Boeing 737 Max 9 was scheduled for same-day security check the day a cork door came loose from the cabin in mid-flight. Engineers had alerted the company to the unusual lighting of a light warning of a pressurization problem the days before the incident.
The NTSB report revealed that "four bolts intended to prevent the cap holder from moving upwards were missing before it moved" An electronic fault could have been the cause of this failure according to the NTSB. The incident has focused attention on Boeing's manufacturing process.