Southwest Airlines Boeing 737 MAX Experiences Dutch Roll, Sustains Structural Damage

Oakland, CA – On May 25th, 2024, a Southwest Airlines Boeing 737-8 MAX, registration N8825Q, encountered a significant in-flight event while cruising at FL340 during its flight from Phoenix, Arizona, to Oakland, California. The aircraft, operating as flight WN-746 with 175 passengers and 6 crew members on board, experienced a phenomenon known as Dutch Roll, leading to substantial structural damage.

Incident Overview

The aircraft was en route from Phoenix to Oakland when it encountered a Dutch Roll, a coupled oscillation involving the aircraft’s yaw and roll axes. This phenomenon can occur when there is weakened directional stability, often related to issues with the aircraft’s vertical tail and rudder systems. The flight crew managed to regain control of the aircraft, descending to FL320 and continuing the flight to Oakland, where the plane landed safely on runway 30 approximately 55 minutes later.

Damage and Post-Flight Findings

After landing in Oakland, a post-flight inspection revealed that the aircraft had sustained substantial structural damage. Specifically, the inspection identified damage to the vertical stabilizer’s trailing edge ribs above and below the standby rudder power control unit (PCU). The damage was severe enough to be classified as substantial, compromising the structural integrity of the affected components.

FAA and NTSB Involvement

The Federal Aviation Administration (FAA) reported the incident, noting that the aircraft had experienced a Dutch Roll, regained control, and subsequently discovered damage during the post-flight inspection. The FAA classified the occurrence as an accident due to the extent of the damage.

The National Transportation Safety Board (NTSB) opened an investigation into the event, focusing on the in-flight oscillation and the subsequent damage. The NTSB’s preliminary report, released on July 9th, 2024, provided detailed insights into the incident, including the sequence of events and initial findings from the investigation.

Detailed Sequence of Events

According to the NTSB report, the flight crew encountered the Dutch Roll shortly after reaching their cruising altitude of FL340. The captain, who was the pilot flying, and the first officer, who was monitoring, noted a “small amount of Dutch Roll” that was more noticeable in frequency than in amplitude. The autopilot remained engaged throughout the event, but the crew felt slight movements in the rudder pedals, which indicated that the oscillations were not simply a result of turbulence but were related to the aircraft’s rudder system.

The crew communicated with Air Traffic Control (ATC) and descended to FL320, hoping to find smoother air. However, they experienced similar movements again during the cruise at this lower altitude. Despite these issues, the flight continued to Oakland, where it landed without further incident. The captain reported feeling the same rudder pedal stiffness after landing, prompting further inspection by Southwest Airlines maintenance.

Investigation Findings

The NTSB’s investigation revealed that the rudder system exhibited anomalous behavior beginning on the first flight after scheduled maintenance on May 23, 2024. Data showed that rudder pedal movements occurred when the yaw damper was engaged, a behavior that was not present before the maintenance. The investigation is ongoing, with a focus on determining when the structural damage to the rudder system occurred and identifying the root cause of the Dutch Roll.

Conclusion

The Dutch Roll incident involving Southwest Airlines flight WN-746 on May 25th, 2024, underscores the critical importance of maintaining and inspecting flight control systems, particularly after maintenance work. The event resulted in significant damage to the aircraft, highlighting the potential severity of such in-flight oscillations.

As the NTSB continues its investigation, the findings will likely lead to recommendations aimed at preventing similar incidents in the future, ensuring the continued safety of commercial aviation operations.