A school teacher in Oregon has found part of an Alaska Airlines MAX 9 airplane door that blew out mid-flight, the US transport safety authority said on Sunday, in a development that could help with the investigation.
The emergency, which saw no major injuries, prompted airlines and safety bodies around the world to ground some versions of the Boeing 737 MAX 9 jets pending inspections, with dozens of flights cancelled.
The chief of the National Transportation Safety Board (NTSB) said a school teacher found the door panel in his backyard in the city of Portland in the western US state of Oregon.
On Friday, Alaska Flight 1282 departed from Portland International Airport and was still gaining altitude when the cabin crew reported a "pressurization issue", according to the Federal Aviation Administration (FAA), with the plane quickly returning to Portland.
Images posted on social media showed a gaping hole where the side panel had blown out, with emergency oxygen masks hanging from the ceiling.
"I am excited to announce we have found the door plug," NTSB chair Jennifer Homendy said at a press briefing.
A door plug is a cover panel used to fill an unneeded emergency exit in planes with smaller seat configurations.
"He took a picture," she said, referring to the school teacher who she named only as "Bob."
"I can just see the outside of the door plug from the pictures, the white portions. We can't see anything else but we're going to go pick that up and make sure that we begin analysing it."
The FAA said on X that it "is requiring immediate inspections of certain Boeing 737 MAX 9 planes before they can return to flight".
It added that around 171 aircraft worldwide would be affected, with each inspection taking four to eight hours.
US-based Alaska and United Airlines fly the largest number of MAX 9 planes of any carrier and said on Sunday they had grounded their aircraft for inspection.
Other airlines with smaller MAX 9 fleets, including Turkish Airlines, said they did the same.
Boeing has so far delivered about 218 of the 737 MAX planes worldwide, the company told AFP.
The plane manufacturer late Sunday said its chief executive Dave Calhoun has set an all-employee safety meeting for Tuesday at the company's factory in Washington state, and cancelled a leadership summit.
"In light of the Alaska Airlines Flight 1282 in-flight event, we are cancelling the Summit to focus on our support to Alaska Airlines and the ongoing... (NTSB) investigation, and any of our airline customers experiencing impact to their fleets," Calhoun said in a Boeing statement.
Passenger Kyle Rinker told CNN the incident occurred soon after take-off.
"It was really abrupt. Just got to altitude, and the window/wall just popped off," he told the broadcaster.
The NTSB said no one was occupying the two seats nearest the panel, but The Oregonian newspaper quoted passengers as saying a young boy seated in the row had his shirt ripped off by the sudden decompression, injuring him slightly.
According to Aviation Week magazine, airlines that choose MAX models with smaller seating configurations can have the door sealed up, making it look like a typical window from the inside.
The NTSB dispatched a team to Portland to examine the Alaska Airlines craft.
Earlier, Homendy had said it was "very, very fortunate" that the incident had not ended in tragedy.
"We have the safest aviation system in the world. It is incredibly safe," she said. "But we have to maintain that standard."
The plane, which had been heading to Ontario, California, was certified airworthy in October and was newly delivered to Alaska Airlines, according to the FAA registry website.
"Safety is our top priority and we deeply regret the impact this event has had on our customers and their passengers," Boeing said in a statement.
United said 33 of its 46 grounded MAX 9 planes had now been inspected. There were an estimated 60 flight cancellations on Saturday.
Aeromexico said it was grounding all of its 737 MAX 9 planes while inspections were carried out, while Panamanian carrier Copa Airlines said it was grounding 21 of its MAX 9s.
Icelandair said none of its MAX 9's featured the plane configuration specified in the FAA grounding order.
The European Union's Aviation Safety Agency said on Sunday it would follow the FAA's directive, but that it does not believe any EU airlines currently operate the 737 MAX 9.
Boeing has struggled in recent years with technical and quality control issues related to its 737 MAX models.
In December, the US aviation giant told airlines that MAX aircraft should be inspected to check for loose hardware on plane rudder control systems after an international operator discovered a bolt with a missing nut while performing routine maintenance.
Boeing's 737 MAX planes were grounded worldwide following two MAX 8 crashes in 2018 and 2019 that killed 346 people in total.
The FAA approved the planes' return to service only after the company made changes to its flight control system.