Alaska Airlines is grounding all 65 of its Boeing 737 MAX-9 aircraft after a harrowing in-flight emergency Friday night left a gaping hole in its fuselage, exposing passengers to the open air.

The big picture: The incident, which didn't end in injuries or fatalities, led the Federal Aviation Administration to require operators of about 171 airplanes worldwide to ground their planes until they were inspected.

• The requirement was issued as part of an Emergency Airworthiness Directive and inspections are expected to take four to eight hours per aircraft, the FAA said in a statement Saturday.

Details: Alaska Airlines Flight 1282 safely returned to Portland International Airport just minutes after takeoff Friday after part of the fuselage flew off for yet-unclear reasons.

• The flight reached a maximum altitude of about 16,000 feet, per aircraft-tracking site FlightAware.
• "There was a really loud bang toward the rear of the plane and a whoosh noise and all of the masks dropped," passenger Evan Smith told local news channel KPTV.

What they're saying: "Each aircraft will be returned to service only after completion of full maintenance and safety inspections," Alaska Airlines CEO Ben Minicucci said in a statement. "We anticipate all inspections will be completed in the next few days."

• Alaska is working with Boeing and the National Transportation Safety Board to figure out what went wrong, Minicucci added.
• Boeing said in a statement Saturday that it supports both the NTSB investigation and the FAA's decision and that Boeing "will remain in close contact" with its regulator and customers.
• "Safety is our top priority and we deeply regret the impact this event has had on our customers and their passengers," the company said.

Be smart: The episode appears to have involved a "plugged" rear exit door.

• "On the 737-9 MAX, Boeing includes a rear cabin exit door aft of the wings, but before the rear exit door," per FlightAware.
• "This is activated in dense seating configurations to meet evacuation requirements. The doors are not activated on Alaska Airlines aircraft and are permanently 'plugged.'"

Of note: It's the latest safety episode for Boeing's 737 MAX family, two members of which crashed in 2018 and 2019 due to problems with a system meant to correct for a nose-up tendency during certain maneuvers.

Between the lines: It's unclear at this point if this is a problem with the entire MAX-9 fleet, or an installation or maintenance issue with this particular aircraft.

Alex's thought bubble: The odds of something like this happening are astronomically low — but it's another good reason (in addition to sudden, unexpected turbulence) to always wear your seat belt on airliners, even when the sign is off.

Go deeper: Boeing urges airlines to inspect planes for possible loose bolt

Editor's note: This story has been updated with a statement from the FAA and Boeing.