The federal investigation began after a door plug fell off the plane after it took off from Portland International Airport.

After a year and half of investigating, the top U.S. aviation investigator formally determined that Boeing and its chief regulator were to blame for the Alaska Airlines blowout.

The midair blowout in January 2024, which left a gaping hole in the side of the plane operated by Alaska Airlines, didn’t result in any fatalities, but it plunged Boeing into crisis as regulators and policymakers scrutinized quality lapses at the planemaker’s factories.