The National Transportation Safety Board chairwoman says heroic actions by the crew aboard an Alaska Airlines flight ensured everyone survived last year when the door plug panel blew out of the plane.

The nation's top safety investigators concluded there were multiple systemic failures that led to a midair blowout during the flight of an Alaska Airlines Boeing 737 Max jet last year.

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.