The Federal Aviation Administration announced Thursday that it has formally notified Boeing of an investigation into the company’s manufacturing processes after a door plug blew off a Boeing 737 Max 9 jetliner midflight last week.

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“This incident should have never happened and it cannot happen again,” the FAA said in a statement. The agency will investigate “if Boeing failed to ensure completed products conformed to its approved design and were in a condition for safe operation in compliance with FAA regulations.”

In a statement obtained by Reuters, Boeing said it will “cooperate fully and transparently with the FAA and the NTSB on their investigations.”

The investigation stemmed from last week’s incident on Alaska Airlines Flight 1282, when a door plug blew off the side of a Boeing 787 Max 9 jetliner shortly after it took off from Portland International Airport in Oregon. At the time, the plane was carrying 171 passengers and six crew members, according to Alaska.

The plane was forced to make an emergency landing back at the airport with a gaping hole in its fuselage. No serious injuries were reported.

The door plug and two cellphones blown from the plane were later found in the Portland area, according to the National Transportation Safety Board.

The FAA grounded Max 9 jets after the incident, including all 65 flown by Alaska and 79 used by United Airlines, The Associated Press reported. Hundreds of flights scheduled for the planes have since been canceled, including all Alaska Airlines’ flights on the jets through Saturday.

On Monday, United said it found loose bolts while inspecting its Max 9 fleet. Alaska has also said it found loose parts, though formal inspections have yet to begin, according to Reuters.

The NTSB is also investigating.

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NTSB investigates after door plug blown off Alaska Airlines Flight 1282 In this National Transportation Safety Board (NTSB) handout, oxygen masks hang from the fuselage as members of the NTSB examine Alaska Airlines Flight 1282, a Boeing 737 Max 9, on Saturday, Jan. 7, 2024 in Portland, Oregon. A door-sized section near the rear of the plane blew off 10 minutes after Alaska Airlines Flight 1282 took off from Portland, Oregon on January 5 on its way to Ontario, California. (Handout/NTSB via Getty Images)

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