The US Department of Justice has initiated a criminal investigation into Boeing due to a near-disaster on an Alaska Airlines flight where part of the fuselage blew out.

The investigation is focused on Boeing's adherence to a previous settlement agreement following two fatal 737 MAX crashes.

The FAA responded to the incident by grounding 171 MAX 9 jets with a similar configuration to the one involved in the Alaska Airlines incident.

After completing necessary inspections, Alaska Airlines has resumed service with its MAX 9 fleet.

The NTSB discovered that the door panel separation was due to the absence of four crucial bolts and identified the panel's manufacturer as Spirit AeroSystems, once part of Boeing.

Concerns have emerged regarding Boeing's safety management practices and its level of cooperation with safety investigators.