Investigators say a door plug on Alaska Airlines 1282 came loose from fittings meant to hold it to the plane ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ United Airlines and Alaska Airlines have discovered loose parts on Boeing BA -1.41%decrease; red down pointing triangle 737 MAX 9 jets that they have inspected after a near-catastrophe on a flight Friday, signaling Boeing’s issues go beyond the aircraft that made an emergency landing. The disclosures came shortly before investigators at the National Transportation Safety Board said that dangerous episode on an Alaska Airlines jet occurred because an emergency exit-sized door plug blew out at around 16,000 feet after...