The NTSB investigation over the past 17 months found that four bolts securing what is known as the door plug panel were removed and never replaced during a repair as the Boeing 737 Max 9 aircraft was being assembled.
The blowout occurred minutes after the flight took off from Portland, Oregon, and created a roaring air vacuum. Seven passengers and one flight attendant sustained minor injuries, but none of the 177 aboard were killed. Pilots landed the plane safely back at the airport