he proposal, being made to the US Federal Aviation Administration on Friday, includes specific measures aimed at addressing possible causes of short-circuits that prompted one of the lithium-ion batteries on board a 787 to catch fire at a Boston airport in January, the sources said. A second battery smoldered during a flight in Japan a few days later, leading to an emergency landing and evacuation.

The proposal includes insulation between the cells of the battery and a stronger, stainless steel box with a venting tube to contain a fire and expel flames outside the aircraft should a battery catch fire again, the sources said.

Boeing will not propose abandoning lithium-ion batteries, however, and is not working on a backup or longer-term fix, the sources said.