WASHINGTON – Boeing attempted a major step Friday toward getting its 787 Dreamliners flying again, proposing a fix for the plane’s troubled batteries that could allow the flights to resume as early as April, congressional officials said.

The next question is whether the Federal Aviation Administration will agree to let the planes fly even though the root cause of a battery fire in one plane and a smoking battery in another is still unknown.

A Boeing team led by CEO Ray Conner presented the plan to Federal Aviation Administration head Michael Huerta. The airliners, Boeing’s newest and most technologically advanced, have not been allowed to fly since mid-January.

The plan – a long-term solution, rather than a temporary fix – calls for revamping the aircraft’s two lithium ion batteries to ensure that any short-circuiting that could lead to a fire won’t spread from one battery cell to the others, officials said. That would be achieved by placing more robust ceramic insulation around each of the battery’s eight cells. The aim is to contain not only the short-circuiting but also any thermal runaway, a chemical reaction that leads to progressively higher temperatures.

The additional spacers will enlarge the battery, requiring a bigger battery box to hold the eight cells. That new box would also be more robust, with greater insulation along its sides to prevent any fire from escaping and damaging the rest of the plane, officials said.

The plan will require testing and partially recertifying the safety of the plane’s batteries, said the officials, who spoke on condition of anonymity because they weren’t authorized to speak publicly.

The testing and recertification will take time, with engineers currently estimating completion sometime in April at the soonest, they said. Even after the batteries are recertified, it could take some more time to get the planes back into the air. Boeing will have to send teams to seven airlines in six countries to retrofit their planes.

It’s up to Huerta to decide whether to approve the plan. But Boeing’s plan is not a surprise, since the company has kept regulators closely informed, the officials said.

The 787 is the world’s first airliner made mostly from lightweight composite materials. It also relies on electronic systems rather than hydraulic or mechanical systems to a greater degree than any other airliner. And it is the first airliner to make extensive use of lithium-ion batteries, which are lighter, recharge faster and can hold more energy than other types of batteries.