The US Federal Aviation Administration (FAA) has proposed fining Boeing (BOE, Chicago O'Hare) USD5.4 million for allegedly installing nonconforming slat tracks on approximately 178 B737 MAX aircraft.

"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 FAA further alleges that 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.

The proposed fine, which Boeing can challenge within the next 30 days, comes on top of a USD3.9 million penalty proposed by the FAA in December in relation to the same issue affecting 133 B737NG aircraft.

According to the FAA, the affected slat tracks were manufactured by third-tier supplier Southwest United Industries (SUI) and delivered to Spirit AeroSystems. After having learned of the situation itself, Spirit informed Boeing of the situation on or about September 11, 2018, and subsequently proposed that Boeing accept the parts as delivered. Boeing rejected that proposal, leading to Spirit filing a Notice of Escapement in mid-February 2019.

Boeing certified the 178 potentially affected aircraft as airworthy between August 16, 2018, and March 10, 2019.

Boeing said it was aware of the proposed penalty and underlined that the affected slat tracks were covered both by a service bulletin and by an FAA airworthiness directive. The manufacturer added that it did not see any in-service issues related to the parts and stressed that they had no relation to MCAS issues which prompted the grounding of the B737 MAX in mid-March 2019.