(CNN) — The Federal Aviation Administration says it is opening an investigation into Boeing’s quality control after the violent in-flight failure of a door plug on a nearly new 737 Max 9.

In a new statement, the FAA says last Friday’s dramatic in-flight blowout on Alaska Airlines 1282 “should have never happened and it cannot happen again.”

The FAA says the investigation will focus on whether Boeing “failed to ensure completed products conformed to its approved design and were in a condition for safe operation in compliance with FAA regulations.”

The move comes after the two airlines that operate the Max 9 in the United States–Alaska Airlines and United Airlines—found either loose hardware or bolts in the assembly of door plugs on their aircraft. United Airlines says its discovery pointed to possible installation issues. The planes remain grounded pending details on FAA-mandated inspections. The FAA is still reviewing guidance on the inspections from Boeing.

On Wednesday, Boeing CEO Dave Calhoun admitted in an interview with CNBC that the door plug failure was a “horrible escape” of its manufacturing and quality control processes.

In a letter to Boeing, the FAA asks the plane maker to supply any information on the root cause and actions taken to prevent it from happening again. The FAA says Boeing now has 10 days to provide “any evidence or statements” to the agency.

The FAA’s investigation is separate from an investigation begun by the National Transportation Safety Board (NTSB), specifically into the incident itself.

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