Investigation underway into rare, unsafe “Dutch roll” of a Boeing 737 Max during a flight to Oakland

By Gregory Wallace | CNN

Federal authorities and Boeing are trying to determine why a rare, unsafe rollover of a 737 Max 8 occurred during flight.

The oscillating motion is known as a “Dutch roll” and a characteristic described by the Federal Aviation Administration (FAA) is the shape of a figure eight through the nose of an aircraft.

There were no injuries on board Southwest Airlines Flight 746 on May 25, according to the airline and a preliminary report from the FAA. The report said the crew “regained control” and the plane landed safely.

However, the aircraft sustained “significant” damage and the FAA classified the incident as an “accident.” The FAA report said an inspection revealed “damage to the standby PCU” (power control unit), which controls the rudder.

It is unclear whether the damaged unit was the cause of the throw or a consequence of it.

The plane has not flown since landing in Oakland, California, following the incident, except to take it to a Boeing facility in Washington state. Boeing did not immediately comment to CNN.