Federal investigators said late Monday that it was possible that the bolts that were supposed to keep a fuselage panel in place were never installed before the panel blew off an Alaska Airlines Boeing 737 Max 9 in a near-disastrous accident on Friday night.
That is one of the theories that the National Transportation Safety Board is pursuing as it investigates the blowout, the board’s chairwoman, Jennifer Homendy, said at a news conference in Portland, Ore. Her remarks came hours after United Airlines said it had found loose bolts on similar panels on some of its Max 9 jets while preparing them for inspection after the midair emergency, and Alaska Airlines said it had also found “loose hardware” on Max 9s.
The panel that came off the plane, called a door plug, is placed where an emergency exit door would be if a jet had more seats. Ms. Homendy said on Monday that four bolts, known as stop bolts, should have prevented the door plug from moving upward and coming off the plane.
But the bolts were not on the door plug when investigators recovered it, and they are trying to determine whether they were there to begin with. “We don’t know if they were there or if, again, they came out during the violent explosive decompression event,” Ms. Homendy said.