NTSB Issues Urgent Safety Recommendations on Boeing 737 Rudder System
Overall Incident and Response Summary
1. Incident Overview:
- On February 6, 2024, United Airlines flight UA1539, a Boeing 737-8 MAX (N47280), experienced jammed rudder pedals during landing at Newark Liberty International Airport.
- The crew used the nosewheel steering tiller for directional control during landing rollout.
- The rudder pedals returned to normal function after significant force was applied about 30 seconds after touchdown.
2. Investigation Process:
- United Airlines conducted a test flight on February 9, 2024, replicating the issue.
- The NTSB was notified and began an investigation, involving the FAA, United Airlines, Boeing, and Collins Aerospace.
- Flight Data Recorder (FDR) data confirmed the malfunction.
3. Technical Findings:
- The problem was traced to the rollout guidance actuator (servo), manufactured by Collins Aerospace.
- Testing at Collins Aerospace facility on February 28, 2024, revealed that when "cold soaked," the SVO-730 rollout guidance servo's output crank arm required torque significantly beyond design limits.
- Moisture entering the part due to incorrect assembly could freeze at high altitudes, compromising function.
4. Broader Implications:
- Collins Aerospace notified Boeing that up to 353 actuators delivered since February 2017 could be affected.
- This issue potentially impacts both 737 MAX and older 737NG aircraft.
- As many as 40 airlines outside the United States could have aircraft with these parts fitted.
5. Response and Recommendations:
- The NTSB issued urgent safety recommendations to Boeing and the FAA on September 26, 2024.
- United Airlines removed the problematic components from its fleet.
- Boeing informed affected operators in August 2024, but the NTSB is calling for more comprehensive action.
- The NTSB criticized Boeing's current guidance for pilots to use maximum force to overcome jammed rudders, citing potential safety risks during landing.
6. Aircraft Configuration:
- The affected part (rollout guidance actuator) is related to Category 3B autoland capabilities.
- In this case, it had been deactivated at United's request but remained connected to the rudder system.
7. Ongoing Investigation:
- The investigation is continuing, with further examination of the SVO-730 rollout guidance servo planned.
- Final reports and definitive responses from Boeing and the FAA are still pending.
This summary integrates the key points from all provided sources, offering a comprehensive overview of the incident, its investigation, technical findings, and broader implications for aviation safety.
MenTour Video Summary
1. The NTSB issued an urgent safety recommendation regarding potential rudder control system problems on some Boeing 737NG and 737MAX airplanes.
2. The issue stems from a February 6, 2024 incident where a United Airlines Boeing 737-8 MAX experienced stuck rudder pedals during landing at Newark Liberty International Airport.
3. The problem was traced to a part called the rollout guidance actuator, manufactured by Collins Aerospace. Moisture could enter the part due to incorrect assembly, potentially freezing at high altitudes and compromising function.
4. The faulty part was originally intended for Category 3B autoland capabilities but had been deactivated at United's request. However, it remained connected to the rudder system.
5. Collins Aerospace notified Boeing that up to 353 actuators delivered since 2017 could be affected, potentially impacting both 737 MAX and older 737NG aircraft.
6. The NTSB criticized Boeing's current guidance for pilots to use maximum force to overcome jammed rudders, as this could lead to loss of control during landing.
7. United Airlines has removed the problematic components from its fleet. Boeing informed affected operators in August, but the NTSB wants more comprehensive action.
8. The issue wasn't widely known until the NTSB's September announcement, but most affected aircraft should have been addressed in the months following the February incident.
9. The investigation is ongoing, with final reports and definitive responses from Boeing and the FAA still pending.
The video emphasizes that while this is a serious issue, it's not as widespread as some media reports might suggest, and steps have been taken to address the problem in most affected aircraft.
Collins Rollout Guidance Actuator
1. Manufacturer: Collins Aerospace is the manufacturer of the problematic part, specifically the rollout guidance actuator (also referred to as a rollout guidance servo with part number SVO-730).
2. Assembly Error: The root cause of the problem was traced back to Collins Aerospace. The transcript states: "Collins Aerospace subsequently reported that a sealed bearing was incorrectly assembled during production of these actuators, leaving the unsealed side more susceptible to moisture that can freeze and limit rudder system movement."
