NTSB issues an urgent safety alert for the rudder system on Boeing 737MAX aircraft following an incident involving United Airlines with 155 passengers on board

The National Transportation Safety Board (NTSB) has issued an urgent safety alert for a rudder system on Boeing 737MAX aircraft after the rudder pedals on a four-year-old United Airlines Boeing 737MAX-8 briefly jammed as the pilots attempted to land the jet at Newark Airport in February.

The rudder pedals are positioned close to the pilots' feet and, as the name suggests, are used to control the aircraft's rudder. Pressing the left rudder pedal moves the rudder to the left and pressing the right rudder pedal moves the rudder to the right.

When a plane lands, the rudder pedals are used to keep the plane on the centerline of the runway by controlling the plane's yaw motion.

During United Airlines flight UA1539 from Nassau, Bahamas, on February 6, the captain reported that the rudder pedals “stuck” when he pushed down to control the position of the rudder and that they were forced to stop Use nosewheel tiller to keep the aircraft near the runway centerline.

The captain asked the first officer to test the rudder pedals and he also reported that the pedals were stuck in the neutral position. A short time later the pedals began to work as expected.

The NTSB opened an investigation into the incident that focused on one of the rudder control components, a so-called rollout guidance actuator.

Accident investigators tested the rollout guidance actuator involved in the United Airlines incident along with an identical unit from another aircraft. When tested in cold environments, the NTSB found that the function of both actuators was “significantly impaired.”

When investigators examined the actuators more closely, they discovered that moisture had entered the components, causing the tests to fail. The manufacturer, Collins Aerospace, later discovered that a sealed bearing had been assembled incorrectly, which could have caused moisture to enter the component and then freeze.

The NTSB says 353 actuators with the faulty bearing have been delivered to Boeing since 2017, although U.S.-based airlines have already replaced affected rudder systems. However, it is unknown how many faulty actuators are still in use worldwide.

In addition to recommending that airlines urgently replace the faulty actuators, the NTSB also criticized Boeing for the plane maker's recommended actions to resolve a stuck or restricted rudder.

Boeing currently encourages pilots to use “maximum force” to clear a stuck rudder, but the NTSB is concerned that this recommended approach could result in a “sudden, large and undesirable rudder deflection that could inadvertently result in loss of control or runway departure.” could.” .”

A preliminary report on the United Airlines incident was released in March, but the NTSB says the investigation is ongoing.

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