The head of the National Transportation Safety Board says the Federal Aviation Administration needs to up the urgency on the potential for jammed flight controls on some Boeing 737s.

The head of the National Transportation Safety Board criticized aviation regulators for “downplaying the urgency” of a possible rudder malfunction on some Boeing 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 followed its urgent safety alert last week about a potential Boeing 737 rudder failure by criticizing the Federal Aviation Administration for a desultory response to the risk and Boeing for not fully informing airlines in advance about the system that failed.

The U.S. National Transportation Safety Board on Monday said more than 40 foreign operators of Boeing (NYSE:BA) 737 planes may have rudder components that could be a safety risk. The warning came after the NTSB last week issued urgent safety recommendations about the possibility of jammed rudder control systems on some 737 airplanes.