US investigators focus on Max 9's bolts as airlines find loose parts

[Collection]Federal investigators say a door panel slid up before flying off an Alaska Airlines jetliner last week, and they are looking at whether four bolts that were supposed to help hold the panel in place might have been missing when the plane took off. The comments on Monday from the National Transportation Safety Board came shortly after Alaska and United Airlines reported separately that they found loose parts in the panels - or door plugs - of some other Boeing 737 Max 9 jets.