United Airlines has discovered loose bolts on the door plugs of several Boeing 737 Max 9 planes during inspections. This inspection was initiated after a panel of the same type blew out midflight on Alaska Flight 1282, leading to the grounding of dozens of 737 Max 9s by the Federal Aviation Administration (FAA) on Saturday.

As the largest operator of the 737 Max 9 jet model, United Airlines currently has 79 of these planes in its fleet. The airline began conducting preliminary inspections on Saturday and found instances that indicated installation issues in the door plug, such as bolts requiring additional tightening. United stated that their Tech Ops team is addressing these findings to ensure the safe return of the aircraft to service.

Boeing, the manufacturer of the planes, has issued instructions to airlines to carry out inspections on their 737 Max 9s. United had already begun some preliminary inspection work in recent days.

The incident on Alaska Airlines flight 1282 resulted in no serious injuries; however, the force of the blown-out panel was so strong that it caused some headrests and seatbacks to be ripped from the cabin, and even flung open the cockpit door. The National Transportation Safety Board (NTSB) mentioned that the situation could have been worse if the incident had occurred at cruising altitude when passengers and crew members are moving about the cabin.

This incident has brought renewed attention to Boeing, which has been dealing with quality defects while simultaneously increasing aircraft production, including that of the 737 Max series. Boeing's CEO, Dave Calhoun, has been working to address concerns about the company's supply chain and quality issues. In light of the recent event, Calhoun has canceled a company leadership summit and plans to hold an all-employee call on Tuesday.

Alaska Airlines, with over 60 Boeing 737 Max 9s in its fleet, has not yet commented on whether they have also discovered loose bolts during their inspections. The FAA and Boeing have not provided comments regarding United Airlines' findings.

The Boeing 737 Max is the company's best-selling aircraft, with over 4,000 orders. However, it's worth noting that the grounding primarily affects the Max 8 variant, which constitutes the majority of those orders.

According to aviation publication The Air Current, United Airlines was the first to report the issue of loose bolts on the door plugs.