The Federal Aviation Administration said that they will temporarily ground and require "immediate inspections of certain Boeing 737 Max 9 planes" after the door on an Alaska Airlines plane blew out mid-flight on Friday night, forcing an emergency landing in Portland, Oregon. 

In a news conference in Portland Saturday night, NTSB Chair Jennifer Homendy called the event an "accident, not an incident."

Homendy, who would not speculate on a cause, said that the plane was forced to return to Portland International Airport just minutes after takeoff "after a mid-cabin door plug...departed the airplane, resulting in rapid decompression."

She said that no one happened to be seated in the two adjoining seats, 26A and 26B, to the blown-out door.

"We are very, very fortunate here that this didn't end up in something more tragic," Homendy told reporters.

Homendy said there were an undisclosed number of "minor injuries," but no severe injuries. The airline also reported that several passengers suffered injuries that required "medical attention," but all have since been "medically cleared."

"With that said, I imagine this was a pretty terrifying event," she said. "We don't often talk about psychological injury, but I'm sure that occurred here." 

Homendy also disclosed the head rests for seats 26A and 25A were lost during the blowout, as was part of the seatback for 26A.

The blowout on Alaska Airlines Flight No. 1282 forced the plane, carrying 174 passengers and six crew members, to make an emergency landing just minutes into its trip from Portland to Ontario, California. 

"All of a sudden I heard, like, a big bang. I didn't know exactly what was going on," one woman aboard the flight told CBS News. "I look up and the oxygen masks were hanging from the ceiling and then I look to my left and there's this huge chunk, part of the airplane just missing. The wind is just extremely loud, there's wind blowing everywhere."

The door blew off at an altitude of about 16,000 feet, Homendy said, noting that it was fortunate that the plane had yet not reached a cruising altitude of between 30,000 and 35,000 feet.

"Think about what happens when you're in cruise," Homendy said. Everybody's up and walking, folks don't have seatbelts on. They're going to restrooms. The flight attendants are providing service to passengers. We could have ended up with something so much more tragic."

The blown-out door still has not been located by authorities. Based on radar, it is believed to be somewhere in the Cedar Mills suburb in the western Portland metropolitan area, Homendy disclosed, off Barnes Road and Highway 217. Anyone who finds it is asked to contact the NTSB. The FBI is assisting in that search.

"Each aircraft will be returned to service only after completion of full maintenance and safety inspections," the airline said. 

Homendy's news conference came just after the FAA released an "Emergency Airworthiness Directive" Saturday evening requiring safety inspections for 171 Boeing 737 Max 9 aircraft in operation worldwide. Such directives are issued "when an unsafe condition exists that requires immediate action by an owner/operator," according to the agency. 

Safety inspections for each plane will take between four and eight hours. There have been about 218 such planes delivered around the world, the FAA said, but not all such aircraft were in operation at the time the EAD was issued. 

"Safety will continue to drive our decision-making as we assist the NTSB's investigation into Alaska Airlines Flight 1282," FAA Administrator Mike Whitaker said. 

Transportation officials applauded the FAA's quick decision. 

Transportation Secretary Pete Buttigieg said Saturday, "Safety will always be the top priority for our Department and for FAA. Administrator Whitaker has acted to order these aircraft grounded pending the inspections necessary to ensure that they are safe to operate." 

The Flight Attendants Union said, "This is a critical move to ensure the safety of all crew and passengers, as well as confidence in aviation safety. Lives must come first always."

Alaska Airlines disclosed in a news release Saturday that the plane in question had been recently delivered from Boeing on Oct. 31. 

"If this had happened at higher altitude, the odds are it could have been a whole lot worse," CBS News travel editor Peter Greenberg said. "...This still seems like an anomaly, because if its actually a design fault with the entire fleet, you have a very serious problem."  

Alaska Airlines said that the portion of the plane which tore off is known as a "plug door — a specific panel of the fuselage near the rear of the aircraft."

The airline said Friday that it would ground all 65 of its Boeing Max 9 aircraft.  On Saturday morning, the airline said that inspections on more than a quarter of the fleet had been completed with "no concerning findings," and that those planes would be returned to service. 

However, after the airline cleared the 18 aircraft, the FAA then issued its order, and all 18 aircraft were again grounded.    

Alaska Air said that it had canceled 160 flights as of Saturday afternoon, impacting about 23,000 fliers. The airline noted that guests whose flights had been canceled by the groundings could rebook their travel or request a refund. 

"We deeply apologize to our guests whose flights have been impacted," the airline said.

Boeing said in a statement to CBS News that "Safety is our top priority and we deeply regret the impact this event has had on our customers and their passengers. We agree with and fully support the FAA's decision to require immediate inspections of 737-9 airplanes with the same configuration as the affected airplane. In addition, a Boeing technical team is supporting the NTSB's investigation into last night's event. We will remain in close contact with our regulator and customers."

In the U.S., only Alaska Airlines and United Airlines use the Boeing 737 Max 9 aircraft. United has about 80 of the planes, but it's not clear how many were operating at the time of the Alaska Airlines incident. United expects about 60 flight cancelations Saturday due to the grounding.

United said the airline is working directly with impacted customers to find them alternative travel options.

In:
• Travel
• Federal Aviation Administration
• Boeing
• Alaska Airlines
• Boeing 737 Max
• Oregon
• California
• United Airlines

Kerry Breen

Kerry Breen is a reporter and news editor at CBSNews.com. A graduate of New York University's Arthur L. Carter School of Journalism, she previously worked at NBC News' TODAY Digital. She covers current events, breaking news and issues including substance use.

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