What caused scary 'Dutch roll' on Phoenix flight? Report reveals possible answer

The National Transportation Safety Board released a preliminary report on Tuesday, July 9, providing new details on an in-flight incident aboard a Southwest Airlines Boeing 737 MAX 8 jet that took off from Phoenix Sky Harbor International Airport.

According to NTSB investigators, the plane that experienced a scary Dutch roll on a May 25 flight from Phoenix to Oakland, California, had been parked outside Louis Armstrong New Orleans International Airport during a severe thunderstorm nine days earlier.

The plane underwent routine maintenance two days before the Phoenix-Oakland flight, and investigators observed that movements of the rudder pedal began to occur when yaw damper, which is intended to reduce rocking and rolling motions of the plane, was activated, the report stated.

After the flight, maintenance crews found "substantial damage" to parts inside the jet's tail.

The investigation is ongoing. Here's what we learned from the NTSB report.

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The Boeing 737 MAX 8 was parked outside during severe weather

The NTSB's report suggests severe weather may have damaged the plane that experienced the Dutch roll, though it doesn't conclusively state when and how the damage took place.

On May 16, nine days before the incident, the 737 MAX 8 was parked in a remote part of the New Orleans airport after completing a flight to the city.

That evening and the next day, a line of severe thunderstorms brought gusty winds up to 84 mph (as fast as a Category 1 hurricane) and more than an inch of rain to metro New Orleans. A tornado watch was in effect.

The 737 MAX 8 underwent routine maintenance before Dutch roll

Maintenance records showed that two days before the incident, the plane underwent routine maintenance at William P. Hobby Airport in Houston.

The backup rudder system was tested and no issues were found, according to the NTSB.

What the pilots noticed during the Boeing 737 MAX 8 flight

On May 25, the day of the flight, the captain who flew the plane noticed a previous yaw damper overcorrection was mentioned in the logbook before taking off.

While in flight, he noticed the rudder pedals were stiff, according to the NTSB.

The captain said the plane experienced "a small amount of Dutch roll" after it reached its cruising altitude and going through turbulence. A Dutch roll is when a plane rocks from side to side while its tail yaws, or "wags," making it difficult for the pilot to maintain control.

Investigators said the captain described the roll as "stable, more noticeable in frequency, with only a slight amount of yaw." Yaw is defined as rotation around the vertical axis of the plane.

The flight crew discussed the incident and said they felt the rudder pedals move during the Dutch roll. Although the flight continued to Oakland without incident, the captain said he continued to feel the pedals move after landing.

"They deduced that the oscillations were not caused by the turbulence, as the rudder pedals should not move with the yaw damper system, but rather by the airplane," the NTSB report stated.

What happened to the MAX 8 involved in the Dutch roll?

After the Boeing 737 MAX 8 landed in Oakland, the plane was grounded at Paine Field in Everett, Washington, where Boeing's assembly plant is located. Southwest's maintenance crews took the plane out of service and conducted troubleshooting and inspection.

The maintenance workers found that parts inside the tail were damaged, including the metal support bracket and the vertical stabilizer ribs above and below where the standby rudder power control unit is. NTSB investigators, who assessed the damaged parts last month at an Odgen, Utah, manufacturing facility, described the damage in its report as "substantial."

Southwest Airlines replaced the components. All work was completed and flight tested with the Federal Aviation Administration and NTSB consulting in the process, Southwest spokesperson Lynn Lunsford told The Arizona Republic.

The incident prompted Southwest to inspect its fleet of 231 Boeing 737 MAX jets. The inspections turned up no damage or other issues, according to the NTSB report.

According to the flight tracking websites FlightAware and Flightradar24, the Boeing 737 MAX 8 involved in the Dutch roll is back in service. It flew to Phoenix from Paine Field on July 3 and took off for its first commercial flight after the incident, from Phoenix to Seattle, at 11:12 a.m. July 4.

Boeing declined to comment for this story.

Michael Salerno is an award-winning journalist who’s covered travel and tourism since 2014. His work as The Arizona Republic’s consumer travel reporter aims to help readers navigate the stresses of traveling and get the best value for their money on their vacations. He can be reached at Michael.Salerno@gannett.com. Follow him on X, formerly Twitter: @salerno_phx.

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