3. Identification of Affected Parts: Collins notified Boeing about the scope of the problem. They reported that as many as 353 rollout guidance actuators delivered to Boeing since February 2017 could be affected by this assembly issue.
4. Testing: When the NTSB investigated the incident, they conducted tests on the faulty actuator at Collins Aerospace's facilities. These tests, performed in cold environments, confirmed that the actuators' function was significantly compromised due to moisture intrusion and freezing.
5. Supplier to Boeing: Collins Aerospace serves as a key supplier to Boeing, providing critical components for the 737 aircraft, including both the NG and MAX variants.
In summary, Collins Aerospace's role in this issue is central - they manufactured the part, made the assembly error that led to the problem, participated in the investigation by facilitating testing, and provided information about the potential scope of affected parts. Their involvement highlights the complex supply chain in aircraft manufacturing and the importance of quality control at every stage of production.
Summary of Safety Alert
This is a significant development regarding the Boeing 737 rudder system. Let me summarize the key points:
1. The NTSB has issued urgent safety recommendations to Boeing and the FAA regarding potential rudder control system issues on some 737NG and 737MAX airplanes.
2. The recommendations stem from an incident on February 6, 2024, where a United Airlines Boeing 737-8 MAX experienced "stuck" rudder pedals during landing at Newark Liberty International Airport.
3. Investigations revealed that moisture in the rollout guidance actuator could freeze in cold conditions, significantly compromising its function.
4. The issue was traced to incorrectly assembled sealed bearings during production at Collins Aerospace, affecting over 353 actuators delivered to Boeing since February 2017.
5. The NTSB expressed concern about Boeing's current instructions for pilots to use maximum force to overcome jammed or restricted rudder systems, as this could potentially lead to loss of control or runway departure.
6. Recommendations include:
- Boeing should determine alternative responses for flight crews beyond applying maximum pedal force.
- Boeing should notify flight crews about the potential for rudder control system jamming due to frozen moisture.
- The FAA should assess whether affected actuators should be removed from airplanes.
- If removal is deemed necessary, the FAA should notify other countries' aviation regulators to encourage similar action.
7. The investigation is ongoing, and updates may be issued as warranted.
This information is crucial for aviation safety, especially for operators and regulators of Boeing 737NG and 737MAX aircraft. It highlights the importance of addressing potential design and manufacturing issues promptly to ensure passenger safety.
N47280 737-8 Rudder Jam Event
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.
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
Cat IIIB Autoland Capability
A Category 3B autoland capability refers to a specific type of automated landing system used in commercial aircraft. Here's a breakdown of what this means:
1. ILS Categories:
- ILS (Instrument Landing System) approaches are categorized into three main types: Category 1 (Cat 1), Category 2 (Cat 2), and Category 3 (Cat 3).
- These categories are based on the level of precision and the weather conditions they can handle.
2. Category 3 Subcategories:
- Category 3 is further divided into subcategories: 3A, 3B, and theoretically 3C.
3. Category 3B Specifics:
- In a Category 3B approach and landing, the autopilot remains connected after touchdown.
- It maintains directional control of the aircraft during the landing roll-out.
- This allows for landings in very low visibility conditions, though some visual reference to the runway or its lights is still required before landing.
4. Comparison to Other Categories:
- In Category 3A, the autopilot disconnects at touchdown, and the pilot must maintain directional control using the rudder pedals.
- Category 3C (theoretical) would allow for zero-visibility landings, but it's not practically implemented due to taxiing and rescue operation challenges.
5. Equipment Requirements:
- To perform Category 3B autolands, aircraft need specific equipment, including the rollout guidance actuator mentioned in the incident.
- Not all 737s are equipped for Category 3B operations, as it depends on airline preferences, airport infrastructure, and operational needs.
6. Certification and Training:
- Pilots, aircraft, and airports all need special certifications to conduct Category 3B operations.
- Airlines often try to maintain fleet consistency in terms of capabilities for training and operational simplicity.
In the context of the incident, the Boeing 737-8 MAX involved was originally built with Category 3B capability, but United Airlines had requested this system to be deactivated. However, the associated hardware (the rollout guidance actuator) remained in place, which led to the issue when it malfunctioned.
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