The US National Transportation Safety Board (NTSB) is releasing urgent safety recommendations for certain Boeing 737 aircraft, which includes the troubled 737 Max series, cautioning about the possibility of critical flight controls getting stuck.

The independent investigative agency is issuing the warning that an actuator attached to the rudder on some 737 NG and 737 Max planes could fail.

This caution follows an investigation by the NTSB into a February incident where the pilots of a United Airlines Max 8 plane landing at Newark airport in New York reported that their rudder pedals were stuck in a neutral position.

The US Federal Aviation Administration has stated that it is closely monitoring the situation and will schedule a corrective action review board meeting following the NTSB’s interim suggestions to determine the next course of action on Friday. Boeing has been contacted by CNN for a statement regarding this matter.

The FAA says United Airlines is the only American airline with 737s that use the components in question and that they are no longer being used.

In the last five years, Boeing has suffered a myriad of problems, some tragic and many embarrassing. Most of them have proven financially devastating.

Two fatal crashes of its 737 Max, one in October 2018 and the other in March 2019, killed 346 people and led to a 20-month grounding of Boeing’s best-selling plane and a halt in deliveries to fix a design flaw tied to the crashes.

Boeing then faced a series of other questions about the quality and safety of its planes. That scrutiny grew after a door plug blew off a 737 Max operated by Alaska Airlines shortly after take-off on January 5.

Although no one was killed or seriously injured, the incident sparked numerous federal investigations, one of which revealed the plane had left a Boeing factory without the four bolts needed to hold the door plug in place.

Since then, Boeing has agreed to plead guilty to federal criminal charges of deceiving the Federal Aviation Administration during the initial investigation of the Max.

As part of its agreement with the US Justice Department, the company will have to operate under the supervision of a court-appointed monitor.