The Federal Aviation Administration (FAA) on Saturday ordered the “temporary grounding” of 171 Boeing 737 Max 9 airplanes after a section of fuselage separated from the side of an Alaska Airlines flight on Friday, leaving a gaping hole in the plane. The agency issued an Emergency Airworthiness Directive to airlines requiring that they inspect the planes, which it said in the grounding announcement “will take around four to eight hours per aircraft.”

The New York Times reported Friday that flight 1282 from Portland International Airport had made an emergency landing back at the same airport just 20 minutes later because of a “pressurization issue” that resulted in a wall of the plane blowing out. According to the Times, no one was in the seat immediately next to the wall when it disappeared, and only minor injuries were reported. The abrupt depressurization also reportedly yanked the shirt off of a teenage passenger sitting nearby.

Prior to the FAA’s decision, Alaska Airlines grounded its own fleet of 65 Boeing 737 Max 9 planes for inspection. The company said on Saturday it had inspected over a quarter of its fleet, with “no concerning findings.”

The FAA said on Monday that the EAD it issued requires operators of Boeing 737 Max 9 planes to inspect their planes and fix any issues they find before they can return to service, pending FAA approval. According to the EAD, the FAA has determined that the fuselage plug issue is “likely to exist or develop in other products of the same type design.”

Boeing 737 Max planes have been grounded in the past by the FAA and airlines for other issues, such as problems with the planes’ autopilot that led to two high-profile crashes, and unrelated electrical issues that were later identified. In a 2020 Senate report, the FAA was accused of helping Boeing manipulate recertification tests to get the planes back in service. Most recently, on December 28th, the FAA announced it was monitoring inspections of 737 Max planes after loose bolts were discovered in the rudder-control systems of two planes.

On Friday, The Seattle Times reported that Boeing had petitioned the FAA for a safety exemption for the 737 Max 7, a smaller plane the agency hasn’t certified yet. The plane apparently has a defect that could cause an engine nacelle to break up. The article says existing 737 Max planes with the same defect are allowed to continue operating so long as pilots turn off the plane’s anti-ice system after “icing conditions dissipate to avoid overheating,” which could damage the nacelle. Boeing reportedly called nacelle breakup “extremely improbable” in its petition.

Update January 6th, 2024, 3:10PM ET: Added detail from a Seattle Times article about Boeing’s recent petition for a safety exemption.

Update January 8th, 2024, 1:30PM ET: Added details from the FAA’s Emergency Airworthiness Directive and statement.