Officials-Unused Door Cover (plug) Blew Out of Alaska Air 737

According to the latest from Federal investigators, the cause of the massive decompression and emergency landing of an Alaska Airlines 737-9 (Max 9) last Friday evening was a cover used to fill in an unused exit. This is a view of the damage caused to the plane when the cover blew out.

 Unused exits are called door plugs

 According to MyNorthwest.com, all airliners, including the 737 Max 9 (737-9) are built with a required number of emergency exits or exit doors, based on the maximum number of passengers the aircraft is rated to carry.

However, not all airliners use the maximum number of seats.  The seats are removable and airlines reconfigure cabins based on the number of passengers they usually carry on different flights. If a 737 is expected, for example, to carry 75 to 100 people on the routes it is flying, they don't have to have the maximum number of exits or doors.

The ones that are not needed are closed up with what are called door plugs. They are a door-shaped piece of fuselage attached flush in the opening and secured in place. They cannot be removed without tools.

In this case, for some reason, the door plug blew out, causing massive decompression.

  NTSB officials are examining the door plug area

The National Transportation Safety Board has sent numerous parts of the airplane to their headquarters for examination to determine what led to the door plug blowing out. The actual 63 lb. plug was found in the backyard of a home south of Portland, in the flight path of Flight 1282 which was headed to Ontario, CA Friday evening. The blowout and violent decompression happened near Row 26 towards the back of the plane, at an altitude of 16,000 feet. No one was sitting in that row.

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The plane was just a few minutes out from Portland and turned around and made a safe emergency landing.

In the meantime, all Alaska Air 737 Max 9 aircraft remain grounded.