A Boeing 787 flew from Fort Worth to Washington Thursday, the first flight of the Dreamliner jet since January 16th, when two battery fires lead to a grounding of the aircraft.
Boeing got permission from the Federal Aviation Administration to return the plane to Washington State to get it ready for delivery to a Chinese airline.
Meanwhile, in Washington, DC National Transportation Safety Board Chairman Debbie Hersman said investigators think they know what caused the battery fires.
"This investigation has demonstrated that a short circuit in a single cell can propagate to adjacent cells and result in smoke and fire," Hersman explained.
But they can't explain yet why there's a short-circuit.
Hersman says it'll be weeks before an interim report is ready, meaning the grounding of the Dreamliner will continue.
"The decision to return the 787 to flight will be made by the FAA, not the NTSB," Hersman added.
She did ask the FAA to reconsider its certification process for the battery, which she says is unique to the 787.
The NTSB is focusing on the battery fire on a Dreamliner that landed in Boston in January.
Boeing technicians were paying particular attention to the battery on the Texas to Washington flight, which arrived without incident.
-- Chris Clackum reports