Southwest Airlines flight from Phoenix to Oakland experiences 'Dutch roll' event mid-air

OAKLAND, Calif. (KGO) -- Details have surfaced about a Southwest flight from Phoenix to Oakland that experienced a scary issue last month.

It's what aviation experts call a "Dutch roll." That's when the plane rocks from side to side in a severe motion while flying.

It happened less than an hour after the Boeing B-737 MAX 8 took off May 25 at an altitude of 34,000 feet.

The pilots were able to regain control and safely made it to Oakland. The National Transportation Safety Board confirms that none of the 175 passengers or six crew members were injured.

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Modern planes have a system to prevent Dutch rolls. But according to the FAA's report on the incident, the plane had a damaged backup power-control unit that was discovered while Southwest was doing maintenance. The airline notified NTSB about the incident and damage on June 7.

In a statement about the investigation, NTSB said:

The NTSB's Vehicle Recorder Laboratory in Washington has received data downloaded from the airplane's digital flight data recorder. Data from the recorder will aid investigators in determining the length and severity of the event.

The cockpit voice recorder, which is currently limited to two hours of audio, was overwritten and unavailable to investigators."

It says a preliminary report is expected within 30 days of the date of the event.