A federal investigation is underway into how a Southwest Airlines passenger jet suffered significant damage after experiencing a rare phenomenon known as a Dutch roll at nearly 38,000 feet.

Flight N8825Q, a Boeing 737 Max carrying 175 passengers and six crew, was en route from Phoenix to Oakland on May 25 when its tail began to sway left and right, while the plane’s wings swayed sideways.

The Dutch roll is the name given to this dangerous sideways asymmetric movement, which is said to have been inspired by the movements of ice skaters.

The Federal Aviation Administration said in a statement Thursday Boeing is working with the National Transportation Safety Board to investigate the cause of the error.

Boeing declined to comment.

A Initial report The FAA said the plane “experienced a Dutch roll, regained control, and post-flight inspection revealed damage to the standby PCU,” referring to the power-control unit.

The plane landed safely in Oakland and there were no injuries.

Federal Aviation Regulations condition A dutch roll below the permitted speed “must be positively damped without restraints and must be controllable by normal use of the primary controls without requiring exceptional pilot skill.”

In most cases an aircraft’s yaw dampener must correct for lateral movement.

Boeing has been the subject of several investigations — including by the Department of Justice — after an explosion on board a 737 Max 9 in January. The explosion prompted investigators to open investigations into other Boeing planes, including the 787 Dreamliner, after receiving evidence from whistleblowers.

Company He says It has invested heavily in security practices, including using machine learning algorithms to detect potential faults.