The U.S. Federal Aviation Administration has proposed a civil penalty of more than $3.9 million against Boeign for installing nonconforming components on approximately 133 aircraft, which Boeing subsequently presented as ready for airworthiness certification, the agency said in a statement.

“The FAA alleges that Boeing failed to adequately oversee its suppliers to ensure they complied with the company’s quality assurance system. The agency contends that this failure resulted in the installation of slat tracks that were weakened by a condition known as hydrogen embrittlement that occurred during cadmium-titanium plating,” the statement reads.

Boeing has 30 days to respond to the proposal.

In June FFA said 300 NG and 737 MAX airplanes could contain improperly manufactured parts and said it would require these parts to be quickly replaced.

Operation of 737 MAX was suspended after two crashes.  The air crash Ethiopian Airlines in March claimed lives of 157 people, and another 189 people were killed in a crash of Lion Air in Indonesia.