Experts at the Federal Aviation Administration are expected to say next week whether they recommend accepting Boeing Co.’s plan to fix its troubled 787 Dreamliners so the planes can resume flying, the agency head said Wednesday.

Experts in the FAA office that certifies new planes as safe for flight are reviewing a Boeing proposal to revamp the 787’s lithium ion batteries to prevent them from catching fire, or to protect the plane in case of fire, Administrator Michael Huerta said.

Once he receives the experts’ evaluation, it’s still up to Huerta to decide whether to accept the plan. He declined to say when he might make that decision, or how long it might be before the planes are back in the air.

“It’s a very long proposal, a lot of technical detail in it,” Huerta said. “I’m reviewing it myself, as well as relying on the teams that are reviewing it.”

The planes have been grounded since Jan. 16 after one battery caught fire and another began smoking during a flight.

Calling the plan “very comprehensive,” Huerta said Boeing engineers worked with outside experts to narrow the potential causes of the incidents to a few possibilities, then redesigned the batteries.

The 787 has two identical 32-volt batteries, each with eight cells.

Investigators have said the incidents began with short-circuiting in a single cell, leading to a chemical reaction that causes progressively hotter temperatures. That spread the short-circuiting and fire to other cells.

Boeing’s plan includes redesigning the batteries to prevent individual cells from catching fire, Huerta said.

Should that fail, the plan includes steps to prevent a fire from spreading to other cells or outside the box that contains all eight cells.