Are Boeing 737 Rudder Control Systems at Risk of Malfunctioning?

October 3, 2024

The National Transportation Safety Board on Sept. 26 issued urgent safety recommendations to The Boeing Company and the Federal Aviation Administration in response to the potential for a jammed or restricted rudder control system on some 737 airplanes.

The NTSB is investigating a Feb. 6, 2024, incident in which the rudder pedals on a United Airlines Boeing 737-8, a MAX variant, were “stuck” in their neutral position during the landing rollout at Newark Liberty International Airport, Newark, New Jersey. The captain used the nosewheel steering tiller to control the airplane’s direction after touching down. There was no damage to the airplane or injuries to the 155 passengers and six crewmembers. A preliminary report detailing the circumstances of the event was published on March 12.

NTSB investigators tested one of the rudder control components from the incident airplane, a rollout guidance actuator, at the component’s manufacturer, Collins Aerospace. When the incident actuator and an identical unit from another airplane were tested in a cold environment, the actuators’ function was significantly compromised.

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.

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.

The NTSB also recommended that, if the FAA determines the affected actuators should be removed, notify aviation regulators in other countries that oversee operators of B737 airplanes and encourage them to require removal of the affected actuators until replacements are available.

On Monday, Sept. 30, NTSB Chair Jennifer Homendy sent a letter to FAA Administrator Michael Whitaker expressing concern about the need for the agency to take immediate action on their safety recommendation. The letter also contained more information about the findings of NTSB's ongoing investigation into the 737 rudder control system actuators.

"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," Homendy writes. "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."

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