A BOEING JET NOT SET TO GO

The 'door plug' that blew off an Alaska Airlines plane most likely had manufacturing or installation flaws

- JAMES GLANZ, MIKA GRONDAHL, HELMUTH ROSALES

As Alaska Airlines Flight 1282 made its ascent on January 5, few, if any, passengers knew that a panel called a "door plug" hidden behind the interior surface of the cabin at both window seats in Row 26-was all that stood between them and the cold evening sky. 

Nor did they know that when the jet reached an altitude of 14,830 feet, warning lights began flashing in the cockpit.

Federal investigators say those lights indicated a drop in the cabin's air pressure - perhaps a clue that the panel was failing. At about 16,000 feet, pilots heard a loud boom, and the pressure dropped further: One of those door plugs had completely torn off.

A New York Times analysis of how the door plug is supposed to work, a review of photos and documents, and interviews with aviation experts suggest that manufacturing or installation problems allowed it to come loose and break away just two months after Boeing delivered the 737 Max 9 to Alaska Airlines.

Filling the space that would have been occupied by an emergency exit door if the plane had more seats, the plug relied primarily on two pairs of bolts at the top and bottom, as well as metal pins and pads on the sides to stay in place.

When investigators recovered the plug from a backyard in Portland, Oregon, they found that the door plug itself was largely intact, with the stop pins in place.

The bolts, though, have not been recovered.

Bolts at the bottom of the plug are supposed to prevent it from sliding up vertically, which could lead the stop pins to slip past their contact points, or stop pads, on the plane's body.

Bolts at the top work together with the bottom bolts to prevent the plug from sliding out of the guide rollers and to keep the pins and pads in place. Misalignment of the pins and pads could allow the door plug to open and be blown out, aviation experts said.