WASHINGTON (Reuters) - The National Transportation Safety Board said Friday it is opening an investigation into a May 25 in-flight oscillation event involving a Boeing 737 MAX operated by Southwest Airlines.

The NTSB said the plane experienced what was described by the crew as a "Dutch roll" at 34,000 feet enroute from Phoenix, Arizona to Oakland, California. The plane safely landed and no one was injured. Southwest said a subsequent inspection showed damage structural components, the NTSB said.

(Reporting by David Shepardson; editing by Diane Craft)