WASHINGTON (AP) — Federal officials said Thursday they are investigating an unusual rolling motion on a Southwest Airlines Boeing 737 Max that might have been caused by a damaged backup power-control unit. The Federal Aviation Administration said it was working with Boeing and the National Transportation Safety Board to investigate the May 25 incident, which happened on a flight from Phoenix to Oakland, California. The FAA said the plane went into a “Dutch roll,” the name given to the combination of a yawing motion when the tail slides and the plane rocks from wingtip to wingtip.