboulafia was pleasantly surprised if still not completely sold.

“It’s a little more comprehensive a fix than I expected, and that’s good,” he said, “But still, it’s not really clear what the Plan B is, if anything.”

Neither Boeing nor any of the government investigators have yet determined the root cause of the battery incidents, and Sinnett admitted they might never know. But Boeing’s engineers, along with outside battery experts, have brainstormed the possible failures and made sure the box and venting system can handle them.

The 787 Dreamliner was grounded on Jan. 16 after the pair of smoky battery incidents. Boeing had delivered 50 787s by that point, including four made in North Charleston.

Boeing South Carolina was not involved in either the fix or the testing, a spokesman confirmed, noting that Boeing’s systems engineers are based in Washington state.

“So it wasn’t a conscious decision to exclude South Carolina,” said Tim Neale, the Boeing spokesman. “It’s just it worked out that way because of where we had certain capabilities and where we did not.”

The National Transportation Safety Board has been investigating the Jan. 7 Boston fire, and Chairwoman Deborah Hersman has said a short circuit led to “thermal runaway” and fire in the battery.

Boeing disputes that term. Hinderberger instead called the accelerating overheating “thermal propagation.” He also noted that the fire was not in the battery box.

An NTSB spokesman Friday said he could address only his agency’s definition of the term.

“We have defined thermal runaway as an uncontrolled chemical reaction occurring at high temperatures, which is what we saw in Boston,” he wrote in an email.

Hinderberger declined to speculate how long the FAA might take to decide on the results submitted by Boeing.

If the fix is accepted, Boeing would recall, retrofit and retest the more than 100 batteries (two per plane) that have been delivered to customers. Hinderberger said some would fail, but neither he nor Neale could say how many.

Going forward, Boeing and its battery system suppliers would institute a much more rigorous testing regime.

While everyone hopes the fix works, Aboulafia noted that this isn’t the first time Boeing has hustled to come up with a solution to get its planes into revenue service for its customers. Other times they haven’t worked as planned, leading to a more than three-year delay in bringing the new jet to market

“The history of this program is a story of aggressive assumptions that aren’t always warranted,” he said.

Reach Brendan Kearney at 937-5906 and follow him on Twitter at @kearney_brendan.