Boeing Co's proposal for preventing battery problems that have grounded its entire fleet of 50 787 Dreamliners is not a temporary stop-gap measure aimed at getting the airplanes flying again, three sources familiar with the plan said.

he proposal, being made to the U.S. 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.

(Reporting by Andrea Shala-Esa and Alwyn Scott; Editing by Gerald E. McCormick)