United finds loose bolts on its planes in wake of Alaska Airlines door plug incident

United Airlines said Monday that it has found loose bolts during inspections of its 737 Max 9 fleet in the wake of a door plug getting blown out of an Alaska Airlines plane over the weekend.

United won't say how many planes had loose bolts.

"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," United said in a statement. "These findings will be remedied by our Tech Ops team to safely return the aircraft to service."

United, like all airlines, had been ordered to take their 737 Max 9s out of service at the order of the Federal Aviation Administration following the door plug falling out of the Alaska Airlines flight Friday.

This is a developing story. Please check back for updates.