The Federal Aviation Administration (FAA) plans to impose a US$3.9 million fine on Boeing for allegedly failing to prevent the installation of defective parts on about 130 737 NG airplanes.

Boeing “failed to adequately oversee its suppliers to ensure they complied with the company’s quality assurance system … Boeing knowingly submitted aircraft for final FAA airworthiness certification after determining that the parts could not be used due to a failed strength test,” the FAA said. While Boeing did not admit liability, the company said that  they were aware of the regulatory body’s FAA’s concerns.

“We are working closely with our customers to take the appropriate corrective actions,” spokesman Charles Bickers said in a statement.

According to FAA, Boeing failed to adequately oversee its suppliers to ensure they complied with the company’s quality assurance system. The failure resulted in the installation of slat tracks that were weakened by a condition known as hydrogen embrittlement that occurred during cadmium-titanium plating. Boeing failed to maintain its quality assurance system to ensure suppliers adhered to Federal Aviation Regulations, says the agency.

According to the agency, the affected slat tracks were processed by Southwest United Industries (SUI), a third-tier supplier to Boeing, on June 29, 2018. SUI subsequently shipped the parts to Spirit AeroSystems, Inc. (Spirit), which then delivered the parts to Boeing. The FAA also alleges that SUI notified Kencoa Aerospace, LLC, on July 6, 2018, that a batch of the slat tracks had failed a quality test indicating the presence of hydrogen embrittlement. Kencoa passed that information to Spirit on or about Aug. 3, 2018.

The FAA alleges that Spirit informed Boeing of the situation on or about Sept. 11, 2018, and subsequently proposed that Boeing accept the parts as delivered. On Oct. 9, 2018, Boeing rejected that proposal and instructed Spirit to submit a Notice of Escapement. Spirit filed that notice on Feb. 14, 2019, according to documents.

The FAA further alleges that from Aug. 16, 2018, through Oct. 9, 2018, Boeing certified approximately 48 aircraft potentially equipped with those slat tracks as airworthy. Between Oct. 10, 2018, and May 2, 2019, Boeing knowingly certified an additional 85 potentially affected aircraft as airworthy.

Boeing said that it had not been informed of any in-service issues related to the batch of slat tracks in question. “All affected 737 NGs have been inspected and all slat track installations determined to be required have been completed on the NGs,” the company said.