NTSB investigates Southwest Airlines ‘Dutch roll’ incident
The US National Transportation Safety Board (NTSB) has issued a preliminary report into a Southwest Airlines’ 16 May ‘Dutch roll’ incident, while it continues to investigate whether “substantial damage” to the rudder system was caused before or after the event.
When reviewing the logbook before Flight 746 took off, the pilot noted a previously recorded yaw damper discrepancy described as “the yaw damper over-correcting in flight”. However, en route from Arizona to California, the aircraft experienced the aerodynamic phenomenon known as Dutch roll; a simultaneous pitching and yawing movement.
The pilot stated that “the roll was stable, more noticeable in frequency, with only a small amount of yaw”. The first officer characterised the event (which lasted a few seconds) as a “strange movement of the tail of the airplane back and forth, coupled with very slight rudder movement left and right,” with the tail movement “noticeable, but not excessive”. Data flight recorder information, analysed by the NTSB, corroborated the flight crew’s statements.
Having informed air traffic control, the pilots descended to 32,000ft, where they experienced similar oscillations before landing in Oakland without any further problems. Subsequent SWA maintenance analysis revealed damage to the vertical stabiliser trailing ribs above and below the standby rudder control unit, considered to be “substantial damage”.
However, further analysis of the flight recorder data indicated that “the anomalous behaviour of the rudder system began on the first after a scheduled maintenance on May 23, 2024”. However, anomalous behaviour was not observed when the aircraft was subsequently dispatched.
