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The Federal Aviation Administration (FAA) is set to mandate a one-time inspection for certain 737 Max airplanes following the discovery of loose bolts in a rudder control system, a situation first reported by an operator in December of the previous year.

This finding led Boeing to conduct an extensive inspection of its 737 Max 8, 737 Max 8-200, and 737 Max 9 planes still in production, during which an “under-torqued nut at the same location” was identified. In a statement, Boeing confirmed that subsequent inspections of over 1,400 737 MAX airplanes did not reveal any additional instances of the condition that prompted the initial inspection.

The FAA’s decision for additional scrutiny comes in light of an incident involving an Alaska Airlines 737 Max 9 flight that experienced an “explosive decompression” when a panel plugging an unused emergency exit door detached mid-flight. This incident has amplified concerns regarding the 737 Max’s safety, prompting the FAA to issue an upcoming airworthiness directive scheduled for publication on Monday. Mark Lindquist, representing passengers of the Alaska Airlines flight, expressed severe criticism of the aircraft’s condition, saying, “A plane was delivered by Boeing to Alaska Airlines without four critical bolts, which means the plane was essentially a time bomb. This door plug could have blown off at any time.”

The National Transportation Safety Board’s (NTSB) preliminary report on the incident corroborated the alarming nature of the findings, confirming that “the four bolts that prevent upward movement of the MED [mid exit door] plug were missing before the MED plug moved upward off the stop pads.”