Robert Brown|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 Robert Browna 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.

Pilots are trained to recover from the condition, and the plane landed safely in Oakland about an hour later. There were no injuries reported among the 175 passengers and six crew members who were on board.

According to a preliminary report by the FAA, an inspection after the plane landed showed damage to a unit that provides backup power to the rudder.

CBS News Aviation Safety analyst Robert Sumwalt told CBS News senior transportation and national correspondent Kris Van Cleave via email that, "Any uncommanded flight control movement is potentially significant. The fact that this resulted in significant damage makes this sort of a big deal." 

The FAA said other airlines haven't reported similar issues and Southwest said it hasn't had a similar issue with other Max jets in its fleet.

Van Cleave notes that the plane involved was delivered in November 2022 and so has been in use for a little over a year. 

The incident was first reported by The Aviation Herald, which said a temporary repair was performed in Oakland and then the aircraft was "ferried" to Boeing's plant in Everett, Wash. for further repairs.

The latest incident comes as the 737 Max remains under heavy scrutiny in the wake of a door plug blowing out of a brand new Alaska Airlines 737 Max 9, which led to a temporary grounding of that Max version.  

In:
• NTSB
• Southwest Airlines
• FAA