The head of the US National Transportation Safety Board criticized US aviation regulators for “downplaying the urgency” of addressing a possible rudder malfunction on some Boeing Co. 737 aircraft in an unusually public rebuke.

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.