U.S. flight safety officials say they are reviewing a Boeing (BA) proposal about how to fix the 787 battery problems and return the fleet to flight status.

However, the U.S. Federal Aviation Administration says it will not reinstate the aircraft until it is fully confident the battery issue has been resolved.

“The FAA is reviewing a Boeing proposal and will analyze it closely,” the FAA said on Friday. “We won’t allow the 787 to return to commercial service until we’re confident that any proposed solution has addressed the battery failure risks.”

Boeing met with Federal Aviation Administrator Michael Huerta and other safety leaders on Friday afternoon in Washington D.C. to discuss a solution to the battery meltdown issues that triggered an emergency landing in Tokyo last month and forced the FAA to ground all 50 in-service jets.

Boeing said the meeting, which was run by Boeing Commercial Airplanes CEO Ray Connor, was “productive.” The two discussed the status of ongoing work to address the Dreamliner problems.

Boeing over the last few weeks has employed a fleet of hundreds of experts, which it says have been working around the clock to try and resolve the issues.

“We are encouraged by the progress being made toward resolving the issue and returning the 787 to flight for our customers and their passengers around the world,” a Boeing spokesman said.

The FAA grounded the planes in January amid problems with the 787’s lithium-ion battery. Earlier this month it allowed Boeing to begin test flights of the Dreamliner, however the cause of the fires and meltdowns remains unclear.

Earlier this week, reports indicated the 787 could return to service as early as April, however Boeing has not confirmed that timeline. Airlines have been adjusting their flight schedules over the next few months in anticipation of the Dreamliner’s unavailability, with United Airlines (UAL) on Thursday saying it was removing the 787 from its flight plans through June 5.

Boeing said it has been working closely with the FAA and other safety authorities and is committed to take “every necessary step” to assure the integrity of the 787.

Possible battery mends include placing a vent within the battery pack and spacing out the cells of the battery so as to ensure it doesn’t overheat or short circuit, according to Reuters. Boeing has not commented on the details of its plan to improve the battery’s safety.

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