The National Transportation Safety Board said it had found a defective part in the system that helps steer the aircraft after investigating an incident at Newark airport.
The National Transportation Safety Board on Thursday issued a safety alert and recommendations for some Boeing planes, warning that a defect could cause the rudder control system that helps steer the aircraft to jam.
The warning applies to some of the company’s 737 Max and 737NG jets. It stems from the agency’s investigation into a United Airlines Boeing 737 Max 8 that experienced “stuck” rudder pedals while landing at Newark Liberty International Airport in February.
The safety board said it had been notified that more than 350 of the defective parts were delivered to Boeing, but it was not immediately clear how many planes with the affected component might be in service. The Federal Aviation Administration said it believed United was the only U.S. operator that had the faulty parts, and United said it had removed the components from its nine affected planes.
The safety board urged the F.A.A. to determine whether the faulty parts should be removed from service and, if so, to mandate that U.S. operators replace them. It also recommended informing international aviation regulators to encourage similar actions. The F.A.A. said in a statement that it had “been monitoring this situation closely” and would convene a panel to determine its next steps.
The warning adds to a string of safety woes for Boeing, which is already under intense scrutiny from regulators after incidents including a panel that blew off a jet midair this year. An audit conducted by the F.A.A. after that incident found dozens of problems throughout the 737 Max’s manufacturing process.
The safety board opened its investigation into the rudder control issue on Feb. 6, after the captain of a 737 Max 8 had to use the nose wheel steering tiller to maintain control of the plane when the rudder pedal became stuck while landing at Newark. A plane’s rudder control is primarily used on takeoff and landing to maintain the direction of the plane’s nose.
After the incident, the board tested a rudder control component known as the rollout guidance actuator from the aircraft and found that the functionality of the part, produced by Collins Aerospace, was “significantly compromised.” The company determined that a sealed bearing was improperly assembled during production, leaving it susceptible to moisture, which can freeze and impede the rudder system’s movements.
“Collins notified Boeing that more than 353 actuators that Collins had delivered to Boeing since February 2017 were affected by this condition,” the safety board said in a statement.
No one was injured in the incident.
Boeing said it was reviewing the safety board’s recommendations and working “to develop additional guidance to address the potential condition.”
“In August, we informed affected 737 operators of a potential condition with the rudder rollout guidance actuator,” the company said in a statement, adding that the component is part of a system that “includes layers of redundancy.”
In its own statement, Collins Aerospace said: “We have and continue to work closely with the N.T.S.B. and Boeing on this investigation. We are supporting Boeing and operators to mitigate operational impacts.”
The Boeing 737 flight manual instructs pilots to apply maximum force if confronted with a jammed or restricted rudder system, according to the safety board. However, the independent safety agency raised concerns that such force during landing could lead to unintended rudder movements, potentially causing the pilot to lose control or the aircraft to veer off the runway.
The safety board recommended that Boeing develop alternative procedures for pilots in such situations and inform crews about the risk of actuator jams because of moisture and freezing.
In its statement, Boeing said it was working to “ensure flight crews have the appropriate operating procedures.”
Niraj Chokshi contributed reporting.
Mark Walker is an investigative reporter focused on transportation. He is based in Washington. More about Mark Walker