The FAA has approved Boeing’s design modifications to the 787 battery system, a move that will allow the aircraft to reenter service once the changes are made to the fleet and verified by the FAA.

The approval, which will be official next week upon publication of a final directive and “instructions to operators for making the changes,” ends a three-month grounding of the widebody resulting from two incidents of smoke and fire from the 787’s lithium-ion battery systems.

Two weeks ago Boeing completed its final certification test for the redesign, which included containment and venting systems for the main and auxiliary system batteries, modified charging systems and new batteries. The FAA on April 18 granted Boeing permission to resume routine production ‘B-1’ flight testing of an aircraft destined for All Nippon Airways (ANA).

“The changes are designed to address risks at the battery cell level, the battery level and the aircraft level,” says the FAA.

FAA ruling comes just days before the NTSB is to hold a one and half-day “investigative review” on the battery failures starting April 23.

The FAA says it will “closely monitor” the modifications of the aircraft in the U.S. fleet “to assure proper installation of the new design” and that each modification will need its approval before the aircraft can be returned to service.

Boeing says each modification is expected to take up to five days to perform, with the first 787s expected to return to service in May or June.

The FAA says it will support other aviation authorities worldwide to finalize return to service procedures there.