SAN FRANCISCO, Sept. 26 (Xinhua) -- The U.S. National Transportation Safety Board (NTSB) Thursday issued urgent safety recommendations to Boeing and the Federal Aviation Administration (FAA) regarding the potential for a jammed or restricted rudder control system on some 737 airplanes.
The NTSB is investigating the incident on Feb. 6, 2024, 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 in New Jersey, the agency said.
NTSB investigators tested a rollout guidance actuator, one of the rudder control components from the incident airplane, 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.
Collins Aerospace subsequently determined that a sealed bearing was incorrectly assembled during the 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.
The NTSB 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 and the FAA determine if actuators with incorrectly assembled bearings should be removed from airplanes.
The agency also recommended that, if the FAA determines the affected actuators should be removed, aviation regulators in other countries that oversee operators of B737 airplanes should be notified and encouraged to require the removal of the affected actuators until replacements are available. ■