NTSB investigation on Boeing 737 Max 9 revolves around door plug

The National Transportation Safety Board announced their preliminary findings late Monday night after recovering the door plug that blew out from an Alaska Airlines plane while it was mid-flight last Friday, NTSB aeronautical engineer Clint Crookshanks explained that the door plug was used instead of an emergency exit door on some Boeing 737 Max 9 aircraft used by Alaska Airlines and United Airlines.