The “Dutch roll” incident on a Southwest Airlines Boeing 737 Max resulted in “significant” damage to the emergency power control unit.

• A Boeing 737 Max suffered structural damage after the plane entered a Dutch roll during a Southwest flight last month.
• The incident, which occurred at an altitude of 10,330 meters, may be related to a damaged control unit for the emergency power supply, US investigators said.
• Both the agency and the NTSB are investigating the May 25 incident on Flight 746, which was en route from Phoenix to Oakland.
• This movement involves wagging the tail and rocking from side to side. It is named after the movement of a Dutch skating technique.

MAX is in the news again for a rare aerodynamic phenomenon, this time as U.S. aviation safety officials investigate a Southwest Airlines flight that experienced an unusual roll, possibly related to a damaged emergency power unit. The pilots regained control of the “Dutch roll” and landed in Oakland.

The flight operated by Boeing B737 Max 8 landed safely and there were no injuries among the 181 people on the flight between Phoenix and Oakland,California, according to the Federal Aviation Administration.

The incident occurred on May 25 when the plane was flying at an altitude of 34,000 feet, but Southwest notified the National Transportation Safety Board (NTSB) The NTSB said it had no information about the rollover or damage to the plane as of June 7.

A post-flight inspection revealed damage to an emergency power generator and “structural components,” safety authorities said.

“The aircraft suffered “significant” damage to the tail section as a result of the maneuver, but was able to complete the flight. The damage was only discovered during a post-flight inspection. The rudder standby power control unit (PCU) was damaged.”

“Following the incident, SWA performed maintenance on the aircraft and identified damage to structural components.”

The NTSB’s comment may indicate that the incident was more serious than previously known, but aviation experts say it is too early to say for sure.

A Dutch roll is a combination of yaw, i.e. the sideways sliding of the tail, and rocking of the aircraft, in which the wings roll up and down. The name comes from the fact that the rhythmic, swaying movement is reminiscent of a form of ice skating popular in the Netherlands.

“Dutch roll, which is rare in commercial aviation, is an oscillatory motion characterized by a combination of roll and yaw of an aircraft. It typically occurs when the combination of the lateral (roll) and directional (yaw) dynamics of the aircraft are not in balance.”

When a Dutch roll occurs, pilots can often correct it with various control inputs, but most large aircraft have a system that automatically counteracts this, called a yaw damper, so cockpit intervention is often not necessary.

Flight crews train to perform a Dutch roll, and most modern aircraft are equipped with a device called a yaw damper that allows the condition to be corrected by adjusting the rudder.

The NTSB will use information from the plane’s digital flight data recorder to determine the duration and severity of the incident, the agency said in a statement Friday. The cockpit voice recorder is limited to two hours of audio and has been overwritten so it is no longer available.

“The NTSB’s Vehicle Recorder Laboratory in Washington has received data downloaded from the aircraft’s digital flight data recorder. The recorder’s data will help investigators determine the duration and severity of the incident,” the agency said in an emailed statement.

“The cockpit voice recorder, which currently contains only two hours of audio, has been overwritten and is not available to investigators. A preliminary report is expected within 30 days of the incident.”

Southwest said it is cooperating with both agencies in the investigation and the NTSB expects to issue a preliminary report within 30 days.

The NTSB said it expects to release a preliminary report on the incident in about 30 days.

In another recent incident, a Southwest Airlines Boeing 737 Max 8 crashed off the coast of Kaua’i near Lihu’e Airport in April from an altitude of about 1,000 feet at the terrifyingly abnormal speed of over 4,000 feet per minute. It came within 400 feet of crashing into the ocean and it took only seconds to pull the plane back up and climb quickly to avoid the near-disaster.

Show photo credit: YK (X)

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