Airlines are inspecting the controversial aircraft after a midair blowout forced an Alaska jet to make an emergency landing.
The Federal Aviation Administration (FAA), which regulates the industry in the United States, grounded 171 Max 9 planes worldwide after a cabin panel blew off an Alaska-operated plane in midair on Friday, forcing the pilots to make an emergency landing.
United said on Monday that it “found bolts that needed additional tightening,” in its initial inspections.
Alaska said early reports from its technicians indicated some “loose hardware” was visible on some aircraft when it conducted checks of its fleet.
The carriers are focusing on an area known as the door plug, a cover panel used to fill an unneeded emergency exit in aircraft that have been configured with fewer seats.
The panel that blew out on Friday’s Alaskan flight was a door plug and the FAA ordered operators to ground all aircraft with the same configuration.
With 79 Max 9 planes, United has the largest fleet of the aircraft in question. Alaska has 65 of the planes, while the remainder are operated by Turkish Airlines, Panama’s Copa Airlines and Aeromexico.
The midair incident has raised concerns about the production process and quality control for the Max 9. The model is used by relatively few airlines but the 737 Max family of aircraft has been dogged by controversy since the entire global fleet was grounded in March 2019 after two crashes in the space of six months killed 346 people.
Boeing said it was staying in close contact with Max 9 operators and would help customers address any findings during the latest inspections.
“We are committed to ensuring every Boeing airplane meets design specifications and the highest safety and quality standards,” the US plane maker said. “We regret the impact this has had on our customers and their passengers.”
On Monday, the FAA announced that it approved a roadmap for carriers to complete inspections that include both left and right door plugs, components and fasteners. It said planes would remain grounded until operators complete the “enhanced inspections”.
US investigators are continuing to investigate Friday’s incident.
None of the 174 passengers or six crew on the plane suffered serious injuries in the incident even as oxygen masks were deployed and personal items were sucked out of the plane in the sudden depressurisation.
The panel was recovered on Sunday by a Portland teacher who found it in his backyard, National Transportation Safety Board Chair Jennifer Homendy said.