After a "thorough" review, the U.S. Federal Aviation Administration on Tuesday approved Boeing's certification plan for a redesigned battery system for the 787 Dreamliner. The certification plan marks the start of a process to evaluate the 787’s return to flight and requires Boeing to conduct what the FAA called extensive testing and analysis to demonstrate compliance with applicable safety regulations and special conditions.

“This comprehensive series of tests will show us whether the proposed battery improvements will work as designed,” said U.S. Transportation Secretary Ray LaHood. “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 improvements include a redesign of the internal components to limit the possibility of a short circuit within the battery, better insulation of the cells and the addition of a new containment and venting system.

“We are confident the plan we approved today includes all the right elements to conduct a comprehensive evaluation of the battery system redesign,” said FAA Administrator Michael Huerta. “Today’s announcement starts a testing process which will demonstrate whether the proposed fix will work as designed.”

The certification plan establishes specific pass/fail criteria for the series of tests needed to return the airplane to service. It also defines the parameters the tests should measure, prescribes the test methodology and specifies their format and design, said the FAA. Agency engineers will witness the testing and participate in all aspects of the process, it added.

The FAA has approved “limited” test flights for two aircraft outfitted with prototype versions of the new containment system. If successful, the flight tests would validate the aircraft instrumentation for the battery and testing of the battery enclosure as well as product improvements for other systems.

Neither the FAA nor the U.S. National Transportation Safety Board have determined the source of the January 7 fire aboard a Japan Air Lines 787 parked at Boston Logan Airport. Another case of battery overheating aboard an All Nippon Airways 787 flying over Japan on January 16 remains under investigation by Japanese authorities as well. All 50 of the 787s delivered to customers have sat grounded since then. Meanwhile, the FAA’s “comprehensive” review of the 787’s design, production and manufacturing process continues.