San Francisco, Feb. 6 (Xinhua) -- The preliminary investigation report released by the U.S. National Transportation Safety Board on Feb. 6 shows that the bolts that play a key role in fixing the door plug were not installed when the Boeing 737 Max 9 passenger plane that had a door plug (built-in emergency door) fell off at the beginning of last month.
According to the report, the fuselage of the accident airliner, which was produced by the American company Inerui Aviation Systems, was sent to the Boeing Company's factory in Renton, Washington, for assembly, when it was found that the fuselage rivets were damaged and needed to be disassembled for repairs. **Evidence shows that the bolts securing the door plug were not reinserted after the repair work was completed.
Boeing's statement said it would quickly verify the findings. The company's chief executive, Dave Calhoun, said in a statement that Boeing would continue to cooperate with the investigation.
On Jan. 5, an Alaska Airlines Boeing 737 MAX 9 crashed shortly after takeoff, and a door plug on the side of the cabin fell off. Investigators examined and found that four bolts that were supposed to hold the door plug in place were missing. At the time of the accident, it was only about two months before the airliner was delivered to Alaska Airlines.