The U.S. National Transportation Safety Board (NTSB) on Monday said more than 40 foreign operators of Boeing 737 airplanes could be using aircraft with rudder components that may pose safety risks.

The NTSB last week issued urgent safety recommendations about the potential for a jammed rudder control system on some Boeing 737 airplanes after a February incident involving a United Airlines flight.

The NTSB also disclosed on Monday that it has learned two foreign operators suffered similar incidents in 2019 involving rollout guidance actuators.