The Federal Aviation Administration on Saturday ordered the immediate grounding of some Boeing 737 Max 9 jetliners until they are inspected after an Alaska Airlines plane suffered a blowout that left a gaping hole in the side of the fuselage.

The FAA’s order, which it said will affect about 171 planes worldwide, is the latest blow to Boeing over the Max lineup of jets, which were involved in two deadly crashes shortly after their debut.

The required inspections will take four to eight hours per aircraft.

Alaska Airlines in a statement said that of the 65 737 Max 9 aircraft in its fleet, crews had inspected the paneled-over exits as part of recent maintenance work on 18 planes, and those were cleared to return to service Saturday.

Alaska Airlines Flight 1282 blew out a panel and a portion of its fuselage shortly after takeoff three miles above Oregon late Friday, creating a gaping hole that forced the pilots to make an emergency landing as its 171 passengers and six crew members donned oxygen masks.

No one was seriously hurt as the depressurized plane returned safely to Portland International Airport about 20 minutes after it had departed, but the airline grounded its Boeing 737 Max 9 aircraft until they can be inspected.

The FAA and the National Transportation Safety Board said they would investigate Friday’s incident.

Passenger Evan Smith said a boy and his mother were sitting in the row where the panel blew out and the child’s shirt was sucked off him and out of the plane.

“You heard a big loud bang to the left rear. A whooshing sound and all the oxygen masks deployed instantly and everyone got those on,” Smith told KATU-TV.

Alaska Airlines CEO Ben Minicucci said the inspection of the company’s 737-9 fleet aircraft could take days to complete. They make up a fifth of the company’s 314 planes.

“We are working with Boeing and regulators to understand what occurred ... and will share updates as more information is available,” he said. “My heart goes out to those who were on this flight — I am so sorry for what you experienced.”

On Saturday, Alaska canceled more than 100 flights, or 15% of its schedule, on the West Coast, according to FlightAware.

United Airlines said it had inspected 33 of its 79 Max 9s, and pulling the planes from service had caused about 60 canceled flights.

Photos showed a gaping hole in the Alaska jet where an emergency exit is installed when planes are configured to carry a maximum number of passengers. Alaska plugs those doors because its 737 Max 9 jets don’t have enough seats to trigger the requirement for another emergency exit.

Flight 1282 had taken off from Portland at 5:07 p.m. Friday for a two-hour flight to Ontario, California.

About six minutes later, the window and a chunk of the fuselage blew out as the plane was at about 16,000 feet.

One of the pilots declared an emergency and asked for clearance to descend to 10,000 feet, the altitude where the air would have enough oxygen to breathe safely.

“We need to turn back to Portland,” the pilot told controllers in a calm voice that she maintained throughout the landing process.

The aircraft involved rolled off the assembly line and received its certification two months ago, according to online FAA records.

The plane had been on 145 flights since entering commercial service Nov. 11, said FlightRadar24, another tracking service.

The flight from Portland was the aircraft’s third of the day.

Aviation experts were stunned that a piece would fly off a new aircraft.

Anthony Brickhouse, a professor of aerospace safety at Embry-Riddle Aeronautical University, said he has seen panels of fuselage come off planes before, but couldn’t recall one where passengers “are looking at the lights of the city.”

He also said the incident is a reminder for passengers to stay buckled in.

“If there had been a passenger in that window seat who just happened to have their seat belt off, we’d be looking at a totally different news story,” he said.

Boeing, based in Arlington, Virginia, issued a statement saying it supported the FAA’s decision to require immediate inspections.

The Max is the newest version of Boeing’s venerable 737, a twin-engine, single-aisle plane frequently used on U.S. domestic flights. The plane went into service in May 2017.

The union representing flight attendants at 19 airlines, including Alaska Airlines, commended the crew for keeping passengers safe. “Flight Attendants are trained for emergencies and we work every flight for aviation safety first and foremost,” the Association of Flight Attendants said Saturday.

Two Max 8 jets crashed in 2018 and 2019, killing 346 people and leading to a near two-year worldwide grounding of all Max 8 and Max 9 planes. The planes returned to service only after Boeing made changes to an automated flight control system implicated in the crashes.

Max deliveries have been interrupted at times to fix manufacturing flaws. The company told airlines in December to inspect the planes for a possible loose bolt in the rudder-control system.