A Boeing passenger jet model, the 737 Max 9, remained grounded in the United States on Sunday as airlines awaited instructions from the plane maker and the Federal Aviation Administration on how to inspect the planes and resume service, two days after a harrowing flight raised concerns about the jet.
No one was seriously injured in the episode on an Alaska Airlines flight on Friday night in which a portion of a 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 an immediate call for safety inspections on Max 9 planes with similar seat configurations.
Boeing and the F.A.A. were working to draft a message to airlines — primarily Alaska and United Airlines — with detailed instructions on how to inspect the planes, according to a person familiar with the process. Those discussions were well underway on Sunday, and the F.A.A. has final approval over the contents of the message, as is typically the case.
In the meantime, Alaska, United and other carriers said they had parked all their Max 9 planes, despite stating on Saturday that some were deemed safe to fly. The federal authorities have focused attention on a mid-cabin door plug, which was part of the plane body that was torn out at an altitude of 16,000 feet on Friday and is used to fill the space where an emergency exit would be placed if the plane were configured with more seats.
The National Transportation Safety Board, which is leading an investigation into the episode, has not identified a cause and is searching for the missing piece of the plane. The board said it would look into a wide range of possible factors including F.A.A. oversight, Boeing’s manufacturing process and installation or maintenance work done on the plane.
“Everything’s in, we go very broad, nothing’s excluded,” Jennifer Homendy, the chairwoman of the board, said at a news conference on Saturday night.
The Federal Aviation Administration said on Saturday that the required inspections would affect 171 Max 9 planes operated by U.S. airlines or in U.S. territory. It said the inspections should take four to eight hours per plane to complete. Airlines abroad, including Turkish Airlines and Copa Airlines in Panama, also parked Max 9 planes.
The F.A.A. order contributed to hundreds of canceled flights over the weekend. By early Sunday evening, Alaska had canceled 163 flights, or 21 percent of those scheduled for the day, according to FlightAware. The airline has 65 Max 9 planes. Travelers took to social media to complain about long hold times on the phone for customer service, and inadequate compensation as they waited at the airport and faced lengthy delays and abrupt cancellations.
United Airlines said that it had canceled about 270 flights on Saturday and Sunday that it had planned to carry out aboard its Max 9 planes. It said it was able to preserve another 145 flights over both days by swapping in other planes.
United has 79 Max 9 planes, more than any other carrier. In a statement on Sunday, the airline said that it had parked all those planes and had started removing door panels and performing preliminary inspections on those jets while it awaited further F.A.A. instructions on what inspections would need to be carried out to get the planes flying again.
“We’re continuing to work with the F.A.A. to clarify the inspection process and requirements for returning all Max 9 aircraft to service,” the airline said in a statement. “We are working with customers to reaccommodate them on other flights and in some cases have been able to avoid cancellations by switching to other aircraft types.”
Greg Feith, an aviation security expert and former N.T.S.B. investigator, said this was the type of incident in which it was not “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.”
In the meantime, those who make, service, operate and regulate the planes will all be in the spotlight.
It is not clear whether Boeing is to blame for what happened to the Alaska Airlines plane, but the episode raises new questions for the manufacturer and puts additional pressure on it. 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 pick 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.
“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 contributed reporting.
