More than three months after being grounded due to a fire on a Japan Airlines plane in Boston, Boeing's 787 Dreamliners have been given approval to take to the skies again—including on transoceanic flights—once they have been outfitted with modifications that passed testing under the FAA's scrutiny. The planes could be in the air again as early as next week.

In a prepared statement, FAA Administrator Michael Huerta said, “A team of FAA certification specialists observed rigorous tests we required Boeing to perform and devoted weeks to reviewing detailed analysis of the design changes to reach this decision.”

The Boston fire was the result of thermal runaway, a condition that occurs when a lithium-ion battery's temperature rises above 300 degrees Fahrenheit. Once the cell reaches that temperature, chemical reactions within the cell cause it to continue to overheat, potentially exploding and venting gases that could combine with combustible materials and catch fire. The rising heat in the cell could also cause a cascading effect with other cells. Multiple short circuits in one cell of the JAL 787's battery led to the thermal runaway, which did cascade to other cells and caused the battery to rupture and catch fire.

The new, improved battery system's design has been altered to prevent the sort of fault that led to the Boston fire and the failure of a battery on an All Nippon Airways 787 in January. There is added insulation between each cell to prevent a short-circuit within the lithium-ion cells from cascading to others.

Even if the battery does fail and overheat, Boeing officials said, its new sealed steel enclosure system, with cooling and venting, will prevent a fire and contain the problem to the battery itself, protecting the rest of the aircraft. As part of testing, propane was used to create a small explosion inside the enclosure, which was successfully kept contained within it. Boeing claims that the enclosure will not only isolate a possible battery failure from the rest of the aircraft's components, but that passengers won't even notice if a failure occurs.

There are some unanswered questions that remain. Boeing was never able to replicate the failure that caused the Japan Air Lines 787 to catch fire in its tests of the old design. And considering that the original reason Boeing selected lithium-ion batteries for the 787 was their relatively low weight, the additional provisions would seem to cancel out much of the benefit of the technology.

The decision by the FAA also means that Boeing can resume delivery of new 787s to customers. According to Boeing, the company expects to be able to deliver all of the planes scheduled for 2013 to customers by year's end.

Listing image by Kentaro Iemoto