US air-safety regulators on Tuesday approved Boeing's plan to fix 787 batteries for testing, a major step forward to get the planes, grounded worldwide, flying again.
"The Federal Aviation Administration today approved the Boeing Commercial Airplane Company's certification plan for the redesigned 787 battery system... and the company's plan to demonstrate that the system will meet FAA requirements," the agency said in a statement.
The FAA said it had given the green light after "thoroughly reviewing" Boeing's February 22 plan to address risks after lithium-ion batteries short-circuited on two 787 Dreamliner aircraft in mid-January.
A short circuit started a fire on a parked 787 at Boston's Logan Airport and smoke from a battery forced an emergency landing in Japan.
The incidents led to the grounding of all 50 787s in service worldwide on January 16.
"The certification plan is the first step in the process to evaluate the 787's return to flight," the FAA said.
It "requires Boeing to conduct extensive testing and analysis to demonstrate compliance with the applicable safety regulations and special conditions."
The FAA said Boeing's battery improvements include a redesign of internal battery components "to minimize initiation of a short circuit within the battery."
Boeing said its fix also included the addition of new insulation materials, stepped-up production and testing processes, and a containment system.
"We've introduced a new enclosure system that will keep any level of battery overheating from affecting the airplane or being noticed by passengers," Ray Conner, head of Boeing Commercial Airplanes, said in the statement.
Boeing will run a series of tests and be allowed "limited" test flights for two aircraft equipped with prototype versions of the battery fix, it said.
"This comprehensive series of tests will show us whether the proposed battery improvements will work as designed," Transportation Secretary Ray LaHood said in the statement.
"We won't allow the plane to return to service unless we're satisfied that the new design ensures the safety of the aircraft and its passengers."
The FAA said it was continuing its comprehensive review of the design, production and manufacturing process of the cutting-edge jetliner, built largely with lightweight composite materials.
Boeing expressed confidence that its plan to address the problem will pass the test.
"Today's approval from the FAA is a critical and welcome milestone toward getting the fleet flying again and continuing to deliver on the promise of the 787," Jim McNerney, Boeing chairman, president and chief executive, said in a separate statement.
The Chicago-based company said it would provide additional details of the improvements in the coming days.