According to a preliminary report by U.S. investigators, which provides the first official version of how the horrific accident happened, the panel holding the door that tore off the Alaska Airlines Boeing 737 MAX 9 plane during a Jan. 5 flight appears to be missing four very important screws . , reports Reuters and CNN, citing News.ro.

Authorities, as well as the public, are anxiously awaiting answers to find out how a panel on a brand new plane came off in flight, an incident that has turned into a true air safety and reputational crisis for a company as large as Boeing.

• VIDEO The Boeing 737 MAX 9 plane lost a part of the fuselage during the flight
• The Alaska Airlines case. The US is grounding 171 Boeing planes for safety checks

Photo evidence released Tuesday shows four screws were missing from the door mounting bracket. According to the NTSB (US National Transportation Safety Board), the lack of wear or deformation around some of the rivets “indicates that the four bolts designed to prevent the prop from moving were missing before it moved.”

Boeing accepted responsibility for the incident in a statement released after the NTSB report and said it was working to prevent similar incidents from happening again. The company has pledged to take new steps to improve the way the 737 Max 9 is made. These include more inspections, giving 737 teams more time to “focus and implement quality improvements” and bringing in outside safety experts to evaluate their operations.

In their 19-page preliminary report released Tuesday, NTSB investigators included observations from a laboratory disassembly of a plane door stopper that fell 16,000 feet at a yard in Oregon. The report stated that the lack of damage to the cover where the screws would have attached it to the fuselage led to the conclusion that the screws were missing during the flight.

The report also includes a photo taken in September, more than a month before the plane was delivered to Alaska Air, showing missing propellers during work on the plane. The photo was taken from a text message exchanged between two Boeing employees and was obtained by NTSB investigators. This means the plane had been flying for several months before the January 5 incident with the missing propellers.

The report was only a preliminary finding and did not assess fault or the cause of the incident. This may appear in the final report, which may take more than a year to publish.

The fact that no one was sitting on the seat near the hole that formed in the side of the plane during the flight is the reason that there were no victims. Six crew members and 171 passengers were on board the plane, which returned safely to Portland International Airport.

It seems that the lack of screws is not the only problem. Both Alaska Airlines and United Airlines said last month that inspections of their fleets after the Jan. 5 incident found loose bolts.

Boeing announced on Sunday that it will have to “fix” improperly punched holes found on the 50 737 Max planes still on the production line that have slowed deliveries.

After the January 5 incident, the US Federal Aviation Administration grounded 171 Boeing 737 MAX 9 aircraft, mainly operated by US airlines United Airlines and Alaska Airlines, for inspection. These aircraft were cleared to return to service at the end of January.

The Federal Aviation Administration (FAA) is conducting a production audit of the 737 MAX, which is looking at all elements of production at Boeing and the production of the airframe at its supplier Spirit.

Boeing shares were up 1.3% on Tuesday afternoon after losing more than 20% of their value since the start of the year.