WASHINGTON, June 14 (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 ( LUV )

.

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 ( LUV ) said a subsequent inspection showed

damage structural components, the NTSB said.