By CLAIRE RUSH and DAVID KOENIG (Associated Press)

PORTLAND, Ore. (AP) — The Boeing jetliner that suffered an inflight blowout over Oregon was not being used for flights to Hawaii after a warning light that could have indicated a pressurization problem lit up on three different flights, a federal official said Sunday.

Alaska Airlines decided to restrict the aircraft from long flights over water so the plane “could return very quickly to an airport” if the warning light reappeared, National Transportation Safety Board Chair Jennifer Homendy said at a news conference Sunday night.

Homendy cautioned that the pressurization light might be unrelated to Friday’s incident in which a plug covering an unused exit door blew off the Boeing 737 Max 9 as it cruised about 3 miles (4.8 kilometers) over Oregon.

The NTSB said the lost door plug was located Sunday near Portland, Oregon by a school teacher who found it in his backyard, she noted.

Homendy also provided new details about the chaotic scene that unfolded in the aircraft and the cockpit when the plug blew away, leaving a gap in the side of the plane. No one was injured and the plane carrying 171 passengers and six flight crew landed safely back in Portland.

The cockpit door flew open and the depressurization ripped the headset off the co-pilot and the captain lost part of her headset. A quick reference checklist kept within easy reach of the flight crew also flew out the door, Homendy said.

“It was described as chaos and very loud between the air and everything going on around them and it was very violent,” she said.

Hours after the incident, the FAA ordered the grounding of 171 Max 9s, including all those operated by Alaska Airlines and United Airlines, until they could be inspected. The FAA said inspections of each plane will take four to eight hours.

Alaska Airlines and United are the only U.S. airlines that fly the Max 9.

Alaska Airlines and United grounded all of their Boeing 737 Max 9 jetliners again on Sunday while waiting to be told how to inspect the planes to prevent another inflight blowout like the one that damaged the Alaska Airlnes jet.

Alaska Airlines had returned 18 of its 65 737 Max 9 aircraft to service Saturday, but the airline said Sunday that it received a notice from the Federal Aviation Administration that additional work might be needed on those 18 planes.

Alaska said the carrier had canceled 170 flights — more than one-fifth of its schedule — by mid-afternoon on the West Coast because of the groundings and was awaiting further instruction from the FAA. United said it scrapped about 180 flights Sunday while salvaging others by finding other planes not covered by the grounding.

United said it was waiting for Boeing to issue a multi-operator message, which is a service bulletin used when multiple airlines need to perform similar work on a particular type of plane.

Boeing was working on a bulletin, which the company had not yet submitted to the FAA, but producing a detailed, technical bulletin frequently takes a couple days, according to a person familiar with the situation who spoke on condition of anonymity because the company and regulators have not publicly discussed the process.

Boeing declined to comment.

Boeing has delivered 218 Max 9s worldwide, but not all of them are covered by the FAA order. They are among more than 1,300 Max jetliners, mostly the Max 8 variant, sold by the aircraft maker. The Max 8 and other versions of the Boeing 737 are not affected by the grounding.

Democratic U.S. Sen. Maria Cantwell of Washington, chair of the Senate’s Commerce, Science and Transportation Committee, said she agreed with the decision to ground the Max 9s.

“Aviation production has to meet a gold standard, including quality control inspections and strong FAA oversight,” she said in a statement.

NTSB said the chunk of fuselage had been located Sunday by a school teacher named Bob who found it in his backyard and sent the agency two photos. The federal agency had asked for people to be on the lookout for the door plug in an area west of Portland called Cedar Hills.

Earlier Sunday, some local residents were scouring a patch of land with dense thickets, sandwiched between busy roads and a light rail train station. The area is located across from a sprawling hospital complex.

Searcher Adam Pirkle said he had ridden 14 miles (22 kilometers), maneuvering his bicycle through the overgrowth.

“I’ve been looking at the flight track, I was looking at the winds,” he said. “I’ve been trying to focus on wooded areas.”

There has not been a fatal crash involving a U.S. passenger carrier within the country since 2009 when a Colgan Air flight crashed near Buffalo, New York, killing all 49 people on board and one person on the ground. In 2013, an Asiana Airlines flight arriving from South Korea crashed at San Francisco International Airport, killing three of the 307 people on board.

Flight 1282 took off from Portland at 5:07 p.m. Friday for a two-hour flight to Ontario, California. About six minutes later, the chunk of the fuselage blew out as the plane was at about 16,000 feet (4.8 kilometers). One of the pilots declared an emergency and asked for clearance to descend to 10,000 feet (3 kilometers), the altitude where the air would have enough oxygen to breathe safely.

Videos posted by passengers online showed a gaping hole where the paneled-over exit had been and passengers wearing masks. They applauded when the plane landed safely about 13 minutes after the blowout. Firefighters then came down the aisle, asking passengers to remain in their seats as they treated the injured.

It was extremely lucky that the airplane had not yet reached cruising altitude, when passengers and flight attendants might be walking around the cabin, Homendy said.

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

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.

Two Max 8 jets crashed in 2018 and 2019, killing 346 people. All Max 8 and Max 9 planes were grounded worldwide for nearly two years until Boeing made changes to an automated flight control system implicated in the crashes.

The Max has been plagued by other issues, including manufacturing flaws, concern about overheating that led FAA to tell pilots to limit use of an anti-ice system, and a possible loose bolt in the rudder system.

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Koenig reported from Dallas. Associated Press reporter Terry Spencer in Fort Lauderdale, Florida, contributed to this report.