US regulators are close to approving a key document that could start the process of returning Boeing Company's grounded 787 Dreamliner to service within weeks, according to several people familiar with the matter.

Approval of the document, known as a project statement of compliance, would mark a decisive step towards ending the three-month grounding of Boeing's high-tech jet. It would kick off a series of procedural steps allowing airlines that ordered the $200 million plane to fly them for the first time since January.

The grounding has cost Boeing an estimated $600 million, halted deliveries and forced some airlines to lease alternative aircraft. Several airlines have said they will seek compensation from Boeing, potentially adding to the planemaker's losses.

Regulators grounded the worldwide fleet of 50 jets after lithium-ion batteries burned on two planes at the start of the year. Boeing redesigned the battery system and sent test results to the Federal Aviation Administration earlier this month.

The document could be approved as early as next week, said two of the sources, asking not to be identified because the discussions remain confidential.

The FAA declined to comment on whether Boeing had already submitted the document, the exact contents of which are unclear.

Boeing also declined to comment beyond saying that it stands ready to continue working with the FAA "to ensure we have met all of their expectations."

The timing has not been fixed and could still be delayed, the sources said. It's also possible that extra steps could be added to the approval process, resulting in further delays and prolonging the uncertainty around if and when the 787 can fly again.

Approval early next week would coincide with a two-day investigative hearing into the burnt batteries by the top US safety regulator, the National Transportation Safety Board. The hearing is expected to call on officials from the FAA and Boeing.

NO TIMETABLE

The FAA has said it is considering Boeing's proposed battery fix, but has not indicated a specific timetable for approval. On Tuesday, FAA chief Michael Huerta said he expects to decide "very soon" whether to approve the new system.

However, Huerta also stressed to a congressional committee that the agency is reviewing tests and analysis submitted by Boeing and will approve it when "we are satisfied Boeing has shown the redesigned battery system meets FAA requirements."

After approval of the project statement, Boeing would draft a "Service Bulletin," formally telling airlines to retrofit the new batteries on the 50 planes already delivered worldwide. The FAA would have to approve the design change and the service bulletin, and then issue an "Airworthiness Directive" declaring the flight ban over.

Sources say Boeing has already assembled teams and battery kits to retrofit existing planes, and engineers would need around four to five days to fit each new battery, allowing for a progressive return to service, starting in Japan.

All Nippon Airways and Japan Airlines own nearly half of the current 787 fleet and would be retrofitted first. United Airlines is the only US carrier that has the jet currently. It was not immediately clear where United would fall in the order of repairs.

United and other airlines have been moving up the date when they will add the 787 to their flight schedules to May and June, a sign of growing confidence that FAA approval will come soon. – Reuters