Washington DC, United States

A Southwest Airlines-operated Boeing 737 Max was damaged after it went into a “Dutch roll,” said the United States investigators, on Friday (Jun 14).

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What we know about the incident

According to the US National Transportation Safety Board (NTSB), the incident took place last month when the flight at 34,000 feet while en route from Phoenix, Arizona to Oakland, California experienced a “Dutch roll”.  

The Federal Aviation Administration (FAA) has also said that it is working with Boeing and the NTSB to investigate the May 25 incident after it confirmed that the plane experienced the unusual rolling motion. 

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The incident which took place in May was not reported to the NTSB by Southwest Airlines until June 7, said the independent US government investigative agency. 

What is a 'Dutch roll'?

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Dutch rolls occur when a plane oscillates or wobbles on the flight path due to unexpected “asymmetric input” such as wind or pilot commands. It is also a combination of a yawing motion when the tail slides and the plane rocks from wingtip to wingtip. 

The name “Dutch roll” is based on the rhythmic, swaying movement that resembles a form of ice skating that was popular in the Netherlands. The lateral asymmetric movement can also pose serious safety risks.

“It’s just a part of aerodynamics,” said John Cox, a former airline pilot to the Associated Press. He also called the two-way oscillation of a Dutch roll a 'dangerous phenomenon', but not on the 737s. 

The pilots, according to the AP, were later able to regain control and the flight safely landed in Oakland. There were no injuries reported on the flight which was carrying 175 passengers and a crew of six, at the time. 

Flight sustains damage 

A preliminary report by the FAA said that the flight had been inspected after it landed in Oakland and noted that the plane had sustained damage to a unit that provides backup power to the rudder.

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The damage was described as “substantial,” by the federal agency, as per AP.

Meanwhile, the NTSB said it downloaded data from the plane, a Boeing 737, which will help investigators determine the length and severity of the incident.

Both Boeing and Southwest have declined to comment on the Dutch roll incident but confirmed that they are participating in the investigation. 

(With inputs from agencies)