Southwest Airlines Boeing 737 Max goes into "Dutch roll" during Phoenix-to-Oakland flight

Federal officials said Thursday they're investigating an unusual rolling motion on a Southwest Airlines Boeing 737 Max 8 that might have been caused by a damaged backup power-control unit.

The Federal Aviation Administration said it's working with Boeing and the National Transportation Safety Board to investigate the incident on a May 25 flight from Phoenix to Oakland. Southwest says it's working with the FAA and Boeing.

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. It's said to mimic the movement of a Dutch ice skater. It happened when the jetliner was at about 32,000 feet.