United Airlines’ Boeing 737 Max 9 inspections turn up loose bolts

United Airlines said Monday that it has found loose bolts on door plugs of several Boeing 737 Max 9 planes during inspections spurred when a panel of that type blew out during an Alaska Airlines flight using that type of aircraft last week.

The Federal Aviation Administration on Saturday grounded dozens of 737 Max 9s after the panel blew out midflight on Alaska Flight 1282, calling for inspections.

United has 79 of the Max 9 planes in its fleet and is the biggest operator of the jet model.

“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.”

Plane manufacturer Boeing said earlier Monday it issued instructions to airlines to conduct the inspections of the Max 9s in their fleets. United had begun some preliminary inspection work in the past few days.

“We are committed to ensuring every Boeing airplane meets design specifications and the highest safety and quality standards,” Boeing said in a statement Monday evening. “We regret the impact this has had on our customers and their passengers.”

No one was seriously injured in the accident aboard the Alaska Airlines flight, though the blown-out panel produced a force so violent that some headrests and seatbacks were ripped from the cabin and the cockpit door was flung open, according to initial details of a federal safety investigation. No passengers were seated in the two seats next to the panel.

The National Transportation Safety Board said the accident would have been worse at cruising altitude when passengers and crews are walking around the cabin.

But the accident places fresh scrutiny on Boeing, which has…