N47280 737-8 Rudder Jam Event

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On 6 Feb 2024, a United Airlines 737-8, N47280, flight UA1539, landed at Newark after a flight from the Bahamas. On the roll out, both crew members found that the rudder pedals were jammed in the neutral position. The crew used the nose wheel steering tiller for directional control and vacated the runway at a high speed turnoff. 30 seconds after touchdown a significant pedal force input was made and the rudder pedals started to behave normally.

A review of preliminary flight data recorder (FDR) data corroborated the pilot’s statements regarding the malfunction of the rudder system.

On February 9, 2024, UAL conducted a test flight on the event airplane at EWR and was able to duplicate the reported rudder system malfunction identified during the incident. As a result, the test flight profile was discontinued, and the airplane returned to EWR and landed uneventfully.

The NTSB was notified of the flight control issue after the flight test and an incident investigation was started. Qualified parties were invited to participate in the investigation. These included the Federal Aviation Administration (FAA), United Airlines, The Boeing Company and Collins Aerospace.

Post-incident troubleshooting and inspection of the rudder control system found no obvious malfunctions with the system or any of its components whose failure would have resulted in the restricted movement observed during flight 1539 and the test flight. As a precaution, the aft rudder input torque tube and associated upper and lower bearings and the rudder rollout guidance servo were removed for further examination by the NTSB systems group. Following the removal of the rudder system components, UAL conducted a second test flight on the airplane and found the rudder control system operated normally.

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*** Updated 05 Aug 2023 ***

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UAL received the incident airplane from Boeing on February 20, 2023, configured with a rudder SVO-730 rollout guidance servo that was disabled per UAL’s delivery requirements to reconfigure the autoflight system from CAT IIIB to CAT IIIA capability. Although the servo was disabled, it remained mechanically connected to the upper portion of the aft rudder input torque tube by the servo’s output crank arm and pushrod.

Diagram showing the location of the rollout guidance servo

On February 28, 2024, the Systems group met at the Collins Aerospace facility in Cedar Rapids, Iowa to examine and test the SVO-730 rollout guidance servo removed from the incident airplane. The testing was conducted to evaluate the effects that temperature “cold soaking” of the servo might have on the torque required to move the servo’s output crank arm. Testing at room temperature found that the torque to rotate the servo’s output crank arm was within design specifications. The unit was then “cold soaked” for 1 hour and the test was repeated. That testing found that the torque to move the servo’s output crank arm was significantly beyond the specified design limits. Because the servo output crank arm is mechanically connected to the rudder input torque tube, the restricted movement of the servo’s output crank arm would prevent the rudder pedals from moving as observed during flight 1539 and the test flight. Further examination of the SVO-730 rollout guidance servo will be conducted as the investigation continues.

The preliminary report can be viewed here: https://t.co/Vt8667Ks0G