Airlines say they found loose parts in door panels during inspections of Boeing Max 9 jets

Federal investigators are learning more about how a door panel flew off an Alaska Airlines jetliner last week

PORTLAND, Ore. -- 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 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.

“Since we began preliminary inspections on Saturday, we have found instances that appear to relate to installation issues in the door plug — for example, bolts that needed additional tightening,” Chicago-based United said.

Alaska said that as it began examining its Max 9s, “Initial reports from our technicians indicate some loose hardware was visible on some aircraft.”

The findings of investigators and the airlines are ratcheting up pressure on Boeing to address concerns that have grown since the terrifying fuselage blowout Friday night. A plug covering a spot left for an emergency door tore off the plane as it flew 16,000 feet (4,800 meters) above Oregon.