The National Transportation Safety Board issued urgent safety recommendations to Boeing over a steering defect related to its 737 planes, adding its growing list of woes.

The National Transportation Safety Board is issuing “urgent safety recommendations” for some Boeing 737s—including the embattled 737 MAX line— warning that critical flight controls could jam.

The National Transportation Safety Board on Thursday 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.