The US Federal Aviation Administration (FAA) has proposed a $5.4m fine against Boeing for installing faulty slat tracks on around 178 737 MAX aircraft.

Slat tracks are panels installed on the aircraft’s wings to provide additional lift during take-off and landing.

According to the FAA, Boeing failed to ensure its suppliers comply with the federal aviation regulations and the company’s quality assurance system.

Boeing also submitted the aircraft for final FAA airworthiness certification even after the components failed the strength test.

The slat tracks were weakened due to hydrogen embrittlement during cadmium-titanium plating.

Between 29 June and 1 July 2018, Boeing’s third-tier supplier Southwest United Industries (SUI) delivered the affected parts to the manufacturer through Spirit AeroSystems.

On 6 July 2018, SUI informed tier 1 aerostructure supplier Kencoa Aerospace about the failed quality test of the slat tracks.

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After receiving the information on 3 August 2018, Spirit notified Boeing to accept the delivery of the parts.

However, Boeing directed Spirit to file a Notice of Escapement that was done on 14 February last year.

According to FAA’s allegation, Boeing certified 178 affected aircraft as airworthy.

In a statement, the US regulator said: “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 aircraft manufacturer has now one month to respond to FAA’s enforcement letter.

Last month, the FAA proposed a penalty of more than $3.9m against Boeing for installing the same nonconforming components across 133 Boeing 737 NG aircraft.