NTSB Issues Safety Alert on Boeing 737 Rudder System

DALLAS — The National Transportation Safety Board (NTSB) today issued urgent safety recommendations to Boeing and the Federal Aviation Administration (FAA) in response to "the potential for a jammed or restricted rudder control system on some 737 airplanes."

The safety recommendations stem from an incident involving a United Airlines (UA) Boeing 737-8 whose rudder pedals were "stuck" in neutral during the landing rollout at Newark Liberty International Airport (EWR), Newark, New Jersey, on February 6, 2024.

According to the NTSB, "the captain used the nosewheel steering tiller to control the airplane’s direction after touching down." The 155 passengers and 6 staff members were unharmed, and the plane escaped unscathed. On March 12, the NTSB released a preliminary report outlining the event's details.

One of the incident airplane's rudder control components, a rollout guidance actuator, was examined by NTSB investigators at Collins Aerospace, the component's manufacturer. The incident actuator and an identical one from another airplane were tested in a cold environment, and their operation was considerably affected.

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."

Collins "notified Boeing that more than 353 actuators that Collins had delivered to Boeing since February 2017 were affected by this condition."

United confirmed to theaircurrent.com that it had removed suspect components from nine affected 737 MAX planes earlier this year. These planes, originally built for other operators as white tails, according to John Ostrower, had parts from Collins Aerospace, which had assembly issues with sealed bearings.

One commenter on X thread questioned if Boeing was going to be blamed when the faulty part was produced by Collins Aerospace, noting that the issue was an incorrectly assembled sealed bearing. He also asked if Boeing was responsible for inspecting the part before installation. Another commentator speculated that UA kept this information concealed until now.

Regardless of the numerous questions and inevitable rumors, the overarching sentiment emphasizes concerns about transparency and responsibility among the companies involved.

It is important to note that Rockwell Collins electric servos, which can be part of modern rudder control systems, are widely used in the industry and have been relied on for many decades in all types of aircraft, not just the Boeing 737 MAX, according to avherald.com. It is a dependable component with a great safety record, so it seems odd that it jammed the rudder pedals, which begs the question of how UA is configuring its planes.

Function of the Rollout Guidance Actuator

The rudder rollout guidance actuator, located in the tail of some B-737NG and 737MAX aircraft, is intended to regulate rudder movement during category IIIB approach, landing, and rollout operations. Although it is not used in non-precision landings, the actuator remains mechanically connected to the rudder system.

According to Boeing's 737 flight manual, when presented with a jammed or restricted rudder, pilots should "overpower the jammed or restricted system [using] maximum force, including a combined effort of both pilots."

The NTSB expressed concern that the amount of force delivered during landing or rollout could result in a substantial input to the rudder pedals and a quick, large, and undesirable rudder deflection, potentially causing 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 suggested that Boeing notify flight crews operating 737s with affected actuators that the rudder control system may become jammed owing to moisture accumulating inside the actuators and freezing.

Furthermore, the NTSB suggested that the FAA examine whether actuators with poorly built bearings should be removed from aircraft and, if so, direct U.S. operators to do so until replacements are available.

On November 27, 2018, United Technologies Corporation (UTC) acquired Rockwell Collins Inc., which is now part of Collins Aerospace, a subsidiary of RTX Corporation (previously Raytheon Technologies).

UTC's acquisition of Rockwell Collins is among the largest in aerospace history.Collins Aerospace Systems, an industry leader with 70,000 workers in 300 locations worldwide, boasts US$23 billion in annual sales (pro forma for 2017).

The NTSB Aviation Investigation Report AIR-24-06​ is available online.