Investigators are examining a Southwest Airlines jet that experienced a dangerous “Dutch roll” in flight, leading to substantial damage in the tail section where the rudder is located. The Boeing 737 Max was grounded for more than a month after the incident, but has since resumed flights. The plane was parked outside during a severe storm before routine maintenance was performed, during which pilots noticed unusual movements of the rudder pedals. Experts suggest the storm may have caused the damage to the rudder system, rather than the Dutch roll during flight. Southwest has inspected its fleet for similar issues and found no other cases of damage. The National Transportation Safety Board is still investigating the incident and it could be a year or more before a probable cause is determined.