Boeing conducted another 787 test flight on Monday as it tries to find out what caused battery problems that have knocked the plane out of airline service.

The flight took off from Boeing Field in Seattle, according to flight-tracking service FlightAware.

Federal officials grounded the 787 on Jan. 16 after two battery incidents in less than two weeks, including a fire. The order barred Boeing test flights, too. Boeing won permission for test flights last week, and the first one was conducted on Saturday. Boeing said the flight had 13 flight test workers and pilots, and was uneventful.

The flights are being done on one of Boeing's fleet of six 787 test planes that were used for flight testing before the plane went into full production. The plane has special equipment that allows the crew to observe and record detailed information about the performance of the two lithium-ion batteries on the plane.

Boeing did not release any details about what it found on the Saturday flight. It has also not said how many test flights it plans.

In an annual filing on Monday, Boeing Co. said it is too soon to estimate how much the 787 problems will cost. The financial impact will depend on what the cause turns out to be, how long it takes to find it, and the fix required to get 787s flying commercially again, the company said.

Shares of the Chicago-based company fell 69 cents to close at $76 in trading in New York.