NTSB issues 'urgent' safety alert on Boeing 737 radar system as agency investigates Newark Airport issue with United Flight

The National Transportation Safety Board (NTSB) on Thursday issued emergency safety recommendations to Boeing and the Federal Aviation Administration (FAA) in response to possible jammed or restricted radar control systems on some 737 next-generation and 737 Max 8 aircraft.

The rudder controls the side-to-side movement of the aircraft's nose, otherwise known as yaw motion.

The agency is in the middle of an investigation into a February incident in which the radar paddles of a United Airlines Boeing 737 Max 8 were “stuck” in their neutral position while landing at Newark Liberty International Airport in New Jersey.

The captain had to rely on the nose wheel steering tiller, the NTSB said.

The pilots reported that the plane was able to taxi to the gate “without further incident” and disembark the 155 passengers and six crew members. No injuries were reported.

As part of the investigation, NTSB investigators tested one of the rudder control components from the incident aircraft at the component's manufacturer, Collins Aerospace.

After testing in a cold environment, the investigators discovered that the material's performance was “significantly compromised.” Collins Aerospace subsequently discovered that the component had been assembled incorrectly during production.

As part of Boeing's 737 flight manual, pilots who have a jammed or restricted rudder are instructed to “overpower the jammed or restricted system. [using] Maximum power with the combined effort of both pilots.”

However, NTSB investigators expressed concern that this amount of force applied during landing or rollout “could result in a large input to the rudder pedals and cause sudden, large and unwanted rudder deflections that could lead to inadvertent loss of control or departure from the runway.”

Among its recommendations, the agency suggested that aircraft manufacturers determine “the application of maximum pedal force as well as appropriate flight crew response” in such situations in flight or during landing.