Alaska Airlines grounded its Boeing 737 MAX 9 fleet late Friday night after an aircraft departing Portland (PDX) experienced a sudden hull breach and decompression.

The flight, AS 1282, bound for Ontario, California (ONT), safely returned to Portland with 171 passengers and 6 crew members, the airline said.

The flight climbed to as high as 16,300 feet, according to data from FlightRadar24, seven minutes after taking off from Portland, before quickly descending to below 10,000 feet and looping around to return to the airport.

Photos circulating on social media and local news appeared to show a hole the size and shape of an emergency exit “plug” on the left-hand side of the aircraft aft of the wing. The 737 MAX 9 features a spot for an extra emergency exit, which is required on models of the aircraft with certain higher density seating configurations. Airlines that put fewer seats on the aircraft can choose to place a “plug” in that place instead.

NEW IMAGE from on board Alaska Airlines 1282 after ***part of the fuselage*** blew out mid-flight. Successful emergency return to Portland after 20 minutes in the air. 10-week-old (!) Boeing 737 Max 9. NTSB investigating. pic.twitter.com/qjX8fQ1br1

— Pete Muntean (@petemuntean) January 6, 2024

A source familiar with the matter described the moment of decompression as “explosive,” while a passenger on the flight told local media that the force of the incident ripped a child’s shirt off. Photos appeared to show emergency oxygen masks deployed through the passenger cabin.

In a statement, Alaska CEO Ben Minicucci apologized to passengers who were on the flight and said that the airline would ground its 65 737 MAX 9 aircraft pending inspections.

“Each aircraft will be returned to service only after completion of full maintenance and safety inspections. We anticipate all inspections will be completed in the next few days,” Minicucci said. It was unclear Saturday morning whether other airlines operating that aircraft type intended to conduct their own inspections.

Boeing said in a statement that it was assisting in the investigation.