The US National Transportation Safety Board (NTSB) is investigating an United Airlines Boeing 737 MAX 8 flight last month that experienced "stuck" rudder pedals during the landing rollout, the agency said on Thursday.

The NTSB said in a preliminary report on the February 6 flight that the plane taxied to the gate at Newark Airport without incident and there were no injuries to the 161 passengers and crew.

It reported that the captain said that during the landing rollout, the rudder pedals did not move in response to "normal" application of foot pressure while attempting to maintain the runway centerline.

Boeing said it worked with United "to diagnose the rudder response issue observed during two 737-8 flights in early February. With coordination with United, the issue was successfully resolved with the replacement of three parts and the airplane returned to service last month."

Boeing said this is only report of this issue in the 737 MAX fleet. The rudder pedal system is identical to the prior generation 737 NG and the planemaker is aware of two similar occurrences in 2019 on NGs that were resolved through component replacements.

United did not immediately respond to requests for comment. The Federal Aviation Administration referred questions to the NTSB.

Boeing has been under scrutiny in recent months after a January 5 mid-air blowout on another plane model, a Boeing 737 MAX 9. Last month, the FAA formally mandated inspections in Boeing 737 MAX airplanes for loose bolts in the rudder control systems after the planemaker recommended them in December.

The NTSB report said the captain said that in the MAX 8 flight last month the pedals remained "stuck" in their neutral position and the captain used the nosewheel steering tiller to keep the airplane near the runway centerline while slowing to a safe speed before exiting the runway onto a high-speed turn-off. (Reuters)