Created Thursday, Mar 7th 2024 20:44Z, last updated Tuesday, Oct 1st 2024 23:00Z
A United Boeing 737-8 MAX, registration N47280 performing flight
UA-1539 from Nassau (Bahamas) to Newark,NJ (USA) with 155 passengers and 6 crew, landed on Newark's runway 04R when during roll out the rudder pedals were stuck in the neutral position. The captain maintained directional control via the steering tiller, rolled out without further incident and taxied the aircraft to the apron.
The aircraft underwent a test flight the following day during which the anomaly was replicated.
On Mar 7th 2024 the NTSB reported:
In a post-incident statement, the captain reported that during the landing rollout, the rudder pedals did not move in response to the “normal” application of foot pressure while attempting to maintain the runway centerline. The pedals remained “stuck” in their neutral position. The captain used the nosewheel steering tiller to keep the airplane near the runway centerline while slowing to a safe taxi speed before exiting the runway onto a high-speed turn-off. While on the high-speed turnoff, the captain asked the first officer to check his rudder pedals and he reported the same problem. The captain reported, that shortly thereafter, the rudder pedals began to operate normally. After parking the aircraft, the flight crew notified UAL maintenance of the flight control malfunction. The airplane was removed from service for maintenance and troubleshooting.
A review of preliminary flight data recorder (FDR) data corroborated the pilot’s statements regarding the malfunction of the rudder system. Data showed that during the landing and subsequent rollout, the rudder surface position remained near its neutral position even though the force inputs to the rudder pedals were observed to be increasing. About 30 seconds after touchdown, a significant pedal force input was observed along with corresponding rudder surface movement. Afterward, the rudder pedals and rudder surface began moving as commanded and continued to function normally for the remainder of the taxi.
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.
The NTSB further reported:
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.
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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.
On Sep 27th 2024 the NTSB issued urgent safety recommendations stating that more than 353 rudder actuators would be affected and stated:
Investigators found evidence of moisture in both actuators, which failed testing. Collins Aerospace subsequently determined that a sealed bearing was incorrectly assembled during production of the actuators, leaving the unsealed side more susceptible to moisture that can freeze and limit rudder system movement.
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The rudder rollout guidance actuator, which is installed in the tail of some B-737NG and 737MAX airplanes, is designed to control the rudder’s movement during category IIIB approach, landing and rollout operations. Although it is not used in non-precision landings, the actuator remains mechanically engaged with the rudder system.
Boeing’s 737 flight manual instructs pilots confronted with a jammed or restricted rudder to “overpower the jammed or restricted system [using] maximum force, including a combined effort of both pilots.” The NTSB expressed concern that this amount of force applied during landing or rollout could result in a large input to the rudder pedals and a sudden, large, and undesired rudder deflection that could unintentionally cause loss of control or departure from a runway.
The NTSB has recommended that Boeing “determine appropriate flight crew responses besides applying maximum pedal force” for such situations in flight or during landing. The NTSB also recommended that Boeing notify flight crews operating 737s with affected actuators that the rudder control system can jam due to moisture that has accumulated inside the actuators and frozen.
Additionally, the NTSB recommended that the FAA determine if actuators with incorrectly assembled bearings should be removed from airplanes, and if so, to direct U.S. operators to do so until replacements are available.
On Sep 30th 2024 the NTSB followed up with a letter to the FAA expressing their concerns that the FAA had not taken action after the first findings and is not appearing to take urgent action now that the NTSB have issued urgent safety recommendations arguing that the aircraft were at risk of loss of control. Two more events with operators outside the USA were known, according to information of the NTSB up to 353 such actuators were produced and delivered, 271 have been installed on aircraft, 16 of them on US Aircraft. The NTSB stated:
Equally concerning is Boeing’s failure to inform United Airlines that the 737 airplanes it had delivered to the airline were equipped with these actuators—and that the actuators were mechanically connected to the rudder control system. We are concerned of the possibility that other airlines are unaware of the presence of these actuators on their 737 airplanes. Consequently, their flight crews may not know what to expect if the rollout guidance actuator fails at low altitude or during landing and rollout, as occurred in this incident. Not making operators fully aware of the installed systems and equipment on the airplanes delivered to them is unacceptable and cannot continue to be tolerated.
Related Flight:
UA1539,
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