DEEP DIVE: Inside Boeing’s factory lapses that led to the Alaska Air blowout.

The door plug that blew out on Alaska Flight 1282 at 16,000 feet over Portland had sealed a hole cut out of the fuselage for an optional emergency exit door installed by only a few airlines.

Most 737 MAX 9s, like the Alaska jet, have a plug there, not a real door. To a passenger seated at that location, it looks like just another cabin window.

And the mechanics in Renton assembling the airplane don’t typically have to do anything with a door plug. It comes fully installed from Spirit AeroSystems in Wichita, Kan., and there’s usually no reason to open it in Renton.

A specialized door crew in Renton of about 20 to 25 mechanics covering three assembly lines is dedicated to the work of rigging passenger, cargo and other doors. They work first shift, 5 a.m. to 1:30 p.m.

They are the only mechanics that do such work, and even they rarely deal with a door plug. A Boeing manufacturing record lists door plug work performed in Renton just four times last year, one time in 2022 and twice in 2021.

A 35-year veteran on the door team told NTSB investigators that he is “the only one that can work on all the doors” and he was typically the only mechanic who would work on door plugs.

That mechanic was on vacation on the two critical days, Sept. 18 and 19 last year, when the door plug on the Alaska MAX 9 had to be opened and closed.

It’s a lengthy read but worth your time.