Southwest Airlines Boeing jet’s mid-air Dutch roll due to being parked on ground during storm: NTSB Report

A US airline’s Boeing 737 Max 8 jet experienced an unusual “Dutch roll” mid-air after being exposed to a severe storm while parked on the ground, an investigation has found.

The Dutch roll, a swaying, rhythmic combination of yaw and wingtip rocking, occurred on May 25 when a Southwest Airlines flight with 175 passengers onboard was en route from Phoenix to Oakland. The plane started oscillating from side to side at altitudes of 34,000 and 32,000 feet, the Associated Press reported.

The pilots were able to regain control and land the plane safely, with no injuries reported. Pilots are trained to counter Dutch roll, and modern aircraft incorporate yaw dampers to mitigate its effects.

After the incident, the jet was grounded. Mechanics discovered substantial damage to the aircraft’s tail, including fractures in the metal bracket and ribs that hold a backup power control unit to the rudder system.

A preliminary probe report by the National Transportation Safety Board (NTSB) stated that the plane had been parked overnight at the New Orleans airport on May 16 during thunderstorms with gusting winds up to 135 kmph, heavy rain, and a tornado watch.

On May 23, the aircraft underwent scheduled maintenance, and afterward, pilots noticed the rudder pedals moving when the yaw damper was engaged. However, the report does not pinpoint when the damage occurred.

Safety consultant and former airline pilot John Cox told ABC News that the NTSB report indicates that the plane was likely damaged during the storm, with near hurricane-force winds potentially causing the rudder to slam back and forth.

Southwest inspected its 231 Max jets last month and found no other cases of damage around the rudder power units and no problems in new planes received since. The NTSB continues to investigate the incident.

Boeing said it is fully supporting the NTSB’s investigation. Its chief engineer, Howard McKenzie, also clarified that the incident is unrelated to production issues or the 737 Max’s design.