A Southwest Airlines Boeing 737 Max experienced damage to its structure after entering a “Dutch roll” during a flight from Phoenix to Oakland, California, on May 25, according to U.S. investigators.
The incident occurred at 34,000 feet, but Southwest did not report the roll or damage to the National Transportation Safety Board (NTSB) until June 7.
After the event, Southwest Airlines conducted maintenance on the aircraft and found damage to structural components, the NTSB stated.
While the NTSB’s comments suggest the seriousness of the incident, aviation experts caution that it is too early to draw definitive conclusions.
A Dutch roll involves a combination of yaw and rocking motion that causes the wings to move up and down. The rhythmic movement is reminiscent of a form of ice skating popular in the Netherlands.
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“It’s just part of aerodynamics,” said John Cox, an aviation-safety consultant and former airline pilot. “What you feel in the back is that the airplane sort of wallows.”
The damage was deemed “substantial.”
Mr. Cox speculated that the structural damage likely occurred in the tail fin of the plane, where the power units are located. He expressed surprise that the backup unit was damaged, as it wouldn’t typically be activated during a Dutch roll.
He noted that Dutch roll two-way oscillation was a concern in older Boeing jets, but design changes in 737s have minimized the risk.
Boeing 737s are designed to naturally dampen Dutch roll without excessive oscillation, Cox explained. In contrast, older models like the 707s and 727s could potentially lead to loss of control due to Dutch roll.
The NTSB retrieved data from the Boeing 737 Max 8 aircraft, aiding in the investigation to determine the severity of the incident.
However, due to the cockpit voice recorder being overwritten after two hours, investigators will not have access to the pilots’ dialogue.
The pilots were able to regain control and safely land the aircraft in Oakland with no reported injuries among the 175 passengers and six crew members.
The NTSB anticipates issuing a preliminary report on the incident within 30 days.
By David Koenig
