The US National Transportation Safety Board (NTSB) has released preliminary findings from its investigation into an incident involving a Boeing 737 Max. The report suggests that a door which detached from the aircraft shortly after take-off may not have been correctly secured. The incident occurred on an Alaska Airlines flight in January, minutes after the plane had taken off. The report indicates that four crucial bolts, intended to secure the unused door to the plane’s body, seemed to be missing. This lack of bolts may have allowed the door panel to shift and detach from the aircraft. The panel, which covered an unused emergency exit, blew out, creating a large hole in the fuselage just after departure from Portland International Airport. This resulted in a swift drop in cabin pressure as air escaped and the internal atmosphere equalised with the thinner external air.