What to know about the Alaska Airlines 737 Max 9 jet that suffered a blowout

An emergency landing by an Alaska Airlines jetliner has prompted U.S. federal authorities to ground some Boeing 737 Max aircraft, adding another episode to the troubled history of Boeing’s Max lineup of jets. The National Transportation Safety Board has begun an investigation that is likely to last months and focus on the paneled-over exit door that blew off Friday night. The FAA has grounded Boeing Max 9 operated by U.S. airlines or flown into the country that have those so-called door plugs are installed. While the Max aircraft has been plagued with problems, none of the previous incidents are related to the blowout the caused Friday's emergency landing. Aviation experts say such blowouts are exceedingly rare in air travel.