Officials in the FAA office in Renton 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.
Huerta declined to say when he might decide whether to accept the plan or how long it might be before the planes are back in the air.
Boeing officials presented the plan to Huerta last week.
The planes have been grounded since Jan. 16 after a battery caught fire in a 787 parked at Boston's Logan International Airport and a smoking battery in a different 787 forced an emergency landing in Japan.
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, and 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 of the cells.
"What Boeing has assembled is a team to look at the universe of potential causes, and their proposal is to mitigate all of them," Huerta said.
If the plan is approved, the next step would be extensive engineering and testing before any final determination could be made on resuming flights, he said. He described the process as "effectively a certification plan."
"We have to be assured that this is a good plan and that it is going to result in a safe situation," Huerta said.