The National Transportation Safety Board is in its fourth day investigating how a door plug flew off an Alaska Airlines 737 Max 9 flight taking off from Portland, Oregon. Since the incident, the FAA temporarily grounded all 737 Max 9 planes. Now other airlines are finding loose equipment on their Max planes. “We have not yet recovered the four bolts that restrain it from its vertical movement, and we have not yet determined if they existed there,” said Clint Crooshanks, NTSB Aerospace engineer. This means investigators are trying to figure out if the bolts came off in the blowout. MORE: https://www.cbs8.com/article/news/national/alaska-airlines-737-max-9-commercial-pilot-believes-workmanship-problem/509-f86875b6-c80b-46dc-bf44-0715a6ece73f