F.A.A. Orders Airlines to Ground Some Boeing 737 Max 9 Jets After Midair Emergency

The Federal Aviation Administration on Saturday ordered U.S. airlines to stop using some Boeing 737 Max 9 planes until they were inspected, less than a day after one of those planes lost a chunk of its body in midair, terrifying passengers until the plane landed safely.

Alaska and United Airlines on Saturday began canceling dozens of flights after grounding their Max 9 fleets so the planes could undergo the federally mandated inspections.

Alaska Airlines Flight 1282 took off from Portland, Ore., on Friday, bound for Ontario, Calif., but was diverted back to Portland six minutes later, according to FlightAware, a flight tracking website. Those on board the flight described an unnerving experience, with wind blowing through a gaping hole that showed the night sky and the city lights below. The plane landed about 20 minutes after it had taken off, and no one aboard was seriously injured.

A passenger, Vi Nguyen of Portland, said that she woke up to a loud sound during the flight. “I open up my eyes and the first thing I see is the oxygen mask right in front of me,” Ms. Nguyen, 22, said. “And I look to the left and the wall on the side of the plane is gone.”

“The first thing I thought was, ‘I’m going to die,’” she added.

The National Transportation Safety Board sent a team to Portland to begin its investigation into the incident.

While the F.A.A. has yet to publicly discuss what caused the incident, it ordered airlines to inspect what it called a “mid cabin door plug.” Some of the Boeing 737 Max 9s are configured with fewer seats and, therefore, do not need all the exits originally designed for the plane. The unneeded doors are filled with a plug. The Alaska Air plane had two of those unneeded doors, located between the rear of the plane and the wing emergency exits, that were “plugged.”

The F.A.A.’s order affects about 171 planes. The agency said that the required inspections should take four to eight hours per plane to complete.

“Safety will continue to drive our decision-making,” the agency’s administrator, Mike Whitaker, said in a statement. The F.A.A. is working with the N.T.S.B.

Boeing issued a statement shortly after the F.A.A.’s grounding order. “Safety is our top priority and we deeply regret the impact this event has had on our customers and their passengers,” Jessica Kowal, a spokeswoman for Boeing, said in the statement. “We agree with and fully support the F.A.A.’s decision to require immediate inspections of 737-9 airplanes with the same configuration as the affected airplane.”

Alaska Airlines confirmed in a statement on Saturday afternoon that it had started inspecting the door plugs and had cleared 18 of its 65 Max 9s to return to service. The airline said it expected to complete the inspections in the next few days. As of midday on Saturday, the airline had canceled about 100 flights, or 13 percent of those scheduled for the day, according to FlightAware. Dozens more flights were delayed.

United Airlines operates more Max 9s than any other airline, according to Cirium, an aviation data provider. Of United’s 79 Max 9s in service, 33 have already been inspected, the airline said in a statement on Saturday. The airline said the removal of the planes from service was expected to cause about 60 cancellations for the day.

“We are working directly with impacted customers to find them alternative travel options,” the airline said in a statement.

Dave Spero, the president of the Professional Aviation Safety Specialists, a union that represents more than 11,000 federal aviation workers including safety inspectors, said on Saturday that aviation safety experts from his union would be on the ground with the N.T.S.B helping them determine how the plug covering the unneeded door was blown out of the plane.

“From our perspective, there is no acceptable type of situation where this kind of thing should happen, this sort of risk shouldn’t be introduced,” Mr. Spero said. “They need to find out how it happened and make sure it doesn’t happen again.”

The plane was just certified in November, according to the F.A.A. registry of aircraft. It entered commercial service that month and has since logged 145 flights, according to Flightradar24, another flight tracking site.

Keith Tonkin, the managing director of Aviation Projects, an aviation consulting company in Brisbane, Australia, said that an excessive difference in the air pressure inside versus outside the cabin could have caused the piece to break off.

“Passengers were probably able to breathe normally even when the plane was at its highest altitude,” Mr. Tonkin added.

A friend of Ms. Nguyen, Elizabeth Le, 20, said she heard “an extremely loud pop.” When she looked up, she saw a large hole on the wall of the plane about two or three rows away, she said.

Ms. Le said that no one was sitting in the window seat next to the hole in the wall, but that a teenage boy and his mother were sitting in the middle and aisle seats. Flight attendants helped them move to the other side of the plane a few minutes later, she said. The boy appeared to have lost his shirt, and his skin looked red and irritated, she added.

“It was honestly horrifying,” she said. “I almost broke down, but I realized I needed to remain calm.”

There were announcements over the speaker system, but none were audible because the wind whipping through the plane was so loud, she said.

Evan Smith, 72, a lawyer who was returning to his home in Murrieta, Calif., after visiting his daughter and son-in-law who live in Portland, said he heard a loud “bang” and saw some “dusky, smoky stuff” swirling around the cabin.

Mr. Smith said his experience as a military police officer taught him that it was important to keep a cool head in these situations. Plus, he said: “The plane was stable. It wasn’t shaking. It wasn’t making any weird maneuvers. It was just flying steady.”

He added, “I was sure the aircraft was fine and we were going to get down OK.”

Passengers were swarming Alaska Airlines’ phone lines on Saturday to rebook canceled flights and determine whether upcoming flights would be affected by the grounding. Customer service hold times, passengers were saying on social media, exceeded seven hours.

Sara Nelson, the president of the Association of Flight Attendants, a union that represents flight attendants at Alaska, United and other airlines, said in a statement on Saturday that she welcomed the inspections required by the F.A.A.

“This is a critical move to ensure the safety of all crew and passengers, as well as confidence in aviation safety,” she said. “Lives must come first always.”

The Air Line Pilots Association, a union that represents pilots at Alaska, United, and other airlines, echoed that sentiment in a statement on Saturday, saying that it applauded the F.A.A. for ordering the grounding to ensure the safety of crews and the flying public.

Boeing’s Max aircraft have a troubled history. After two crashes of Max 8 jets killed hundreds of people within several months in 2018 and 2019, the Max was grounded around the world.

In 2018, Lion Air Flight 610, a 737 Max 8, crashed into the ocean off the coast of Indonesia, killing all 189 passengers and crew members. Less than five months later in 2019, Ethiopian Airlines Flight 302 crashed shortly after leaving Ethiopia’s capital, Addis Ababa, killing all 157 people on board.

The Max planes were grounded after the second crash. Boeing made changes to the plane, including to the flight control system behind the crashes, and the F.A.A. cleared it to fly again in late 2020. In 2021, the company agreed to a $2.5 billion settlement with the Justice Department, resolving a criminal charge that Boeing conspired to defraud the agency.

In December, Boeing urged airlines to inspect all 737 Max airplanes for a possible loose bolt in the rudder-control system after an international airline discovered a bolt with a missing nut during routine maintenance. Alaska Airlines said at the time that it expected to complete inspections for its fleet in the first half of January.

The Max planes are in wide use. Of the nearly 2.9 million flights scheduled globally in January, 4.3 percent are planned to be carried out using Max 8 planes, while 0.7 percent are slated to use the Max 9.

The Max is the most popular plane in Boeing’s history, accounting for a fifth of all orders placed since 1955, according to company data.

John Yoon, Victoria Kim, Orlando Mayorquin, Rebecca Carballo and Christine Chung contributed reporting.