A harrowing flight over the weekend is again forcing Boeing to confront concerns over its planes, particularly the 737 Max, already one of the most scrutinized jets in history.
No one was seriously injured in the episode on an Alaska Airlines flight Friday night in which a portion of a 737 Max 9 fuselage blew out in midair, exposing passengers to howling wind. The plane landed safely, but the event, on a flight from Portland, Ore., to Ontario, Calif., has spooked travelers and prompted immediate safety inspections on similar planes.
Federal authorities focused attention on a mid-cabin door plug, which is used to fill the space where an emergency exit would be placed if the plane were configured with more seats.
The Federal Aviation Administration ordered the inspection of 171 Max 9 planes operated by Alaska and other U.S. airlines, causing dozens of flight cancellations on Saturday. It said the inspections should take four to eight hours per plane to complete.
“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,” Jessica Kowal, a Boeing spokeswoman, said Saturday.
It is not clear whether Boeing is to blame for what happened, but the episode raises new questions for the manufacturer. Another version of the Max, a 737 Max 8, was involved in two crashes that killed hundreds of people in 2018 and 2019 and led to a worldwide grounding of that plane.
“The issue is what’s going on at Boeing,” said John Goglia, a longtime aviation safety consultant and a retired member of the National Transportation Safety Board, which investigates airplane crashes.
Last month, the company urged airlines to inspect the more than 1,300 delivered Max planes for a possible loose bolt in the rudder-control system. Over the summer, Boeing said a key supplier had improperly drilled holes in a component that helps to maintain cabin pressure. Since then, Boeing has invested in and worked more closely with that supplier, Spirit AeroSystems, to address production problems.
“We are seeing increased stability and quality performance within our own factories, but we’re working to get the supply chain caught up to the same standards,” Boeing’s chief executive, Dave Calhoun, said on a call with investor analysts and reporters in October.
Spirit AeroSystems also worked on the fuselage for the 737 Max 9, including manufacturing and installing the door plug that failed on the Alaska Airlines flight.
Deliveries of another Boeing plane, the twin-aisle 787 Dreamliner, were virtually stalled for more than a year, until the summer of 2022, while the aircraft maker worked with the F.A.A. to address various quality concerns, including paper-thin gaps in the plane’s body.
Another flaw discovered last summer slowed deliveries of the plane again. And production of both the 737 and 787 has been slow to speed up amid those and other problems with quality and the supply chain.
The Max was grounded in early 2019 after two crashes killed a total of 346 people in Indonesia and Ethiopia. Over 20 months, Boeing worked with regulators around the world to fix problems with the plane’s flight control software and other components.
By the time passenger flights aboard the Max resumed in late 2020, the crisis had cost the company about $20 billion.
The two midsize variants of the plane, the Max 8 and Max 9, have been flying since then. But the smallest, the Max 7, and the largest, the Max 10, have yet to be approved by regulators.
The Max is the best-selling plane in Boeing’s history. The more than 4,500 outstanding orders for the plane account for more than 76 percent of Boeing’s order book. The plane is also popular among airlines: Of the nearly three million flights scheduled globally this month, about 5 percent are planned to be carried out using a Max, mostly the Max 8, according to Cirium, an aviation data provider.
Alaska Airlines has 65 Max 9 planes, while United Airlines has 79. Both were conducting inspections on Saturday.
On Sunday, Turkish Airlines announced that it would immediately ground the five Max 9 planes in its fleet until further notice.
Investigators with the National Transportation Safety Board have started looking into the case and are expected to examine a wide range of factors. To start, they are expected to review radar and other data to find the blown-out section of the plane. They are also expected to look into what work Boeing or Alaska Airlines carried out on the plane.
“This is the kind of thing where, until you really get into the investigation — you identify all the facts, conditions and circumstances of this particular event — do you determine whether this is just a one-off or a systemic problem,” said Greg Feith, an aviation security expert and former N.T.S.B. investigator.
In the meantime, those who make, service, operate and regulate the planes will all be in the spotlight.
“Every American deserves a full explanation from Boeing and the F.A.A. on what’s gone wrong and on the steps that are being taken to ensure another incident does not occur in the future,” Senator J.D. Vance, Republican of Ohio, said in a post on Saturday on X.
Mark Walker and Safak Timur contributed reporting.