Boeing said its flight of a 787 on Friday will wrap up the testing for its fix of the battery problems that have kept the plane grounded.

The flight took off at 10:39 a.m. Pacific time from Paine Field in Everett, Wash., according to FlightAware.

The flight is the certification test for a new battery system. The test was "to demonstrate that the new system performs as intended during normal and non-normal flight conditions," Boeing spokesman Marc Birtel said in a written statement.

The 787 Dreamliner has been grounded since January because of smoldering batteries, including a fire on the ground in Boston. Boeing has designed what it says is a fix, including more heat insulation and a battery box designed so that any meltdown of the lithium-ion battery will vent the hot gases outside of the plane.

On March 12, the Federal Aviation Administration approved Boeing's plan to test the redesigned battery system, and Friday's flight test was the final part of that plan. The flight was to demonstrate the battery fix for the FAA.

The same plane, built for LOT Polish Airlines, flew on Monday in a pre-delivery check flight, where pilots did things like raise and lower the landing gear and ran backup systems.

The FAA will still need to approve the results and certify the battery system before airlines can fly 787s again. Fifty 787s owned by eight airlines have been grounded worldwide. Boeing has said it will install the battery fix on those planes first, and then on the 787s it has continued to build while the planes have been grounded.

The root cause of the battery problems still isn't known. Boeing executives have said that other airplane problems have been fixed without understanding exactly what caused them.